Effect of Heat Treatment on Toughness Improvement and Microstructure of Co35Cr10Ni43Ti12 Medium-Entropy Alloy Fabricated by Powder Plasma Arc Additive Manufacturing

In this study, the effects of heat treatment at 1000℃ and 1100℃ on the microstructure and mechanical properties of Co35Cr10Ni43Ti12 medium-entropy alloy (MEA) were investigated, a novel MEA Co35Cr10Ni43Ti12 was fabricated by the technique of powder plasma arc additive manufacturing. The effects of the evolution of microstructure on the mechanical properties were analyzed by XRD, SEM and EBSD. Co35Cr10Ni43Ti12 MEA showed a dual-phase structure of FCC and η, and the FCC grains exhibited a typical <001> columnar crystal structure along the build direction. After heat treatment at 1000°C, the η phase was transformed from blocky to plate-like with granular, and after heat treatment at 1100°C, all of the η phase in the alloy was transformed into plate-like. For the plate-like η phase, there were 111FCC∥{0001}η and 011FCC∥[21̅1̅0]η orientation relationships with FCC, which were typical N-W orientation relationships. The printed alloy exhibited high tensile strength of 1214MPa and low elongation of 2.8%, and after heat treatment at 1000 °C and 1100 °C, the tensile strength of the alloys decreased to 882MPa and 807MPa, respectively, and the elongation increased to 10.6% and 15.4%.