Richard Baskerville
email: baskerville@acm.org

Robert Davison

Mala Kaul
email: mkaul@unr.edu

Louie Wong
email: louiehmwong@gmail.com

Designing Artifacts for Systems of Information

Keywords: information systems, information technology, design

This paper reports an exploratory study of information systems (IS) design professionals that offers insight into the evolution of the systems concept in systems design practice. The analysis distinguishes the current object of this design effort as systems of information (SI). SI differs from IS in that SI seeks to maintain the necessary degree of integrated systematicity while retaining or acquiring the necessary technology. IS, in the past, had an implied capacity to build a complete system from the ground up. SI has an implied constraint that certain technological components must be "taken as given" and the design problem becomes one of maintaining an ideal socio-technical system as the various technologies evolve within and around the system.

Introduction

Information Systems and Technologies should lie at the heart of both the research and the practice that comprise the discipline and profession of information systems. The elaboration of information systems (IS) with information technologies (IT) can perhaps be traced to Orlikowski and Iacono's [START_REF] Orlikowski | Research Commentary: Desperately Seeking "IT" in IT Research -A Call to Theorizing the IT Artifact[END_REF] authoritative and widely cited 'desperate search' for the IT artifact in IS research. Many current researchers now seek to ensure that the IT artifact is so central to their research that the systems in which these artifacts should be embedded are simply omitted. Lee [START_REF] Lee | Retrospect and Prospect: Information Systems Research in the Last and Next 25 Years[END_REF] listed system as one of the key concepts in the field of information systems research that has been taken-for-granted and has fallen into neglect (the others included information, theory, organization, and relevance). The extent of the problem can be readily perceived in contemporary discourse about cloud computing, service science, experiential computing, and the waves of 'apps' that flood our personal devices -for in all of this, there is little explicit regard for systems.

Where are the systems then? Taken for granted as a tacit assumption? Forgotten or abandoned? Shunted aside or obscured by the clouds? Socially deconstructed, recon-structed or transmogrified into something else? Or are they still here, even though ignored in much of our research and discourse and thus invisible to the audience? Further, what are the consequences of the disappearance or invisibility of systems? Does their absence empower us to new creative heights or impoverish our understanding of how the various components of what we used to call IS fit together? By substituting systems with seductively metaphorical terms like 'clouds' or 'solutions' [START_REF] Morgan | Images of Organization[END_REF], have we deliberately reinvented ourselves as purveyors of delusive simplicity even as we remain custodians of the complex [START_REF]Complexities: Social Studies of Knowledge Practices[END_REF]?

In this article, we explore these systems concepts and their entanglement with our current practice of IS research. We challenge the assumption that IS and IT are identical and instead assert that technology, including design science, technology artifacts and materiality, share the center of the field with socio-technical information systems. We first engage in a review and interpretation of the way IS is conceptualized in the literature. This material is organized into four views, which we term: design engineer, design guide, design gardener, and design therapist. These views, and the common role of designer in these views, resulted from a qualitative study where we explore the perceptions of IS practitioners with respect to the way technology artifacts and information systems are designed and developed. System design was not among the original assumptions when this research was formulated. The role of the practitioners as designers of systems and artifacts arose from the data as a central, shared and defining activity that contextualised widespread practitioner thinking about today's systems and artifacts. Through this process, we reveal current views of technology and systems that will help us to reconceptualize both the technology and the systems of information in contemporary practice. Through an extended discussion, we further reflect on the implications of these views for IS practice and consider future research directions that build on our assertion of the primacy of the system in IS.

Conceptualization of Information Technology and Information Systems

Wikipedia defines information technology as "the application of computers and telecommunications equipment to store, retrieve, transmit and manipulate data, often in the context of a business or other enterprise. The term is commonly used as a synonym for computers and computer networks, but it also encompasses other information distribution technologies such as television and telephones". Oxford English Dictionary [25] defines it as the "branch of technology concerned with the dissemination, processing, and storage of information, esp. by means of computers". The concept has a long history, encompassing developments as old as, for example, the telegraph [START_REF] Gleick | The Information: A History, a Theory, a Flood[END_REF]. The systems concept is well established with a broad agreement on its general meaning. An analysis of the definitions for the concept finds that the most common textbook definitions are very similar. A system is an assembly or set of interacting entities or elements with relations between them [START_REF] Backlund | The Definition of System[END_REF]. In a system, the behavior of each element has an effect on the behavior of the whole, and these behaviors are interdependent. Elements can form subsystems, and these subsystems also affect the behavior of the system as a whole. The connectivity is such that independent subsystems cannot form. A system is a whole that cannot be divided into independent parts. Interaction is important: one element's behavior is influenced by another. The relationships between elements in a system are defined by behavior, and such behavior means each element has significant properties that may change. For an element to be considered as being inside a system, it means that the element must affect parts of the system and also must be affected by parts of the system [START_REF] Backlund | The Definition of System[END_REF].

From an IS perspective, the systems concept is anchored in general systems theory [START_REF] Ashby | General Systems Theory as a New Discipline[END_REF][START_REF] Boulding | General Systems Theory -The Skeleton of Science[END_REF] and systems science [START_REF] Ackoff | Science in the Systems Age: Beyond IE, OR, and MS[END_REF][START_REF]Facets of Systems Science[END_REF]. Systems theory was quickly adapted as information systems theory [START_REF] Ackoff | Management Misinformation Systems[END_REF][START_REF] Langesfors | Information Systems Theory[END_REF], especially in its "soft" variety that merged action research and systems science into a form of systems thinking and soft systems methodology [START_REF] Checkland | Systems Thinking, Systems Practice[END_REF]. The application of systems theory as a means of coping with complexity emerged as a central purpose of the concepts [START_REF] Ashby | Requisite Variety and its Implications for the Control of Complex Systems[END_REF][START_REF] Flood | Dealing with Complexity: An Introduction to the Theory and Application of Systems Science[END_REF]. Open, biological, and social systems concepts provide attractive explanations for behavioral changes arising in the social-technical nature of the use of information technologies in the workplace [START_REF] Bertalanffy | The History and Status of General Systems Theory[END_REF]. The notion that communication is the defining operation in a social system offers an essential justifying role for information systems [START_REF] Luhmann | System as Difference[END_REF]. Also thematic is the notion that systems, once created, can have a certain autonomy and durability, meaning they can be self-organizing [START_REF] Ashby | Principles of the Self-Organizing Dynamic System[END_REF][START_REF] Varela | The Principles for Self-Organization[END_REF] and self-reproducing (autopoietic) [START_REF] Luhmann | The Autopoiesis of Social Systems[END_REF][START_REF] Varela | Autopoiesis: The Organization of Living Systems, Its Characterization and a Model[END_REF].

Despite the fairly broad agreement on the defining aspects of a "system", there are rather more diverse definitions of information systems. For example, there are different kinds of things that have been labeled as information systems, such as: organizations that deliver information to their clients; systems of active elements that deal only with symbolic objects (i.e., information); the subsystem within any self-governing system that enables communication between the managerial or operational subsystems of an organization [START_REF] Carvalho | Information System? Which One Do You Mean?[END_REF]. Lee [START_REF] Lee | Retrospect and Prospect: Information Systems Research in the Last and Next 25 Years[END_REF] divided the information system into three interacting and constituent subsystems: the organization system, the data system, and the technology system. A study of more than 20 published definitions of IS confirms this potential disagreement. Most include references to computers or technology, and most refer to organizations; and while some mention society or social aspects, a few entirely ignore IT, organizations and society, taking for example a database perspective. In general, what agreement can be found in the literature suggests that IS are systems in which human participants and/or machines use information, technology, and other resources to produce informational products and/or services [4, p. 451].

One reason for this diversity in the conceptualization of IS may partly lie in the relegation of the systems concept into the background as part of the IS assumption ground. This relegation can be useful when the purpose is to understand the consequences of the IS in its context, i.e., what the IS contributes or creates. As an example, Riemer and Johnston [START_REF] Riemer | Rethinking the Place of the Artefact in IS using Heidegger's Analysis of Equipment[END_REF] explain the IT artifact as a kind of Heideggerian equipment that, while co-constituting practice and social identity, fades from notice as it is absorbed into use. Its role as the embodiment of a system or as a component of a system is lost to the preeminence of its consequences. It is mainly argued as either distinct from other components or hopelessly entangled with other components such that its role may only be to materialize social purpose without necessarily taking notice that a social-technical system exists. We see similar effects from the debates over whether social and material aspects of information systems are separable or inextricably entangled [START_REF] Leonardi | Materiality and Change: Challenges to Building Better Theory about Technology and Organizing[END_REF][START_REF] Orlikowski | Sociomaterial Practices; Exploring Technology at Work[END_REF]. The latter position effectively black-boxes the social technical system as a somewhat impenetrable sociomaterial system in order to add clarity to its socially constructive consequences. For example, Pentland [START_REF] Pentland | Dynamics of Organizational Routines: A Generative Model[END_REF] employs the social materiality concept to help us more clearly observe the ability of a system to retain patterns of action.

