Severe Plastic Deformation as a Means of Producing Ultra-Fine-Grained Net-Shaped Micro Electro-Mechanical Systems Parts
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FABRICATION of miniaturized parts, particularly components for biomedical devices or microsystems such as MEMS, requires careful scaling of their internal structures. This calls for ultra-fine-grained (UFG) alloys as materials of choice. Indeed, UFG materials can fulfill two conditions at the same time: (1) that the average grain size be smaller than the smallest dimension of the structural component and (2) that the grain size be small enough to ensure sufficiently high strength and fracture toughness. Condition (1) implies that reproducible properties of the component are warranted due to averaging over a large number of grains (e.g., over the thickness of a thin film, the cross section of a wire or a tooth of a cog-wheel), while condition (2) is an expression of the fact that strength and fracture toughness are generally improved on grain refinement. Among the grain refinement techniques, severe plastic deformation (SPD) has advanced to the most promising one.[1] A significant body of literature has emerged over the past decade, cf. Reference 2 and references therein. The arguably most popular SPD method, equal channel angular pressing (ECAP),[3] has been shown to produce Y. ESTRIN, Professor, is with the ARC Centre of Excellence for Design in Light Alloys, Department of Materials Engineering, Monash University, Clayton, 3800 Victoria, Australia. Contact e-mail: yuri. [email protected] M. JANECEK, Senior Lecturer, is with the Department of Physics of Materials, Charles University, CZ-12116 Praha 2, Czech Republic. G.I. RAAB, Senior Researcher, and R.Z. VALIEV, Professor and Scientific Director, are with the Institute of Physics of Advanced Materials, Ufa State Aviation Technical University, Ufa 450000, Russian Federation. A. ZI, Research Assistant, is with the Institute of Materials Science and Engineering, Clausthal University of Technology, D-38678 Clausthal-Zellerfeld, Germany. This article is based on a presentation made in the symposium entitled ‘‘Ultrafine-Grained Materials: from Basics to Application,’’ which was held on September 25–27, 2006 in Kloster Irsee, Germany. Article published online June 2, 2007. 1906—VOLUME 38A, SEPTEMBER 2007
submicrometer scale grain structure in numerous metallic materials.[4,5] Average grain sizes in the range of 50 to 300 nm are not uncommon in ECAP processed materials. In the quest for developing nanostructured materials for structural applications, numerous researchers are looking for the way to upscale the known ECAP techniques and experimental rigs. Rarely have there been attempts to downscale the process with a vista of manufacturing miniaturized parts. An interesting example of using an ECAP processed material for producing microgears was recently presented by Kim and Sa.[6] These authors have demonstrated the viability of microextrusion of ECAP preprocessed Mg alloy AZ31 using a millimeter-scale extrusion die as a way of manufacturing microgears. Zi et al.[7] have suggested downscaling of the ECAP process itself in order to produce severely deformed aluminum
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