Deformation processing and mechanical properties of Cu–Cr–X (X=Ag or Co) microcomposites

Abstract

The strength of Cu–Cr–X (X=Ag or Co) improved by intermediate heat treatments during the rolling process. The strength (798 MPa) of Cu–Cr–Ag microcomposites with intermediate heat treatments at 550 °C (IH 550) was found to be better than that of Cu–Cr–Ag microcomposites (423 MPa) with no intermediate heat treatment (NH). The improvement of the strength is attributed to the refinement of the microstructural scale by thermo-mechanical processing involving intermediate heat treatments. Severely elongated Cr filaments along with relatively coarse elongated Cr particles are clearly observed on the longitudinal sections. The Cr particles in Cu–Cr–Ag microcomposites were observed to be larger than that of Cu–Cr–Co microcomposites because of the initially coarser Cr dendrites. On the other hand, the width between filaments in Cu–Cr–Ag (2.4 μm) was found to be slightly smaller than that of Cu–Cr–Co (2.44 μm). The finer filamentary structure in Cu–Cr–Ag can be attributed to easier refinements due to the stronger Cu matrix strengthened by Ag precipitates. Cu–Cr–Ag and Cu–Cr–Co microcomposite plates exhibited ductile fractures. The surfaces of the microcomposite plates show many fine dimples and relatively coarse dimples. Examination of the coarse dimples on the fracture surfaces revealed fractured Cr filaments or particles in the center.