The systems aspect of IS is assumed, at best, to be shared and taken-for-granted when in fact there may be some disagreement about just which aspects of the systems concept are more dominantly valued in a particular IS perspective. Based on systems theory, there are two key dimensions along which the systems perspective can vary [START_REF] Ackoff | Creating the Corporate Future: Plan or Be Planned For[END_REF][START_REF]Facets of Systems Science[END_REF]. One dimension aligns with the distinction between the elements of a system versus the relations between, or interactivity of, those system elements [START_REF] Backlund | The Definition of System[END_REF]. A designer might dominantly value the discrete information technologies that make up the system. Such a component-focused designer would approach a system design task as one of integrating available components. We will designate this approach as an integrating components viewpoint. 1 Alternatively, a designer might dominantly value the relationships and interactions between these technologies, the accompanying data and the people who constitute the system. Such a relationship-focused designer would approach a system design task as one of growing or nurturing a healthy or sustainable ecology within (and perhaps in the outside environment of) the system. We will designate this approach as fitting an emergent ecology viewpoint. To an important degree, this dimension represents a contrast between an IT assumption and an IS assumption.

The second dimension considers the behavior of the elements within a system in affecting the behavior of the system. At an organizational level, this dimension aligns with a design distinction between the ways in which the system interacts with the complex aspects of its environment (such as culture). For our purposes, this dimension is helpful in distinguishing between a 'controlling-the-complexity' design culture versus a 'coping-with-complexity' design culture. For the control perspective, a designer might dominantly value the importance of the system in controlling the complexity of its organizational environment. For example, the system designer might aim to prevent diverse cultural settings from affecting system performance. Such a control-focused designer would approach their design task as one designing a system where the system may help manage and control. This view is consistent with Boulding's lower levels of systems complexity and is exemplified by control mechanisms in cybernetic systems, such as a thermostat [START_REF] Boulding | General Systems Theory -The Skeleton of Science[END_REF]. We will designate this extreme approach as a control the complexity viewpoint. Opposite this viewpoint, a designer might dominantly value the importance of the system in matching and interoperating with the complexity of its organizational setting. At this perspective, the designer would view the cultural context of an organization as one that is adaptable to the system, where the system does not deterministically control how work is done. This view is consistent with Boulding's higher levels of systems complexity and is exemplified by societal systems made up of communicating, autonomous human beings [START_REF] Boulding | General Systems Theory -The Skeleton of Science[END_REF]. We will designate this approach as a coping with complexity viewpoint.

Collectively, these two dimensions provide indications of the "how" and "why" of systems designers. The vertical axis suggests why systems designers take various design decisions, and the organizational cultural contexts wherein those design decisions are made. The design decisions may be influenced by a flexible organizational culture and environment where systems must be dynamically adaptable to the infinite variety of circumstances. Alternatively, the design decisions may be driven by a corporate mandate to control the behavior of an organization (and its various component parts, including people). The second dimension helps explain how a system is being designed. For example an emphasis on a solution using discrete components represents an IT-centric design decision. On the other hand, an emphasis on the interrelationships between such components, as well as the data, models, procedures and people who use them represents an IS-centric design decision. These two dimensions help define four divergent design views of designing the systems aspect of information systems, which we discuss next. We consider these four design views first from the Complexity-Controlling aspect. Where there is a mandate to control organizational behavior, an emphasis on discrete technological components implies a system design view we call Design Engineer. An emphasis on the interrelations between these components implies a system design view we call Design Guide.

System Designer as Design Engineer: The system is assumed to be the amalgamation of a set of discrete technologies and people. Their ability to interact is less important than their discrete capabilities. This viewpoint involves the assumption that the setting for the system is an organization that can be built and controlled. Centralization is frequently a core attribute in this control setting, with the system helping organize and control the organizational complexity.

System Designer as Design Guide: The system is assumed to be the interaction of the whole set of interconnected system technologies and people. The individual capability of each system element is less important than its contribution to system activities as a whole. This viewpoint involves the assumption that the setting for the system is an organization that can be built and controlled. In order to achieve this, system designers must guide the organization in order to discover the strong shared-purpose in connecting technologies and people. The system is designed to organize and control the natural complexity of the organizational context, but is done through relationship-building (both within the technical system and the human community).

Where there is a design culture that places less emphasis on controlling organizational behavior and more emphasis on adaptation between system and organization, an emphasis on discrete technological components implies a design view we call Design Gardener. An emphasis on the interrelations between these components implies a view we call Design Therapist.

System Designer as Design Gardener: The system is assumed to be the amalgamation of a set of independent technological artifacts or people. Their ability to interact with each other or with other system components is less important than their discrete capabilities. Like a gardener choosing which plants to grow in which corners of a garden, this viewpoint involves the assumption that the setting for the system is a dynamic organizational environment that will operate more-or-less independently of control mechanisms. Design decisions must provide an avenue to cope with the infinite variety of circumstances in this environment. The goal of the system designer is to choose the right system elements that will best adapt to organizational complexities, rather than to control them.

System Designer as Design Therapist: The system is assumed to involve emergent interactions among interconnected sets of system technologies and people. The individual capability of each system element is less important than its dynamic integration in system activities as a whole. This viewpoint involves the assumption that the setting for the system is a changing ecological environment that operates more-or-less independently of control mechanisms. The goal of the system is to cope with and adapt to the natural complexity of the environment, rather than to control it. Like a therapist who helps a patient change holistically to a better state, this system design viewpoint is characterized by highly organic assumptions about both technical and human systems. The designer helps the system holistically to cope with change through emergence.

Methodology

We developed our theoretical framework using logic and analysis of concepts in the literature. In order to determine if it reflects design viewpoints held in practice, we planned a qualitative field study using interview guidelines. The choice of a qualitative form of such a field study is driven by the exploratory nature of the framework. Because the systems concept is open to interpretation by the respondents, it was important to trap richer qualitative data at this stage of the development of the theoretical framework (i.e. allow researchers to be surprised by the data), rather than incorporate an attempt to nail the study to a single conceptualization of the systems idea [START_REF] Klein | A Set of Principles for Conducting and Evaluating Interpretive Field Studies in Information Systems[END_REF][START_REF] Walsham | Doing Interpretive Research[END_REF]. The field study reflects the selection of firms and practitioners who assume differing roles in designing information systems. It is important to retain qualitative values for this study because a single actor may enact multiple roles. When this occurs, the researchers require the latitude to offer interpretations of the role assumed by a subject in relation to offering a particular reflection for the study, relying on cues that may be in the margins of the qualitative data. While we cannot experimentally manipulate the role assumed by the respondents, we can select respondents that represent differing roles. Because this selection process involves interpretation, the qualitative nature of the study remains continuous [START_REF] Walsham | Doing Interpretive Research[END_REF].

Similarly, the design views must also be captured qualitatively. It requires conceptualizations described by respondents of (1) their system setting and (2) their focus given to either the discreteness of technologies or the integrated nature of systems. In this sense, our respondents are selected on the basis that they constitute natural hosts for four viewpoints about technology and the settings in which technology is situated.

Research Procedure

We examined 12 cases, each representing a practicing IS professional involved in system design in the various roles described. We collected data aiming to assess three cases in at least four different roles (vendor, CIO, consultant, etc.). Three cases provide sufficient confidence that design viewpoints discovered would be present in multiple cases (i.e., more than one). Our objective is not to prove any universality, but only to detect cases of the four expected design viewpoints (design engineer, design guide, design gardener, and design therapist). Three cases in each category provide three opportunities to find the expected effects. Further, in the 12 selected cases, we examined cases in two geographic regions in order to reveal possible cultural differences. For each role, at least one case was examined in Hong Kong and at least one case in the USA.

We used a semi-structured interview guide that (1) collected simple demographic information to provide a sense for possible alternative explanations for the conditions;

(2) offered the subject an opportunity to describe and explain their role in relation to systems and systems design; (3) offered the subject an opportunity to describe and explain their assumptions about the systems setting; and (4) offered the subject an opportunity to describe and explain their assumptions about technology and its relations. In the interview guide, section (2) was explicit about the role enacted by the subject (the expected independent condition), however both (3) and (4) were intentionally less direct, intending to provide an ideal setting for the subject to reveal the presence in their design thinking of their attitude about the two dependent conditions.

Examples from The Findings

The analysis of the interview data provided illustrations of the way our information systems practitioners conceptualize systems along the dimensions described above.

Design Gardener View

Dave, Business Intelligence Manager in a US Manufacturing Firm of some 21,000 employees, provided indications of this view. The system is assumed to involve the amalgamation of a set of discrete technologies or people. Their ability to interact is less important than their discrete capabilities. Dave described a litany of incompatible systems that were pasted together post hoc:

We have the finance system; we have a plant maintenance system …we have time management systems, and…our HR is really outsourced, so I shouldn't count that. We do have billing, ordering, and picking up systems -so that's all in one area. We do have data warehouse. There's a lot of use of access databases … So most of them are, let's say, I want to use the word, artificially put together. What that means is we found solutions to transfer data from one to another if they are not originally directly compatible.

Design Guide View

Horace, a CTO and Chief ERP Architect for a Hong Kong manufacturing firm of some 28,000 employees provided indications of this view. The system is assumed to be the interaction of the whole set of interconnected system technologies and people. Even though, historically, individual technology silos may have existed, the individual capability of each system element is now less important than its contribution as a participant in system activities as a whole. For Horace, this is about the value of ERP systems and how the standardizing systems fit the business need for sharing information:

ERP is centralized. The reason to centralize is we want to share information, not because we want to control. A good example is we do internal transfer of raw materials. If we transfer fabric from one factory to another, the system will handle all the inter-company charges automatically. But if you use two separate systems, you need to build your own interfaces. Another example is we share fabric. So one customer has orders in both plants. And if we need fabric, plant A can check their inventory for plant B. So for technical reasons, we centralize.

