Strength and conductivity of Cu-9Fe-1.2X (X = Ag or Cr) filamentary microcomposite wires
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NTRODUCTION
MICROCOMPOSITES fabricated by mechanical working of ductile two-phase mixtures prepared by various techniques have been the subject of considerable research.[1–7] Tensile strengths greater than those predicted by a rule of mixtures are observed in heavily cold-worked microcomposites. The tensile strengths of deformation-processed microcomposites have been shown to correlate with filament spacings, leading to a Hall–Petch type relationship.[1] Spitzig et al.[1] showed that the strength of heavily cold-worked Cu-Nb microcomposite wires increased as the spacing between filaments decreased. The particularly attractive feature of these microcomposites is the combination of high strength plus high electrical and thermal conductivity.[1–7] Since the solid solubility of alloying element in Cu matrix for these microcomposites is quite small, the conductivity of the copper is not substantially reduced by the addition of alloying elements. It has been demonstrated that the similar mechanical properties were observed in other deformation processed microcomposites such as Cu-Cr, CuTa, and Cu-Fe.[8,9] The Cu-Fe system is of particular interest because of the relatively low cost of iron compared to the other possible insoluble bcc phase. However, the relatively high solubility of iron in copper at high temperatures in the Cu-Fe system, coupled with the slow kinetics of iron precipitation at low temperatures,[10,11,12] is known to reduce the electrical conductivity. For this reason, studies aimed at optimizing strength and conductivity have employed thermal/mechanical treatments.[11] Previous studies have been mostly directly to binary Cu-Fe microcomposites containing over 15 vol. S.I. HONG, Associate Professor, is with the Department of Metallurgical Engineering, Chungnam National University, Taejon 305-764, Korea. J.S. SONG, formerly Graduate Student, Department of Metallurgical Engineering, Chungnam National University, is Postdoctoral Research Fellow, Korea Atomic Energy Research Institute. Manuscript submitted January 31, 2000. METALLURGICAL AND MATERIALS TRANSACTIONS A
pct Fe.[2,9–12] With the reduction of Fe content, the conductivity is expected to increase at the expense of the strength, which could result in Cu-Fe microcomposites with favorable mechanical and electrical properties. In this study, the structure-property relationship in thermomechanically processed Cu-Fe based microcomposites alloyed with the third alloying elements such as Ag and Cr was examined. The primary purpose of this study is to investigate the effect of the third alloying elements on the microstructure and physical properties of deformation processed Cu-Fe-X microcomposite wires. II. EXPERIMENTAL PROCEDURE Billets of Cu-9 wt pct Fe-1.2 wt pct X, with X being Ag or Cr, were prepared by induction melting in air. Cylindrical billets were about 60 mm in diameter and about 112 mm in length. Extrusion of cylindrical billets was carried out at 500 ⬚C, reducing the billets from 60 to 24 mm diameter. The extruded rods were then rod rolled to 6 m
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