Effect of initial grain size on hot deformation behaviour of Cu-Cr-Zr-Ti alloy

Abstract

Hot uniaxial compression tests were carried out on Cu-0.8Cr-0.05Zr-0.05Ti (wt%) alloy specimens with three different grain sizes: 30 μm, 150 μm and 450 μm to study the effect of initial grain size on hot workability of the alloy. The deformation temperature and applied strain rate ranges were 600–900 °C and 0.001–1 s−1 respectively. At higher deformation temperatures, fine grained specimens exhibited early onset of dynamic recrystallization (DRX) as compared to coarse-grained specimens. Conversely, the work hardening plots of coarse-grained specimens exhibited plateaux at higher strain rates indicating occurrence of deformation twinning. Microstructure examination revealed a decrease in the extent of DRX and an increase in deformation twinning with increase in initial grain size. The failure in coarse-grained specimens was in the form of wedge cracking observed at triple junctions at lower deformation temperatures. The higher stress values exhibited by coarse-grained specimens as compared to fine grained specimens was found to be a result of absence of DRX and the strain being accommodated by deformation twinning rather than grain boundary sliding (GBS) due to limited grain boundary area. Processing maps using the dynamic material model (DMM) were plotted for all three initial grain sizes and were validated with optical microstructures. The ‘unstable/unsafe’ deformation domain was found to be wider with increase in initial grain size. The present study explicates that there is an increase in difficulty of hot working and reduced control of microstructure in the alloy with increase in initial grain size.