Design Therapist View

The system is assumed to be the interaction of the interconnected set of system technologies and people. The individual capability of each system element is less important than its contribution to system activities as a whole. This viewpoint involves the assumption that the setting for the system is a changing ecological environment that will operate more-or-less independently of control mechanisms. The setting is complex, but the goal of the system is to cope with the complexity rather than to control it.

Jerzy, an IT services manager for a small Hong Kong IT services firm of about 10 employees, expressed opinions consistent with this view; particularly noting the tensions between users and the technology. These tensions moderate the way each system component can contribute to the larger system as a whole.

The information system helps us retain memories about previous projects. Ultimately, we want to have the system acting as the company's memory on all existing and historical projects and help recall what we did in the past and facilitate reuse of previous works. This is just like a large search engine for the company.

Although the system can operate quasi-independently, in an SME there needs to be a reasonably tight hold on systems and procedures: However, management and control works are still there. We can't pass that to the information system and people do not 100% trust the system.

Design Engineer View

The system is assumed to be the amalgamation of a set of discrete technologies and people. Their ability to interact is less important than their discrete capabilities. This viewpoint involves the assumption that the setting for the system is an organization that can be built and controlled. The setting is complex, and the system can help organize and control this complexity. Alice, a CIO of a US manufacturing firm of about 30,000 employees, provided an indication of this view. She points out that technologies and people are entities that must be controlled. Systems provide the means for controlling these discrete elements:

Major systems such as ERPs are the life blood of compliance within our organization and are on the critical path to management and control. In our business, the consequence of putting the wrong technology or people into operation can be catastrophic -it can lead to loss of face with customer, missing out on contractual obligations and missing on commitments to shareholders.

Discussion: Systems of Information

The data provided many further indicators of concepts illustrated in the examples above. Our positioning of the statements above should not be taken as instances of positioning each respondent neatly and holistically into one of the quadrants. Indeed, three of the respondents provided bifurcated perspectives. These comments can be interpreted as a respondent whose perspective is in motion, a possible transition from one viewpoint to another. Rather, we argue that the statements likely represent a momentof-reflection that fits the noted position. We are mapping these moments-of-reflection rather than mapping people. While these positions may indeed suggest a general orientation of the person who made the statement, it is quite possible that the mapping would be quite different if the individual reflected on a different situation. We are also investigating the presence of systems concepts among the reflections of information specialists. Such systems-oriented reflections are not the bailiwick of information systems alone. From the outset of the IS field, we have understood that systems concepts broadly inhabit diverse disciplines. For example, when Thomas Haigh asked Charles Bachman about "systems people" in the early days of computing at Hewlett-Packard; Bachman replied, … they were certainly concerned with systems, but they weren't generic systems people. They were functionally specialized. I guess they were all systems people, whatever they had to do. They were concerned with: 'How to manufacture things?' 'How to ship things?' 'How to pay for things?' People were specialists in 'how to do it.' If that makes you, a systems person, so be it. It was not specialized to information systems. It could be whatever, but it was a way to handle professional specialization. [15, p. 42] As a consequence, it is likely that the grid in Table 1 can also be used to map reflections from a complexity-control, complexity-coping, component-integrating, and ecology-emerging perspective across a diverse range of human occupations. Our particular interest however, was observing information specialists reflecting on systems concepts, as opposed to other kinds of specialists.

We sought to discover the ways in which IS management employed the systems concept. We began with the apparent conflation of IT and IS. In this area, we sought to discover the ways in which the systems concept was currently used by information specialists, and whether this could be distinguished from the technology concept.

We found indications that an entanglement between IT and IS was less of an issue than an entanglement of practice and design within current IS management thinking. Surprisingly, the respondents were generally focused on how to organize and execute transitions from current systems to future systems. They were designing future systems, given the constraints and affordances of their current technologies and people.

We distinguish the object of this design effort as systems of information (SI). SI differs from IS in that SI seeks to maintain the necessary degree of integrated systematicity while retaining or acquiring the necessary technology. IS, in the past, had an implied capacity to build a complete system from the ground up. Even if this capacity is not a necessity, SI has an implied constraint that certain technological components must be "taken as given" and the design problem becomes one of maintaining an ideal sociotechnical system as the required technologies evolve in and around the system. The reconceptualization of IS as SI reflects the reversal of field that is taking place in the practice of systems design. It involves the practice of experiential design, a form of design and redesign that is contemporaneously integrated with the lived experience of the object-of-design.

For example, the presence of an ERP (or ERP-like) system at the enterprise level is often taken for granted in the systems reflections of our respondents. Their challenge is to acquire new capabilities (i.e., new technologies) while maintaining systematic qualities such as efficiency, effectiveness, usability, etc. The problem, from the CIO level down, is how to satisfy new demands from internal stakeholders or external clients by acquiring and integrating new technologies without compromising the enterprise's essential socio-technical systematicity. They were thus engaged in the difficult design problem of getting from here to there without wrecking the overall system's benefits. The technological problem can be viewed most vividly as a cutting-edge new component ("a trendy new app"). The systems problem is most typically viewed as one of integration ("how can I add this trendy new app and keep my enterprise up"). This is the design focus of SI, making integrated systems out of commoditized components. SI is oriented to the ideal design of technological mash-ups [START_REF] Gamble | Monoliths to Mashups: Increasing Opportunistic Assets[END_REF].

The SI design problem is no less socio-technical than the IS design problem. IS designers focused on building usable information systems with ideal social and technical characteristics. The SI design problem is different in that it is more similar to architectural programming because of the mash-up constraints. Certain technological features are given and the population of users is given. The SI challenge is to program the entanglement between these people and that technology as well as the entanglement between that technology and the pre-existing system -and data.

As a consequence, the entanglement artifact is different from other kinds of artifacts. The SI designer is designing not only the typical artifacts, such as technologies, models and processes, but also the entanglement (programming the mash-up). This new kind of artifact, the programmed entanglement, presents a more complex systems problem to the designer, who needs to exercise not only considerable care and innovation, but also wisdom and contextual intelligence. The large number of predefined constraints and affordances that arise when programming (or reprogramming) a mash-up in the presence of a new technology or component constitute a significant issue. It appears that this new kind of SI design is being carried out at widely varying levels of the IS function within the organization.

The results of the foregoing study have limitations. As an interpretive and qualitative study it does not respond to typical positivist criteria such as repeatability and reliability. The respondents, their positions and the firms represented in the cases were not random, but were intentionally selected to provide a diversity of viewpoints on the discrete complexity-control, complexity-coping, component-integrating, and ecologyemerging. Our aim was not to study designers per se, choosing instead to focus more on managerial positions. The validity of theoretical generalizability arises in the care in the design of this diversity, not from the limited quantity of respondents. While we were certainly successful in achieving an ideal spread of reflections, the data did not support classifying a respondent entirely in one quadrant or another. Rather, respondents appeared to situate themselves in whichever quadrant was appropriate for the moment at hand. Thus, given an infinite variety of organizational circumstances, each with its own technologies, problems and people, so an equally infinite variety of positions can be proposed in order to ensure optimal organizational functioning. The dynamic flexibility and contextual intelligence that this requires of the SI designer implies that any design space within the systems quadrant may be inhabited at any one time by the same designer, depending on the circumstances. The implication for IS researchers is that they need to be more sensitive to organizational circumstances (people, problems, technology) when they analyze either the behavior of designers or the artifacts that they design. A purely design guide perspective, for instance, cannot hope to meet the exigencies of all conditions. In different circumstances, and in particular as an organization evolves, so perspectives can shift. As Leonard pointed out, as his company has grown from a local to a global logistics provider, so his view of systems has shifted from one of gardening to one of guiding. Other companies may see the reverse, or something different: there is no ideal state that can apply to all companies in all circumstances. However, benchmarking against the competition can be a useful exercise.

Conclusion

Our research indicates that the conceptual conflation of information systems and information technology is misleading. Information specialists reflect differently on their work using these two concepts in distinctive ways. From this perspective, little has changed in the way IS and IT concepts are present in practice. However, we did discover that the way information specialists are conducting design in their work is quite surprising. Rather than designing information systems in holistic ways, information specialists are designing system usage programmatically, being very careful to preserve the systematicity of information practices, while acquiring the necessary current technologies. We term this new aspect of design practice systems of information to distinguish the particular practice of programming the entanglement of new technologies with old technologies and the entanglement of technologies with people. This entanglement is a reversal of field in the practice of systems design. Designers are experiencing their lives within an environment that is defined by previous systems designs while concomitantly experiencing their own designs as new technologies are inserted, appended, or overlapped with old systems. The need to maintain integrated systematicity while retaining or acquiring the necessary technology is central to SI. System design today only rarely evokes a capacity to build an entire new system from the ground up. That form of systems design is the "old" IS. Today, systems design operates on a platform constrained by a set of technological components must be retained in and for the new system. The design problem has become one of maintaining an ideal socio-technical system as the required technologies evolve in and around the system.

Table 1 .

 1 Different system viewpoints

	View toward Interacting with The Environment	Dominant Designer Value Integrating Fitting Emergent Components Ecology
	Control the Complexity	Design Engineer	Design Guide
	Cope with the Complexity	Design Gardener	Design Therapist

While the primary elements of systems used in this paper are consistent with existing systems literature, the labels and terminology used in this paper for the various dimensions and viewpoints of systems emerged from the data analysis described later in the paper.


