The processing and properties of heavily cold worked directionally solidified Ni-W eutectic alloys
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INTRODUCTION
CONSIDERABLE interest has been evidenced recently on the manufacture and properties of metal matrix composites. For the most part current efforts are focused on artificial composites, that is, on those consisting of a metal matrix in which are imbedded strong particles or fibers of a second phase. Because of the complexities associated with their manufacture, such as fiber alignment and thermal treatment to effect matrix-reinforcement bonding, these materials are expensive. Heavily cold worked two phase metallic alloys constitute a subclass of metallic composites, one that can, in a sense, be considered a natural composite. These materials possess inherent economic advantages vis-a-vis the artificial composites described above. This arises because they are typically produced by well-characterized initial primary (e.g., casting) and secondary (e.g., drawing) fabrication techniques. Copper-niobium alloys provide a simple example. L2 Alloys of them can be cast and if the volume fraction of niobium is less than approximately 20 pct, the as-cast structure consists of isolated Nb dendrites contained within a continuous copper matrix. Subsequent wire drawing, or a like process, elongates the dendrites to an extent comparable to that of the material as a whole. The final result is a fibrous composite of (in this case) Nb filaments within a ductile face-centered cubic matrix. Lamellar-like composites can be made similarly. 9.4 This morphology obtains when the initial fabrication process produces continuity within both phases, and this is maintained during the cold working sequence. Properties of materials manufactured thusly are also interesting. The aforementioned Cu-Nb alloy can serve as a precursor for the production of filamentary Nb3Sn superD.G. KUBISCH, formerly Graduate Student, Department of Metallurgical Engineering, Michigan Technological University, Houghton, MI, is Senior Metallurgist, Wisconsin Centrifugal Inc., Waukesha, WI. T. H. COURTNEY is Dean of the Graduate School and Professor of Metallurgical Engineering, Michigan Technological University, Houghton, MI 49965. Manuscript submitted July 8, 1985. METALLURGICAL TRANSACTIONS A
conducting composites via a variant of the bronze process. 5-8 Likewise, composites based on silver and copper offer potential as high strength-high conductivity metals. These materials also manifest interesting mechanical properties. 9 Their strengths are typically well in excess of those expected on the basis of a rule-of-mixtures estimate which considers the strain hardening attendant to composite manufacture. Moreover, while fracture toughness data have not been generated for these materials (a result of their small size), measured tensile reductions in area are appreciable. Thus this in situ mechanical fabrication technique offers the possibility of producing high strength materials also having good toughnesses. Material's strength in excess of the rule-of-mixtures estimate depends on several factors including the material combination, the deformation strain, a
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