Strength and electrical conductivity of deformation-processed Cu-15 Vol Pct Fe alloys produced by powder metallurgy tech
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INTRODUCTION
R E C E N T research tl] on deformation-processed Curefractory metal alloys, Cu-X, where X is 15 vol pct Nb, Ta, or Cr, has demonstrated that these alloys have an outstanding combination of strength plus electrical conductivity. This conclusion is demonstrated in Figure 1, which compares ultimate tensile strength vs electrical conductivity of these three alloys to the best commercial alloy, C17510, t2] which is a Cu-Be-Ni alloy. (Note: The alloy has been given a special thermomechanical process, sometimes called TMT, to optimize properties, and the reported yield strengths have been increased 10 pct here as an estimate of tensile strength.) The deformationprocessed Cu-X alloys were all prepared employing large amounts of axially symmetric deformation of the cast alloy. The as-cast precursor billets were annealed and slow cooled to remove the X element from solid solution in the Cu, thereby optimizing the conductivity of the Cu matrix. In all of the above alloys, the X component is a bodycentered cubic (bcc) metal with very limited solid solubility in the Cu phase and a flow stress similar to pure Cu. The bcc structure results in the development of a ribbon morphology in the X filaments which form from the as-cast X dendrite arms during the deformation. It is believed t3~ that this ribbon morphology enhances the strength of these alloys relative to systems with cylindrical fiber morphologies. The low solubility allows the conductivity of the Cu phase to remain high, and the similarity of flow stresses between the Cu and X phases allows large coreductions of the X and Cu phases without the need for annealing. Annealing treatments of the heavily deformed microstructure are detrimental to strength because of filament coarsening. It has long been realized [4,5,6j that Fe would be an exG.A. JERMAN, formerly with the Department of Materials Science and Engineering and Ames Laboratory, Iowa State University, is with NASA, Marshall Space Flight Center, AL 35812. I.E. ANDERSON and J.D. VERHOEVEN axe with the Department of Materials Science and Engineering and Ames Laboratory, Iowa State University, Ames, IA 50011. This article is based on a presentation made in the symposium ~I-Iigh Performance Copper-Base Materials" as part of the 1991 TMS Annual Meeting, February 17-21, 1991, New Orleans, LA, under the auspices of the TMS Structural Materials Committee. METALLURGICAL TRANSACTIONS A
cellent choice for the X component in these deformationprocessed alloys. In addition to the economic advantage of Fe-Cu, the phase equilibria of Fe-Cu is similar to that of Nb, Ta, and Cr in Cu. Iron is also bcc at room temperature, and experiments have shown t5'61that the flow stress of Fe is sufficiently similar to Cu that cast Cu-Fe alloys may be drawn extensively at room temperature without breakage. Experiments with deformationprocessed Cu-Fe alloys have not, however, been successful in obtaining comparable strength-conductivity properties, as is demonstrated by the data from References 4 and 5 shown on Figure 1. It has p