A Kao
email: a.kao@gre.ac.uk

N Shevchenko

O Roshchupinka

S Eckert

Koulis Pericleous

Thin Sample Alloy Solidification in Electromagnetic Driven Convection

Keywords: Gallium Indium, Thin Sample Solidification, Natural convection, Forced convection, Thermoelectricmagnetohydrodynamics

During the directional solidification of Ga-In25%wt., density variations in the liquid cause plumes of solute to be ejected from the interface through natural convection. This can lead to the formation of chimneys during solidification and ultimately freckles. The application of external magnetic fields can be used to suppress these plumes. Two magnetic systems are considered. The first is a rotating magnetic wheel, which provides conditions analogous to forced convection at the solidification interface. The forced convection causes preferential growth of secondary branches and causes the plumes to be transported downstream and back into the bulk. The second is through the application of a static magnetic field that interacts with inherent thermoelectric currents, generating a Lorentz force that drives fluid flow within the inter-dendritic region. However, in the bulk where there are no thermoelectric currents, electromagnetic damping dominates and plumes are stunted. Using a fully coupled transient numerical model each of these systems has been analysed. Comparisons to experiments are given for the cases of natural and forced convection. The experimental setup uses a Hele-Shaw cell with an electric heater and Peltier cooler, allowing for control over the thermal gradient and cooling rate.

Introduction

Convective transport of solute is known to have a dramatic effect on the evolution of the underlying microstructure of alloys during solidification. In many cases the fluid flow is an inherent part of the process, for example, natural convection is significant in alloys that have relatively large density differences between the various components causing plumes of solute to be ejected back into the melt. These can lead to preferential flow channels (or chimneys) and ultimately the formation of freckles. This phenomenon is common in Nickel based super alloys which are widely used in the manufacturing of gas turbine blades [1][2][3]. Performing direct in situ experimental studies on Nickel based super alloys is very difficult due to the high solidification temperature. An alternative system to study the underlying mechanism is the Gallium-Indium system, which is liquid at room temperature and easy to handle. Furthermore, due to a relatively large density difference between Gallium and Indium, the system exhibits similar flow behaviour to Nickel based super alloys. An in situ radiographic technique for Ga-In systems isused in this work to validate the numerical studies. This technique has previously been used by Eckert and co-workers [4][5][6].

Numerical models have been used to investigate the formation of freckles in castings [7][8][9], however they have primarily focused on the effects of natural convection flow. This work focuses on the introduction of external forces in the liquid to controlthe fluid dynamics. In the first instance the application of a magnetic wheel generates an alternating magnetic field providing conditions analogous to forced convection close to the solidification front. The secondexperimentconcernsthe application of a static external magnetic field, leading to two effects;the first is electromagnetic damping, the second thermoelectric magnetohydrodynamics (TEMHD). The latter is caused by the magnetic flux interaction with thermoelectric currents,localised to the solidification front giving a resultant Lorentz force, hence driving fluid flow. In this work a fully coupled transient 3-dimensional numerical model was applied to each of these cases. The model uses an Enthalpy based method originating from the work ofVoller [10]. This has been substantially extended by Kao et al. [11,12] into a 3-dimensionalmulti-scale method, that includes fluid flow and electromagnetics. The capability to predict the outcome of microstructural modifications due to externally applied forces will allow for macroscopic material properties to be tailored by selective design of these forces.

Governing Equations

Due to the low Reynolds number encountered on the scale of microstructures and thin sample experiments, a simplified form of the incompressibleNavier-Stokes equation is used, representing Stokes flow:

F u u      2   p dt d (1)
whereρ is the density, u the velocity, p the pressure, μ the dynamic viscosity and F is the sum of all the body forces. For natural convection, the body force F in ( 1) is given by

  0 C C f NC     g F (2)
whereβ is the compositional expansion coefficient, g is the gravitational acceleration, f is the liquid fraction, C the concentration of solute and C 0 the bulk concentration. In the case of forced convection, F FC is assumed to be a constant body force acting over the entire domain. Furthermore, due to the relatively small thickness, W of thin samples and low Reynolds number the flow between the plates can be assumed to be Poiseuille flow. By selecting a characteristic bulk mean velocity u the body force can be calculated from

2 2W FC u F   . ( 3
)
For TEMHD, the current density, J is given by a generalised form of Ohm"s law including an extra term accounting for

thermoelectric currents [16] B u E J      T S  (4)
whereσ is the electrical conductivity, E the electric field, S the Seebeck coefficient and B the DC magnetic field.

The thermoelectric currents interact with the magnetic field generating a Lorentz force given by

B J F   TE . ( 5
)
In all cases natural convection is present, hence for forced convection The numerical model simulates a 5 x 5 x 0.1mm 3 region of the solidification cell. The computational grid comprises cubes with a length of 5μm. Table 1 shows the material properties used in the simulation. Periodic boundary conditions are applied on the x faces normal to the thermal gradient representing an infinitely wide sample.

Table 1. Material properties used in the numerical model

Results and discussion

The numerical results for the three test cases are shown in figure 2 in three columns. The top row shows the velocity in μm/s, the bottom row the concentration of Ga in wt%.:

(i)When no magnetic fields are applied, natural convection is the only driver for fluid flow. Plumes of solute are generated by convective rolls close to the interfacethat draw enriched solute from the inter-dendritic region. In most cases, as the inter-dendritic region solidifies and the porosity decreases the convective rolls destabilise and the plumes migrate along the interface.

(ii) The second column shows the effects of the rotating magnetic wheel. Close to the interface the flow is purely by forced convection. Due to the reduction in porosity between the dendrites, the bulk mean flow is significantly larger than any inter-dendritic flow. The flow introduces several significant effects. The first is the preferential growth of secondary arms, which can be attributed to incident bulk concentration flow promoting growth. The second is the increase in primary arm spacing, which is a result of downstream enriched solute being passed from one tip to its neighbour stunting growth. Finally, plumes of solute are transported downstream and back into the bulk. (iii) The final case (which at this stage is purely theoretical) looks at TEMHD flow, where relatively high thermoelectric currents exist in the inter-dendritic liquid. Application of a 1T external magnetic field normal to the figure generates a Lorentz force, driving flow in inter-dendritic regions where there is a significant current. However as the porosity decreases the inter-dendritic flow becomes restricted. This creates a region of relatively high velocity that tracks the solidification front. The underlying mechanism is similar to forced convection, as this region of velocity transports liquid downstream. Depending on the concentration of the liquid, growth is either promoted or stunted. However, in contrast to the case of forced convection, the absence of currents in the bulk combined with electromagnetic damping gives no bulk mean flow. Moreover, electromagnetic damping slows the formation of plumes of solute. The inability to effectively eject solute into the bulk causes the inter-dendritic region to become more enriched compared to the other cases.

Figure 3 shows experimental results with no magnetic field and with forced convection from the rotating magnetic wheel. There is a reasonable agreement of the predicted mechanisms from the numerical analysis and the experimental observations for the two cases tested: The primary arm spacing has increased with convection and secondary arm growth is enhanced against the flow direction. A "saw tooth" solid front develops due to solute concentration ahead of tall dendrites and plumes of solute are suppressed.

Conclusions

This work demonstrates the ability to suppress the formation of solute plumes through the use of magnetic fields. The introduction of fluid flow by the magnetic field also changes the microstructure. Through selective design of the magnetic field it is conceivable that the formation of freckles can be prevented allowing for a more reliable method of casting for alloys with large density variations.

  of Ga-In25wt%.alloy in a Hele-Shaw cell with dimensions 25 Χ 35 Χ 0.15mm 3 was observed by X-ray radiography. The Hele-Shaw cell was cooled at the bottom by a Peltier cooler at a rate of 0.01K/s. An electric heater at the top with variable heating power was applied to maintain a thermal gradient of 1K/mm over the entire cell. A magnetic wheel was applied at the top of the cell to provide forced convection conditions. The sample is cooled from a molten state and at time t = 0s nucleation occurs and solidification of the microstructure propagates from the base of the sample to the top. A schematic of the experimental setup is given in figure1.

Figure 1 .

 1 Figure 1.Experimental setup. Left: X-ray radiography system. Right: Hele-Shaw solidification cell with electric heater, Peltier cooler and magnetic wheel.

Figure 2 .

 2 Figure 2.Numerical results showing microstructure morphology, velocity in μm/s (top) and concentration in wt% Ga (bottom) under various magnetic conditions. Left: No magnetic field, natural convection. Centre: Rotating magnetic wheel, forced convection. Right: Static transverse field, TEMHD convection.

Figure 3 .

 3 Figure 3.In situ radiographs during solidification of thin sample experiments showing microstructure morphology and concentration (%wt. Ga) in the melt. Left: Natural convection. Right: Forced convection (flow is from left to right).

Acknowledgments

The research is supported by the EPSRC (EPK011413/1) and the German Helmholtz Association in form of the Helmholtz-Alliance "LIMTECH".


