FLOW SOFTENING DURING HOT COMPRESSION OF Cu-3.45 wt.% Ti ALLOY

Abstract

Hot compression tests were performed on supersaturated Cu-3.46 wt.% Ti alloy at the temperatures of 873 K and 973 K. Constant true strain rates of 1.4 × 10 −4 s −1 and 6.9 × 10 −3 s −1 were used. The flow curves were characterized by a single peak followed by continuous flow softening until the sample fracture. The strain to the flow stress peak was found to depend on both the deformation temperature and the applied strain rate. The flow softening (flow stress decrease) was more pronounced during deformation at 873 K for the used strain rates. Strain hardening and precipitation process were together responsible for the initial hardening of the material until the flow stress maximum has been reached. Moreover, the strain localization in a form of coarse slip and shear bands was intensified with increased strain value. It resulted in additional sites for discontinuous precipitation beside the high angle grain boundaries and might be responsible for the flow stress decrease at larger strains. The microstructure of hot deformed samples did not reveal any evidence for dynamic recrystallization during hot deformation in the presence of precipitates. However, dynamic particles coarsening within shear bands was observed and has been assumed to be responsible for further strain softening of the hot deformed sample. It was also suggested that the flow stress was partly reduced due to dynamic recovery which intensified in the course of discontinuous growth and particles coarsening within shear bands. As expected, the flow stress value was affected by the discontinuous precipitation process more effectively in those samples which were deformed at higher temperatures and low strain rates. Flow localization was significantly reduced during hot deformation of the material containing the structure transformed by discontinuous precipitation. © Acta Metallurgica Inc.