Effects of Annealing Temperature on the Microstructure and Mechanical Properties of the As-Cast Dual-Phased CoCuFeMnNi High Entropy Alloys Fabricated by Vacuum Induction Melting Method

This research aims to investigate the impact of heat treatment temperatures on the microstructure, hardness, and tensile properties of a CoCuFeMnNi double-phase high entropy alloy (HEA) produced using the vacuum induction melting (VIM) method. The heat treatment temperatures selected (566, 891, and 1064 °C) were determined through differential scanning calorimetry (DSC) analysis. The microstructure, structural, and mechanical properties of the heat-treated samples were analyzed using in situ x-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), hardness, microhardness, and tensile tests. Evaluation of the microstructure revealed the presence of a-Cu-rich and Cu-lean phases in the as-cast sample. Heat treatment resulted in a change in phase content, with the Cu-rich content decreasing with increasing heat treatment temperature. DSC and in situ XRD analyses confirmed recovery and recrystallization phenomena occurring at temperatures exceeding 891 °C. Mechanical tests showed that higher heat treatment temperatures led to a slight decrease in tensile strength but significantly improved failure strain in the as-cast HEA. For instance, the failure strain of as-cast samples after heat treatment at 891 °C showed an 84.2% improvement, while the tensile strength only decreased by approximately 5.28%. Additionally, an increase in heat treatment temperature changed the fracture behavior of the as-cast HEA from brittle to ductile.