K Dadzis

G Lukin

D Meier

P Bönisch

L Sylla

O Pätzold

Crystallization of gallium in a traveling magnetic field as a model experiment

Keywords: crystal growth, directional solidification, magnetic fields, model experiments, gallium

published or not. The documents may come   L'archive ouverte pluridisciplinaire

Introduction

The directional solidification process is used in the photovoltaic industry to produce large square silicon ingots with a weight up to 1000 kg. This process is performed in a crystallization furnace containing a square-shaped silica crucible surrounded by several heaters at the side or top and a heat sink at the bottom. Silicon raw material, typically in form of chunks, is placed in the crucible and melted. Then the heating power is adjusted to ensure directional solidification of the silicon melt starting from the crucible bottom. The solidification process has a strong impact on the ingot quality and is characterized by high physical complexity [1][START_REF] Dadzis | 9th International Conference on Fundamental and applied MHD[END_REF]. The alternating currents in the heaters usually generate Lorentz forces in the molten silicon which interact with buoyancy forces and cause an intense convection. The deformed temperature field in the melt results in a deflected phase interface which may have a significant influence on the flow pattern itself. This interaction process is continuously changing with the melt height which gradually decreases to zero. Numerical simulation is an efficient tool for the understanding and optimization of such complex phenomena especially if it is supported by model experiments to validate the numerical models. This contribution presents such small-scale model experiments using gallium as a model material and a traveling magnetic field (TMF). Pure gallium has a melting point of 29.8 °C, allows for an induction of Lorentz forces similarly to a silicon melt, and can be also solidified in a controlled manner [START_REF] Gau | [END_REF][4][5].

Experimental setup

Model experiments for a TMF-induced flow in a square-based melt container have been performed previously using GaInSn both in an isothermal setup [6] and with a vertical temperature gradient [7]. The present experimental setup (see Fig. 1) is particularly developed for the directional solidification of gallium. The sidewalls of the container are made of Macrolon with a thickness of 15 mm bolted with several screws in the corners. A cooler of aluminum serves as a bottom of the container. It has a thickness of 23 mm and contains a cylindrical cavity with a diameter of 80 mm, located 5 mm from the top surface and 10 mm from the bottom surface. Two water inlets are located at two opposite sides and two outlets at the other two sides. The heater on the top of the melt consists of two rectangular copper tanks glued together. The total thickness is 11 mm with walls of 5 mm on the melt side and 2 mm on the opposite side. Four inlets are located in the corners and two outlets at side centers. The heater and the cooler are connected to LAUDA thermostats with typical water flow rates of 3.3 l/min and 2.3 l/min and typical powers of 3.5 kW (heating) and 1.5 kW (heating)/ 0.18 kW (cooling), respectively. The surfaces of heater and cooler are electrically insulated using a Thermiflex foil of 0.07 mm thickness. There is a closed volume above the heater flushed with fresh argon to reduce the oxidation of gallium.

Temperature in gallium is measured through the sidewalls with two Type K thermocouples located 2 mm from the heater in the center and 2 mm from the cooler at the side wall. A commercial UDV measurement system DOP2000 from Signal Processing SA with an 8 MHz probe is used for measurements of the velocity profile and the position of the phase interface through a central opening in the heater. This opening is also occasionally used to mechanically measure the interface position. The phase interface shape is obtained from crystal height measurements at several positions after stopping the experiment and removing the heater (and in some cases also the melt).

Numerical model

The actual numerical model for 3D simulations has been already published in Refs. [1][START_REF] Dadzis | 9th International Conference on Fundamental and applied MHD[END_REF]. The 3D time-averaged Lorentz force induced by the TMF in the melt is calculated using the finite element package GetDP by solving the timeharmonic equations for the electric and magnetic potentials V and A. The electromagnetic model for the experimental setup was validated using magnetic field measurements. A geometric approximation was developed for the heater and cooler in form of massive plates with effective thicknesses of 4 mm and 8 mm, respectively, with a 2 mm gap to gallium. Electrical conductivities of 3.9•10 6 S/m for liquid 4.7•10 6 S/m for solid gallium (exhibiting a distinct anisotropy) were obtained. Other material properties have been summarized in Ref. [START_REF] Dadzis | 9th International Conference on Fundamental and applied MHD[END_REF]. The Lorentz force distribution is calculated for a fixed melt height of 38 mm and deformed together with the mesh in solidification calculations.

Coupled unsteady 3D calculations of the melt flow and phase interface are performed using the finite volume package OpenFOAM. The equations for incompressible flow (velocity u, pressure p) considering Lorentz forces F L and buoyancy forces (gravity g) in Boussinesq approximation as well as the equation for the temperature T are solved in the melt domain:

( ) ( ) g T T F u p u u t u L r r r r r r ρ β η ρ 0 - - + ∆ + -∇ =       ∇ ⋅ + ∂ ∂ , 0 = ⋅ ∇ u r , ( )
T T u t T c ∆ =       ∇ ⋅ + ∂ ∂ λ ρ r ,
where ρ, η, β, λ, c denote density, viscosity, thermal expansion coefficient, thermal conductivity, and heat capacity respectively. The heat conduction equation is solved in the crystal domain. Both domains are coupled with an isothermal phase interface which is moved/ deformed in each time step according to the local heat balance (Stefan condition) [1]. No turbulence model is used in flow calculation, the Reynolds number in the present setup is approximately Re=1400. The side walls are assumed adiabatic. The heater and cooler surfaces are described according to ( )

W T T p n T - = ∂ ∂ λ
with p the heat transfer coefficient and T W the thermostat temperature. Values of p=850 W/m 2 K for the heater and p=1400 W/m 2 K for the cooler were obtained from stationary temperature measurements [START_REF] Dadzis | 9th International Conference on Fundamental and applied MHD[END_REF].

Results and discussion

A typical experiment in the present study starts with a completely solidified gallium. The heater and cooler thermostats are set to T H =36.9 °C and T C =28.3 °C, respectively, which initiates a melting process at the top. After the remaining crystal height in the center reaches about 1 cm, the temperatures are switched to T H =31.2 °C and T C =23.6 °C, so that a solidification process starts. Fig. 2(a) summarizes the temperatures at the top and bottom of gallium as well as the phase interface position in the center for the case without a TMF (without melt flow). It can be seen that melting and solidification times for 6 cm of crystal height are both about 200 min, with a good agreement between experiment and simulation. Some deviations can be observed for the temperature curves:

• The simulation was started from a homogeneous temperature distribution in gallium while a small temperature gradient was applied in the experiment. This deviation has no significant influence on the following process. • The drop of the bottom temperature after switching to solidification is less steep in the experiment. This effect is caused by the limited cooler power and could be included in the simulation with a time-dependent T C value. • The top temperature is about 0.5 °C lower in the experiment. This deviation probably occurs due to the melt undercooling which was neglected in the simulation.

Measurements of the interface shape for the case without TMF indicated deviations from a flat surface up to about 3 mm, which is probably caused by the anisotropic thermal properties of solid gallium.

The previous experiment was repeated with a TMF up using a frequency of 16.6 Hz, phase shift of 60°, and current amplitude of 705 A in each coil. The resulting Lorentz force distribution is shown in Fig. 2 structure already known from similar experiments [6][7], but in this case the torus is broken in the corners. The vertical velocity profiles in Fig. 4(a) confirm a downward flow in the center. Note that reproducible velocity measurements at the central position were possible only during solidification and at large melt heights, when the velocity magnitude reached about 10 mm/s. Since the vertical temperature difference in the melt was about 0.3 K during solidification and 3.5 K during melting (see Fig. 4(b)), damping of the TMF flow by the buoyancy forces was much stronger during the melting stage.

The time-dependence of interface position in Fig. 2(b) shows that the melting time in the center is reduced due to the TMF flow to about 100 min while the solidification time remains approximately the same. The time-dependence and distribution of the temperature in gallium is qualitatively similar to the case without a TMF, see also Fig. 4(b). The most distinct effect of a TMF flow can be observed in the changes of phase interface shape. Fig. 3 demonstrates that at the end of melting the interface becomes concave, with a maximum deflection of 15 mm. The four corners exhibit a local convex deflection, and the whole interface shows a slight asymmetry in the experiment. This asymmetry is probably caused by the anisotropic crystal properties. Apart from that, the measurements agree well with the calculated interface shape. Note that the melt flow velocity during the melting was relatively weak reaching only about 2 mm/s in the central part, see Fig. 4(a).

Conclusions

It can be concluded that already relatively weak melt flows induced by time-dependent magnetic fields such as a TMF may lead to significant changes of the local melting rate and consequently a deformation of the phase interface. Such effects should be taken into account for silicon growth processes and can be efficiently investigated using unsteady 3D flow simulations validated in small-scale model experiments. A good agreement between experimental and numerical results was achieved in the present work.

Fig. 1 :

 1 Photo of the experimental setup without TMF coils (a); sketch of the setup (b).

  (d) and reaches a maximum force density of 40 N/m 3 . The 3D streamlines for a middle melt height in Fig. 2(c) generally indicate a toroidal flow (a) Simulation (b) Experiment Fig. 3: 3D interface shape with TMF up at the end of melting with a remaining crystal height of 15 mm in the center: numerical results (a) and experimental measurements at 15x15 points (b).

3 Fig. 2 :Fig. 4 :

 324 TMF up (c) TMF up (d) TMF up, F L MAX (cut) = 39.7 N/m Experiments and simulations for Ga melting/ solidification without TMF and with TMF up: top (T T ) and bottom (T B ) temperatures, crystal height (H C ) in the center (a,b) where experimental results are shown with symbols ◊; 3D flow streamlines (c) and Lorentz force distribution in vertical cross-section (d) for melt height H M =38 mm. Ga melting/ solidification: time-average velocity with TMF up (a) and temperature profiles without TMF and with TMF up (b) on the vertical axis (z=0 on crystal bottom) for various melt heights H M . Experimental results are shown with symbols ◊.

Acknowledgment

The authors would like to thank the Federal Ministry for the Environment (BMU) for the funding received within the grant 0325646A (project ENOWA).


