Elsevier

Acta Materialia

Volume 53, Issue 2, 10 January 2005, Pages 375-381
Acta Materialia

Control of macrostructure in deformation processing of metal/metal laminates

https://doi.org/10.1016/j.actamat.2004.09.033Get rights and content

Abstract

A study was carried out on model systems deformed under plane-strain. Finite element analysis was used to examine continuously and discontinuously layered models, in which the reinforcement to matrix flow stress ratio, rs, was varied within the range 1.5 < rs < 10. It was found that, for homogeneous refinement of continuously reinforced laminates, the critical value of rs is approximately 2. This value, valid for the ideal plastic case, can be increased to a maximum value of rs ≈5 with work hardening. For discontinuously layered systems, similar results were found. It is therefore concluded that macrostructural control is possible in metal/metal systems either in the form of homogeneous refinement of the continuous structures or in the form of structures with thin, long, closely spaced reinforcements, provided that the flow strength of the reinforcement is not more than five times that of the matrix.

Introduction

The deformation behaviour of two contiguous, ductile phases has been of interest at a variety of length scales [1]. The interest here stems from the dependence of the nature of the mechanical response of the system on the length scale [2], as well as from the associated change in microstructure [3], [4], [5]. At the coarse scale (i.e., the deformation of clad or sandwich metals), the form of macrostructural control is confined to maintaining the continuity and uniformity of the layered structure [6], [7]. At the fine scale, (i.e., in situ composites and metallic multilayers [8], [9], [10]), heavy deformation is an integral part of the processing and a requirement to develop high-strength. Consequently, the scope of macro/microstructural control is much wider. Here, the interest focuses on nanoscale structures produced in the final stages of cold working [8], [9], [10], but how and when these fine scale structures evolve depends to a large extent on the mode of structural evolution at earlier stages of deformation processing. The current work deals with the problem of structural evolution at the continuum level, and as such it is applicable to structural evolution of deformed clad or sandwich metals and to that of metallic multilayers at the initial stages of working.

When metallic multilayers at the length scale (i.e., interlayer distance) of a fraction of a millimetre are deformed, changes that occur in macrostructure follow mainly two patterns. In one, the continuity of the layers is preserved and the structure is refined in accordance with the overall macroscopic strain imposed on the system. In the other, the reinforcing layers neck and rupture into lamellae, which transform the material into a continuous matrix with hard embedded lamellae. In the latter case, the structure after deformation is similar to that of particulate reinforced composites.

The current work follows a series of studies [11], [12], [13] on deformation of metal/metal laminates and addresses the prospect of developing controlled macrostructures. The main parameter under study is the flow strength of the reinforcement relative to the matrix. The study aims to determine conditions which would enable the production, via deformation processing, of refined continuous structures. For discontinuous structures, the aim is to identify conditions, again in terms of the relative flow strength, which would lead to macrostructures with thin, long, closely spaced reinforcements.

Section snippets

Procedure

Deformation of the model laminates was studied by finite element analysis using the software package ANSYS. Continuously and discontinuously reinforced structures were examined. For continuous structures, a single reinforcing layer placed in the mid plane of the matrix was used. A model having a single reinforcing platelet was used in the discontinuous system, again placed in the midsection. The models, illustrated in Fig. 1, are two-dimensional since the deformation is plane-strain. Here

Continuous reinforcement

In continuously reinforced systems, four strain hardening cases were considered; with n = 0, 0.1, 0.3 and 0.5. The rs value was increased systematically from rs = 1.5, 2, 3, 5, etc. Variations of SAF values are shown plotted in Fig. 2(a)–(d).

It is seen that when the strength of reinforcement is close to that of the matrix, i.e., up to rs = 2, SAF remains less than 2, implying that the deformation is homogeneous. Periodic necking along the length of the reinforcement (i.e., multiple necking) occurs,

Discussion

Although, the observations made above refer to model systems incorporating a single reinforcement, the results are considered to be valid for multilayered laminates. As mentioned above, the models given in Fig. 1 should be treated as a representative portion of more voluminous multilayered systems.

For continuously reinforced systems, the predictions reported above are in good accord with previous observations [11], [12], [13]. In these studies involving Al–steel, Al–Zn and Cu–W laminates,

Conclusion

In this study, an investigation was performed into deformation processing of metal/metal laminates so as to develop controlled macrostructures. The main parameter under study was the strength of the reinforcement relative to that of the matrix, rs. The flow stress of both matrix and reinforcement were described by σ = n, where n is the strain hardening exponent and K is a constant. The main conclusions of the current study are as follows.

For continuously reinforced systems, homogeneous

Acknowledgement

Financial support for this work is provided by TÜBİTAK with project number MİSAG-67 which the authors gratefully acknowledge.

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