Investigation on hot deformation behavior of nanoscale TiC-strengthened Cu alloys fabricated by mechanical milling

In this work, ultrafine-grained (UFG) copper alloys dispersed with nanoscale TiC particles were produced by combination of mechanical milling and spark plasma sintering (SPS). Microstructure evolution during uniaxial compression to height reduction of 20-60% in the temperature range of 400-700 °C was investigated systematically. The stress-strain curves in all conditions were characterized by a fast increase in stress at initial stage and a subsequent yield drop. No obvious microstructure change was observed with increasing reduction ratio. There exhibited a tendency in grain size refinement with increasing strain rate even the change in grain size is slight. A slight grain growth was found with the compression temperature high up to 700 °C. The high temperature tensile tests results suggested that the yield stress showed a relatively weak dependence on strain rate with a strain rate sensitivity parameter of around 0.02, and a low degree of strain hardening was observed. In addition, the recrystallization behavior was found to be inhibited by the ultrafine grains and nanoscale TiC particles in starting microstructure, because the grain boundaries or junctions in initial structure act as the severe pinning points, limiting bowing, and the nanoscale TiC particles prevent the nuclei formation of recrystallization. The fracture morphologies occurred during the tensile test were closely related to the change in particles distribution from random to aligned distribution during the hot press deformation.