Y Zhang

K Svynarenko

Q Zou

J Jie

T Li

Effect of rotating magnetic field and manganese on the formation of ironcontaining intermetallic compounds in Al-Si alloy

Keywords: Rotating magnetic field, Manganese neutralizer, Iron-containing intermetallic compound, Al-Si alloy

published or not. The documents may come

Effect of rotating magnetic field and manganese on the formation of iron-containing intermetallic compounds in

Al-Si alloy

Introduction

Al-Si alloys are the most used aluminium foundry alloys due to their excellent mechanical properties. Iron is well regarded as an unavoidable impurity in these alloys and known to be detrimental to the mechanical properties, especially the ductility [1] . Iron atoms can easily interfuse into the Al-Si alloys during melting and casting process with iron tools being used. On the other hand, a large amount of brittle intermetallic compound (IMC) will form at normal cooling rates employed in permanent and sand mold casting, as long as the iron content is above 0.7 pct [2] . Such phase always presents a acicular shape, and has a poor bonding with the matrix which results in a severe loss of elongation. It is therefore important to eliminate the harmful effect of iron containing IMCs [3] . The iron-containing IMCs appear in a great variety of shapes and sizes, among which the two most common phases have been designated as α-AlFeSi phase and β-AlFeSi phase [4,5] . The α and β phases can be distinguished by their characteristic morphologies and chemical compositions. The β-phase only exhibits a needle shape, and is always denoted as Al 5 SiFe or Al 9 Si 2 Fe 2 . By contrast, the α-phase appears in different shapes, such as Chinese script, fish bone, star, polygon or block, etc. Its chemical formula is usually expressed as Al 8 SiFe 2 , Al 12 Si 2 Fe 3 or Al 20 Si 2 Fe 5 . In conventional casting process, α-AlFeSi phase is metastable, it converts to primary β-AlFeSi phase, normally only acicular β-AlFeSi is present in the solidification structure. Manganese is an efficient neutralizer and commonly used to modify the acicular iron-containing IMC. Manganese atom can replace iron without changing the crystal structure, forming quaternary IMC [6] . Among the invariant reactions in Al-Fe-Mn-Si system, the one of some interest for Al-Si alloy is [7] :

Liq. + β-AlSiFe →Al + Si + α-AlSi(FeMn) (1)
By undergoing this reaction, the acicular β-phase converts to quaternary α-phase, which is less harmful and considered not to initiate cracks in foundry Al-Si alloys to the same extent as the acicular one. However, the replacement of β-phase by α-AlSi(FeMn) requires sufficient amount of manganese, and leading to the increased amount of IMCs, which is also disadvantageous to Al-Si alloys. Therefore, it is of special importance to find a method to neutralize the detrimental effect of β-phase, while reducing the required content of manganese. Application of external fields may be a potential way to alter the morphology or composition of the iron-containing IMCs. It has been reported that physical fields, such as ultrasonic field, electromagnetic field, etc., are successfully used to refine and modify the microstructure of Al-based alloys [8,9] . In the present study, the rotating magnetic field (RMF) and neutralizer manganese were complexly introduced into Al-12%Si-2%Fe melt. By means of the microstructure evolution and composition change of iron-IMCs, the effect of RMF was investigated.

Experimental Procedure

Starting materials consist of commercial purity Al (99.7%), pure Si (99.9%), pure Mn(99.9%) and Al-20 %Fe master alloy. All compositions quoted in this work are in wt.% unless otherwise stated. The Al-12%Si-2%Fe alloy was smelted in a resistance furnace at 900°C and kept for 1 h in order to fully fuse iron-compounds. After holding, different amount of manganese (Mn/Fe ratio = 0, 0.5, 0.8, 1.1 ) was added into the melt. Then, the melt was transferred into a preheated cylindrical graphite crucible (45 mm in dia. and 100 mm in height). When the temperature lowered to 850°C, RMF was applied until the ingot was completely solidified. The cooling rate was measured to be about 38 oC/min. The RMF of 50 Hz frequency was induced by a three-phase-three-pole magnetic generator. The voltage was set as 0 V, 40 V, 60 V and 80 V, with the corresponding magnetic flux density in the center of the crucible 0 mT, 12 mT, 18 mT and 24 mT, respectively. The ingots obtained were cut along the central vertical plane and grounded to examine the macrostructure. Small samples taken from the cross-section of ingot at 20 mm distance from the bottom were prepared for the microstructure observation by optical microscope MEF-4A. The electron probe microanalyzer (EPMA) was used to measure the chemical composition of IMCs.

Results

Figure 1 shows the macrostructure of Al-12%Si-2%Fe alloy smelted with different content of manganese.

The typical as-cast coarse acicular iron phase is presented in Fig. 1a, which can be observed by naked eye.

As shown in Fig. 1b and1c, with the increasing Mn/Fe ratio to 0.5 and 0.8, there is some granular iron IMCs found in the bottom of the ingot. The shape of particles suggests that they probably are manganese IMCs, especially that manganese is more powerful than iron in causing gravity separation [7,10] . However, lots of large acicular phase still can be observed in the section. When Mn/Fe ratio is 1.1, acicular inclusions are fully substituted by the granular phase. It can be concluded that the addition of manganese causes the morphological transformation of iron phase from needle to compact, and the increasing Mn content is beneficial for facilitating the transformation. Such results are consistent with earlier reports.

Fig. 1: Macrostructure of Al-12%Si-2%Fe-x%Mn alloy (x=0, 1.0, 1.6, 2.2) Figure 2 shows the influence of RMF and manganese on the microstructure evolution of iron-containing IMCs in Al-Si-Fe alloy. Without Mn and RMF, the iron phase is crystallized in an acicular shape, as mentioned above. The quantitative element analysis by EPMA (table 1) shows clearly that the acicular phase (highlighted by arrow 1) is β-Al 9 Si 2 Fe 2 . The RMF applied singly induces some changes to the morphology of IMCs reducing their size, rather than affects its composition. It is notable that the rod-like phase is still β-phase with the chemical formula Al 9 Si 2 Fe 2 . Figure 3 shows the comparison of the iron phase average size under different conditions, the data is calculated from more than fifty iron-containing IMCs for each condition, and based on more than five metallographs those are not totally displayed in Fig. 2. The size and length-width ratio of β-phase are reduced significantly by RMF. When the manganese is added (Mn/Fe ratio is 0.5 and 0.8) without the application of RMF, a number of star-like iron-containing IMCs of α-type (Table 1) appear in the microstructure (Fig. 2). However, the acicular intermetallics are still present in the matrix, although their amount decreases with increasing the manganese content. With the Mn/Fe ratio of 1.1, there is only star-like iron-containing IMC in the microstructure. The average composition of this phase at highlighted points 4, 7, 9 (Fig. 2) is similar. The content of manganese is close to that of iron, and the approximate compound chemical formula is Al 12 Si 2 Fe 1.5 Mn 1.5 . Following treatment by RMF results in an evident change in the alloy microstructure. Both, star-like and acicular compounds are replaced by the blocky ones. More important, when the manganese is added and RMF is applied, the trend in the IMCs morphology evolution in the case of Mn/Fe ratio 0.5 and 0.8 is similar to the case of Mn/Fe ratio 1.1. Furthermore, the slight changes in the iron phase morphology can be observed with different voltage of RMF. With the increasing input voltage, the compounds shape trends toward hexagonal with smooth edges. The composition of the iron phase obtained with various concentrations of manganese differs considerably. When Mn/Fe ratio is 1.1, the ratio of manganese and iron content in the hexagonal blocks is nearly 1. The approximate chemical formula can be expressed as Al 12 Si 2 Fe 1.5 Mn 1.5 , similar to the star-like phase formed without RMF. When the Mn/Fe ratio is 0.5 or 0.8, the content of Mn in the blocky compounds (arrowed as 5 and 8 in Fig. 2) is only half of iron amount. The approximate chemical formula of this phase is Al 12 Si 2 Fe 2 Mn 1 . It indicates that the application of RMF can facilitate the formation of α-AlSiFeMn phase, as well as its transformation to hexagonal blocks even at lower manganese content. Therefore, with the application of RMF the consumption of neutralizer can be reduced and the amount of iron-containing IMCs in modified alloys can be decreased. In the case of RMF applied without addition of manganese, the electromagnetic stirring most likely to be responsible for the transformation of β-phase from acicular shape to the rod-like. It is well known that RMF induces fluid flow in the treated melt, leading to thermal and solute transfer. When RMF is applied, there is a Lorentz force generated in the melt [11,12] , the azimuthal component of which is written as F L . A schematic illustration of this magnetic force and flow direction of a melt under RMF is shown in Fig. 4. In the cross-section, the Lorentz force has a tangential direction, and thus the liquid metal mainly exhibits a primary motion in the form of a swirl. This electromagnetic stirring is useful in assisting dendrite fragmentation and abscission of secondary dendrite arms during solidification [11] . For this reason, the strong stirring is considered to fragment the brittle acicular β-phase. With the increasing voltage, the magnetic force F L and the corresponding magnetic flux density will increase. The average length of βphase therefore reduces along with increase in stirring effect. In addition, rotating followed by the fluid flow during the solidification is also useful to the inhibition of β-phase growth. These should be the reasons for the change in the morphology of β-phase. According to the microstructure of alloy, the influence of RMF on the morphology and type of ironcontaining IMCs depends on the presence of manganese. Under conventional casting condition, the acicular iron phase can be neutralized only by the additions of sufficient amount of manganese (Mn/Fe ratio is 1.1 in this study) which converts the β-Al 9 Si 2 Fe 2 into the more compact star-like α-Al 12 Si 2 Fe 1.5 Mn 1.5 . But at lower manganese concentrations (Mn/Fe<1.1), only part of β-phase gets neutralized. Some star-like α-Al 15 Si 2 Fe 1.5 Mn 1.5 appear by undergoing reaction 1. At the same time, the formation of α-phase consumes most manganese present in the melt and shifts the local chemical composition. As a result, part of iron IMCs grow to α-Al 15 Si 2 Fe 1.5 Mn 1.5 due to manganese segregation, while in the regions depleted with manganese, the more stable β-phase is formed. With using RMF, a forced convection is generated in the melt as soon as it is applied. The presence of the electromagnetic driven flow promotes the uniform distribution of alloying elements, leading consequently to the componential homogenization. The manganese segregation during neutralization is thus restrained. By the contribution of RMF, each piece of β-phase platelet can be provided sufficient manganese for the transformation to α-AlSi(FeMn). Since the manganese concentration in the melt is lower, the product is α-Al 12 Si 2 Fe 2 Mn 1 rather than α-Al 12 Si 2 Fe 1.5 Mn 1.5 . Therefore, the facilitation of α-AlSiFeMn phase formation under RMF should be related to the solute homogenization by electromagnetic stirring.

