Processing, microstructure, and properties of ternary high-strength Cu-Cr-Ag in situ composites

A new class of ternary in situ metal matrix composites (MMCs) with high str ength and high electrical conductivity consisting of heavily co-deformed Cu , Cr. and Ag is introduced. Three alloys are investigated in detail, namely , Cu-10wt.%Cr-3wt.%Ag, Cu-10wt.%Cr-1wt.%Ag, and Cu-4.5wt.%Cr-3wt.%Ag. The a lloys were produced by inductive melting and chill casting. Because Cu-Cr a nd Cu-Cr-AE alloys with hypereutectic Cr content are less ductile than prev iously investigated Cu-Nb, Cu-AE. and Cu-Nb-Ag alloys, special attention wa s placed on optimizing microstructure with respect to both strength and duc tility using thermal and thermo-mechanical processing schemes. These includ ed various combinations of swaging, heavy wire deformation (using different lubricants), solution annealing at different temperatures followed by quen ching, and aging at different temperatures. Optimized processing allows one to attain maximum wire strains of eta = 8.48 (eta = 1(A(0)/A), A: wire cro ss-section). The wires have very high strength (for instance Cu-10.%Cr-3wt. %Ag: 1260 MPa at a strain of eta = 8.48) and good electrical conductivity ( 62% of the conductivity of pure Cu (IACS) at a strain of eta = 2.5 after so lution treatment). Up to wire strains of eta approximate to 8.5 the strengt h is equal to that of Cu-20wt.%Nb. The wire strength is much higher than pr edicted by the linear rule of mixtures. The investigation presents the evol ution of microstructure during the various thermo-mechanical treatments and relates the results to the observed mechanical and electrical properties. The strength is discussed in terms of Hall-Petch-type hardening. (C) 2000 E lsevier Science S.A. All rights reserved.