Effect of ECAP Process and Subsequent Annealing on Microstructure and Properties of Cu-0.25Se-0.25Te Alloy

Abstract

Cu-0.25Se-0.25Te alloy has been melted in a vacuum induction furnace and then heat treated. Afterwards, equal-channel angular pressing (ECAP) and subsequent annealing were carried out on the obtained samples. The effects of the ECAP process and subsequent annealing on the microstructure and properties of the alloy have also been investigated by scanning electron microscopy, Vickers microhardness testing, and eddy-current conductivity measurements. The results suggest a morphological evolution of the grains during the ECAP process. The equiaxed grains of the heat-treated alloy initially developed into shapes elongated along the shearing plane, then a series of smaller streamlined strip-like grains appeared and were eventually crushed into fine and equiaxed grains with a size of about 5 μm after different numbers of ECAP passes (one, two, four, or eight), along with a deformed strain ε. Furthermore, the microhardness (HV) rose sharply from 68 N/mm² to 140 N/mm² and then climbed steadily to 169 N/mm² under the comprehensive effect of ε and the refinement of deformed grains. By contrast, the electrical conductivity decreased slowly from 96.2% international annealing copper standard (IACS) to 93.5% IACS. The microhardness and the electrical conductivity of the samples were found to vary contrarily with the change of annealing temperature and stabilized at 500°C. Notably, the electrical conductivity increased gradually, whereas the hardness of the alloys that were subject to a higher number of ECAP passes decreased remarkably with increasing annealing time at 300°C.