Conclusions

Effect of RMF and neutralizer manganese on the morphology and composition of AlFeSi IMCs formed in the Al-12%Si-2%Fe alloy were studied. The main conclusions can be formulated as following:

(1) The manganese addition causes the transformation of β-Al 9 Si 2 Fe 2 IMC to the α-α-Al 12 Si 2 Fe 1.5 Mn 1.5 IMC with subsequent changes in morphology of iron phase from acicular to star-like. The increasing manganese content is beneficial for the converting, and the total transformation is achieved when Mn/Fe ratio is 1.1.

(2) In the absence of neutralizer, the RMF only affects the size and morphology of β-Al 9 Si 2 Fe 2 , single RMF makes the iron phase crystallized in rod-like. When the manganese is introduced, the application of RMF facilitates the formation of Al 12 Si 2 Fe 2 Mn 1 at lower Mn/Fe ratio (0.5 and 0.8).

Fig. 2 :

 2 Fig. 2: Microstructure of Al-12%Si-2%Fe-x%Mn alloy (x=0, 1.0, 1.6, 2.2) smelted with RMF of different voltageTable 1 Composition analysis of the iron phases in Fig.2 by EPMA (mol.%) Point Al Si Fe Mn Average chemical formula

5 Fig. 3 :Fig. 4 :

 534 Fig. 3: Morphological analysis of theiron-containing phases with RMF and Mn Fig. 4: Schematic illustration of the Lorentz force and flow direction under RMF on the top view, (a) Lorentz force, and (b) flow direction DiscussionIn the case of RMF applied without addition of manganese, the electromagnetic stirring most likely to be responsible for the transformation of β-phase from acicular shape to the rod-like. It is well known that RMF induces fluid flow in the treated melt, leading to thermal and solute transfer. When RMF is applied,

Table 1

 1 Composition analysis of the iron phases in Fig.2by EPMA (mol.%)

	Point	Al	Si	Fe	Mn	Average chemical formula
	1	67.126 16.763 16.111	0	β-Al 9 Si 2 Fe 2
	2	67.931 16.354 15.715	0	β-Al 9 Si 2 Fe 2
	3	65.308 19.012 14.222 1.458	β-Al 9 Si 2 Fe 2
	4	71.395 10.371 10.104 8.131	α-Al 12 Si 2 Fe 1.5 Mn 1.5
	5	68.647 12.291 12.652 6.410	α-Al 12 Si 2 Fe 2 Mn 1
	6	65.120 18.728 14.906 1.245	β-Al 9 Si 2 Fe 2

Acknowledgement

The authors gratefully acknowledge the support of China Postdoctoral Science Foundation (2015M570246).


F Cao

T M Wang
email: tmwang@dlut.edu.cn

F F Yang

H J Kang

T Q Xiao

T J Li

Direct observation of solutal convection during solidification of Sn-50wt.%Pb alloy under traveling magnetic field

Keywords: solidification, solute convection, traveling magnetic field, synchrotron radiation

Direct observation of solutal convection during solidification of Sn-50wt.%Pb alloy under traveling magnetic field

Introduction

It is well know that the convection in a solidifying melt can significantly influence the solute distribution directly in metal alloys and hence the mechanical properties of the materials [1][2][3]. Consequently, a precise mastering of the solute convection in the solidifying melt is essential to improve the materials performance. Application of the external physical field, such as electric field [4,5], magnetic field [6][7][8] and ultrasonic field [9,10], has been demonstrated to be an effective method for achieving high quality castings. Among the external physical field, the magnetic field offer an efficient way for a contactless influence on the convective transport of solute in the unsolidified melts. However, majority of the related studies are mainly restricted to a post-mortem analysis and cannot reveal the dynamic information. With the development of the third-generation synchrotron radiation facility, synchrotron X-ray radiography has become an powerful tool for in-situ and real-time observation of the solidification of opaque metal alloys in the recent years [11][12][13][14][15][16]. So, this imaging technique can also be applied to study the effect of magnetic field on the solidification of alloys directly. At present, only a few studies [17][18][19][20] have been reported to study the effect of electromagnetically driven melt convection on the solute profiles and the dendrite morphology using X-ray radiography, and no study on the effect of TMF was reported.

In this paper, we focus on the visualization of the solute distribution and the dendritic growth during the bottom-up solidification of Sn-50wt.%Pb alloy using synchrotron X-ray radiography. Based on the in-situ and real-time observations, we investigate the effect of solutal convection on the redistribution of solute profile and the dendrite morphology with and without a TMF in a solidifying melt.

Experimental

The experiment were carried out at beamline BL13W1 of Shanghai Synchrotron Radiation Facility (SSRF). A binary alloy with a composition of Sn-50 wt.% Pb was prepared by melting high purity Sn (99.99%) and Pb (99.99%) in an alumina crucible and casted into a cylindrical stainless steel mold. A well ground and polished sample (10×20 mm 2 and 120 μm thick) was encapsulated between two ceramic plates. A hollow polytetrafluoroethylene (PTFE) sheet was also placed between the two ceramic plates, and used to fix the sample.

The synchrotron X-ray imaging technique was used to study the effect of TMF on solute convection in solidifying Sn-50wt.%Pb alloy. The incident monochromatic X-ray was passed through the sample with an energy of 26 keV. The time sequenced images were recorded by a charge coupled device (CCD) camera with a satisfying spatial resolution (pixel size 3.7×3.7 μm). The exposure time per frame was 3-4 s.

The schematic diagram of synchrotron radiation imaging experimental setup is shown in Fig. 1. The sample cell was placed in close contact with both upper and lower plate heaters which could control the temperature independently. The temperature along the sample cell was measured by two embedded K-type thermocouples 1 cm away from each other. The mean temperature gradient over the sample was G = 6.3 K cm -1 for all experiments. The average cooling rate of the sample was R = 5 K min -1 . During the solidification, the dendrite front grew from bottom to top (antiparallel g) unidirectionally. The TMF was applied after a certain time when the dendrite front has reached about one second of the field of view. The TMF is generated by means of applying out-of-phase alternating-current to the TMF generator which was placed at the bottom of the lower heaters.

Results and discussion

Fig. 2 shows a sequence of in-situ radiographs recorded during the solidification of Sn-50wt.%Pb alloy with and without a TMF. Fig. 2a-c show the solidification of Sn-50wt.%Pb alloy without a TMF, and a natural convection is formed during this process. The dark dendritic network corresponds to the primary Pb dendrites which are grow from bottom to top. The Sn-rich zones can be identified in the interdendritic regions and in the vicinity of the dendrite front as a result of solute rejection. The solute rejected at the solid-liquid interface is less dense as compared with the initial composition of the melt. Thus, the melt density difference in different areas provokes the formation of ascending plumes containing Sn-rich solute. Many small plumes arise at the early stage of the solidification, and then the plumes are well developed. The plumes span a distance of several millimeters and produce a long range diffusion of solute towards the melt region. Similar phenomena are also observed by Shevchenko et al. [17,20] in the solidification of Ga-In alloys. Moreover, the growth of dendrites are affected by several small crystals (grains 1 and 2 in Fig. 2b) ahead of solidification front. But finally those small crystals are blocked by the overgrowing dendrite side arms. The solute distribution can be reflected by the evolution of the gray level which related to X-ray transmitted intensity. Fig. 3a displays the gray level distribution in the melt measured at position of horizontal line A marked in Fig. 2c. It is show that the gray level distribution (i.e. Sn concentration profile) along the solidification front is inhomogeneous corresponding to the plumes pattern, which can be explained by the buoyancy driven convection that the ascending plumes containing Sn-rich solute is accompanied by a downward flow of Sn-poor melt in the intermediate space. Fig. 3b shows the gray level distribution in the melt ahead of the solid-liquid interface at positions of longitudinal lines B and C marked in Fig. 2c. The solute distribution and transportation at the solidification front have an influence on the growth of Pb dendrites. The advancement of the dendrite front at the plume positions is suppressed and the dendrite tip positions fall behind the neighboring regions where no plume exist, as shown in Fig. 2a-c.

