Effects of equal channel angular pressing processing routes on the microstructural evolution and mechanical properties of Cu–Ni–Cr alloy

Abstract

The dendritic microstructure of Cu–Ni–Cr alloys is typically associated with low formability. Previous studies have demonstrated that equal channel angular pressing (ECAP) can refine the microstructure and enhance mechanical properties. However, when only a single ECAP pass is applied, uniform microstructural evolution and hardness distribution cannot be fully achieved. In this study, the effects of different ECAP processing routes on microstructural evolution and hardness were systematically investigated. The following three secondary ECAP routes were considered: (i) 90° rotation along the longitudinal axis (2P-L90), (ii) 180° rotation along the longitudinal axis (2P-L180), and (iii) 180° rotation along the transverse axis (2P-T180). Microstructural evolutions were observed for all planes, and the microhardness at three positions on each plane was measured. After the second ECAP pass, uniformity in both microstructural evolution and hardness was achieved through the 2P-L180 processing route. A uniform hardness of approximately 287 HV was obtained, representing increases of approximately 64.87% and 5.93% compared with the initial and single-pass ECAP specimens, respectively. The secondary dendrite arm spacing and hardness further evidenced the influence of ECAP processing routes on the deformation of dendritic microstructures in each plane, in contrast to the behavior of non-dendritic materials, particularly in planes subjected to tensile loading. Specifically, hardness improvements were achieved mainly under compressive loading. Therefore, achieving hardness uniformity across all planes remained difficult with the ECAP processing routes suggested in earlier studies. The findings of this study support the adoption of 2P-L180 processing route for Cu–Ni–Cr alloys as a guideline for improving both hardness and its uniformity in materials with dendritic microstructures.