Conclusions

The solute distribution and the dendritic growth during the bottom-up solidification of Sn-50wt.%Pb alloy under a TMF were investigated by the Synchrotron X-ray radiography. The buoyance driven development of the plumes containing Sn-rich solute are directly observed. The advancement of the solidification front at the plume positions is decelerated and the dendrite tip positions fall behind the neighboring regions where no plume exist. A forced melt flow is induced when the TMF was applied. Preferential growth of the secondary arms is observed at the incoming flow sides of the primary dendrite arms, whereas the growth of the secondary arms at the opposite sides of the primary dendrite arms is suppressed due to the high Sn solute concentration. Besides, the dendrites remelting and fragmentation due to the solute enrichment are also observed. But the flow induced mechanical fragmentation is not observed directly in the present study.

Fig. 1 :

 1 Fig. 1: Schematic of synchrotron radiation imaging experimental setup.

Fig. 2 :

 2 Fig. 2: Sequence of in-situ radiographs recorded during the solidification of Sn-50wt.%Pb alloy with and without a TMF. (a)-(c) Solidification without a TMF; (d)-(f) solidification under the influence of a TMF.

Fig. 3 :

 3 Fig. 3: (a) Gray level distribution in the melt measured at position of horizontal line A marked in Fig. 2c; (b) gray level distribution in the melt ahead of the solid-liquid interface at positions of longitudinal lines B and C marked in Fig. 2c. Fig. 2d-f show the change of concentration field and the evolution of dendritic structure under the influence of TMF. A forced melt flow is induced ahead of the solidification front when the TMF was applied. As a consequence, the welldeveloped upright ascending plumes became unstable and the bottom of the plumes tend to deflect to the right, as shown in Fig. 2d. The plume denoted by the green arrow is seriously inclined and finally disappeared. The TMF induced melt convection ahead of the solidification front facilitates the solute transportation laterally and reduces the local fluctuations of solute concentration to some extent. As shown in Fig.2e-f, preferential growth of the secondary arms (denote by the orange arrows) is observed at the incoming flow sides of the primary dendrite arms. While the growth of the secondary arms at the opposite sides of the primary dendrite arms is suppressed due to the high Sn solute concentration. Similar dendrite growth behaviors are also captured by Shevchenko et al[21] in the solidification of Ga-In alloys. Meanwhile, the growth of Pb dendrites causes an accumulation of rejected Sn in the interdendritic zone in the process of solidification. The solute pile-up reduces the local undercooling and promotes a partly remelting of the dendritic structure, as shown in Fig.2f (red circles). As a consequence, small pieces of fragments detached from the dendritic network and fall into the mushy zone. Besides, forced flow induced mechanical fragmentation is not observed directly in the present study.

Acknowledgements

The authors gratefully acknowledge the supports of National Natural Science Foundation of China (Nos. 51274054, U1332115, 51271042, 51375070, 51401044), the Key grant Project of Chinese Ministry of Education (No. 313011), the Science and Technology Planning Project of Dalian (Grant No. 2013A16GX110), and the Fundamental Research Funds for the Central Universities. The authors wish to thank all the staff members of the BL13W1 beamline of SSRF and 4W1A beamline of Beijing Synchrotron Radiation Facility (BSRF) for corresponding experiments and discussion.


S Pavlovs

A Jakovics

V Sushkovs

B Nacke

Numerical study of turbulent flow and thermal field in industrial electrotechnological devices with combined power supply

Keywords: combined inductive and conductive power supply, turbulent flow, thermal field, LES study

The paper presents the numerical 3D models for computations of turbulent hydrodynamic and thermal fields for the electrotechnological devices with the combined power supply: conductiveover the submerged or non-submerged electrodes with direct current (DC); inductivewith the side inductor, the source of travelling magnetic field (TMF). The thermal field distribution and the overheating zones are considered for conditions, when the heat flux is supplied to the melt over the arc spot, which located under non-submerged or submerged tip of the top electrode. The structure and intensity of the melt circulation is discussed for the cases of high and low conductivity of melt.

Introduction

The current paper is a continuation of numerical study of the 3D physical fields in the electrotechnological magnetohydrodynamic (MHD) devices with the combined power supply: inductive by the inductor and conductive through the electrodes; the main results are presented in [1,2]. Some examples of the MHD devices are electrical arc furnaces (EAF), ladle furnaces (LF), plasma furnaces (PF), etc. The purpose of research is the application of developed 3D models for analysis of various technological regimes in order to obtain a desired quality of melts and alloys. The melt circulation [1] is a result of the combination of electro-vortex convection (EVC) and electromagnetic convection (EMC). The cross effects of the interaction between the current and a magnetic field produced by different alternating current (AC) sources affect mainly the pattern and intensity of the resultant flow and may cause rotation. The temperature field [2] in a turbulently flowing melt is modelled according to the thermal balance of heat exchange at the melt boundaries and the Joule heat volumetric sources produced by different types of AC power supply. The current paper is concerned with the numerical computations of a temperature field and a melt circulation in MHD devices with combined power supply (Fig. 1), which widen the application of the developed 3D models: • conductive -DC is supplied through the top (non-submerged or submerged) and the bottom electrodes • inductive -AC is supplied by the side inductor, the source of upwards travelling magnetic field.

Peculiarities of electromagnetic (EM) field computations

In the case of combined power supply the numerical solutions of the Maxwell equations must be found separately for the conductively supplied DC (over electrodes) and the inductively supplied AC (with inductor). The computations have been performed with ANSYS Multiphysics 14.0 using a static and a harmonic analysis accordingly. For approximation of the model geometry (Fig. 1) the element SOLID97 is used. The equations (real and complex accordingly) are solved with the direct method. The total number of equations is ~1.8 million.

The density of time-averaged total Lorentz force EM f  is found according to the superposition principle: The distributions of the total Lorentz force components and the total Joule heat are computed by means of the summation of corresponding distributions, obtained during the EM field computations, performed for both types of power supply. As these two sets of the results are obtained at the different meshes, the summation operation of Lorentz force and Joule heat for the different sources is performed in ANSYS CFX 14.0 with application of the build-in tools of interpolation to the mesh, which is used for the computations of HD and thermal fields. The mentioned above approach differs from referenced computations, which have been performed only for a single source of power, supplied over the DC electrodes; examples are chosen for several types of industrial equipment and processes -EAF [3,4], vacuum arc (VAR) [5] or electro-slag remelting (ESR) [START_REF] Kharicha | 9 th Int. Symposium on Liquid Metal Processing and Casting[END_REF], submerged arc furnaces (SAF) [START_REF] Wang | [END_REF].

  ind AC ind AC cond DC cond DC EM B j e B j f * 2 1           (1)

Peculiarities of thermal field computations

The thermal field modelling is performed only for the melt (Fig. 1 (b,c)) with the following assumptions concerned with melt heating during conductive power supply through the top electrode: • in the case of the non-submerged top electrode: an electric arc is burned between the electrode and the arc spot zone at the melt top surface; • in the case of the submerged top electrode: an electric arc is burned between the tip of electrode and melt; • the area of the spot (for non-submerged electrode) or the area of the tip (for submerged electrode) are equal to the area of the electrode horizontal cross-section; • the heat flux from the electrical arc is supplied to the melt over the spot (for non-submerged electrode) or over the tip of electrode (for submerged electrode). The thermal boundary conditions are determined for the following surfaces of the melt (Fig. 1 (b,c)):

• for the top surface radiative zone with the surface rad S the radiation heat flux rad q is determined;

• for the thermally insulated side and bottom solid wall with the surface solid S of the melt vessel the convective heat exchange flux conv q is determined;

• in the case of the non-submerged electrode: for the surface spot S the heat flux spot nonsub q from the arc directed to the melt is determined:

spot nonsub spot S melt q n T        spot cond melt ind melt solid conv rad rad spot nonsub S Q Q S q S q q       (2)
where the value of heat flux spot nonsub q is found from the initial thermal balance.

Q S q S q q        el sub tip el tip q a q    el sub tip el side q a q   1 (3)
where the value of the total heat flux el sub from the electrode is found from the initial thermal balance. The total surface of the electrode is

  K m W  2 .

Computational results

Maximum

Conclusions

The overheating zones' locations correspond to the surfaces of (non)submerged electrode, where the heat fluxes are supplied to the melt. The overheating temperature values and the temperature maxima locations depend on the melt flow intensity and pattern. In the case of high conductive melt the electromagnetic convection is prevailing. The intensity of the thermogravitational convection is comparable with the intensity of the electro-vortex convection only in the case of low conductive melt.

Fig. 1 :

 1 3D models of MHD device with top and bottom DC electrodes and side inductor, the source of upwards TMF: (a) structured mesh; AC phases in inductor; (b,c) thermal fluxes for non-submerged and submerged electrode.

  density, supplied over the electrodes, and cond DC B  is an induction of self magnetic field of the conductive DC (indexes 'cond' and 'DC'); ind AC j  is an amplitude value of a current density and ind AC B *  is a conjugate value of magnetic induction in case of the complex representation of quasi-stationary EM field, produced by the inductor with AC (indexes 'ind' and 'AC'). The density of total Joule heat EM Q is the sum of Joule heat due to conductive cond melt Q

•

  in the case of submerged electrode: for the surface el tip S the heat flux el tip q from the arc directed to the melt is determined as well as for the side surface el side S of the heated electrode the heat flux el side q

T

  The thermal parameters, which are used in boundary conditions (in details are written in[2]), are the following: =330 K temperature values are identical for all models; • the areas: spot S ~0.58 m 2 (non-submerged electrode); transfer coefficient at the vessel surfaces with the thermal insulation,

Fig. 2 := 6 . 7 •

 267 Fig. 2: System with nichrome (