Effect of annealing conditions on microstructure and hardness of CoCrFeNiMn-0.18Ti high entropy alloy manufactured by electron beam melting

Abstract

The success of in situ alloying whilst developing high entropy alloys (HEAs) specific to the electron beam melting (EBM) process has been stated in the literature. Secondary phases forming on FCC matrix improved the mechanical properties of EBM-built; however, their random distribution limits the further improvement in mechanical performance. Herein, post-process heat treatments were designed to observe the effects on secondary phase morphology, distribution, and microhardness of EBM-built CoCrFeNiMn-0.18Ti HEA and establish the optimized heat treatments while reducing further cost. Systematic studies revealed that an increase in solutionizing time slightly enhanced the microhardness of the alloy despite the solutionizing temperature reversely affect the mechanical properties. On the one hand, reaching a solutionizing temperature of 1300°C would not be enough to dissolve all the secondary phases within a reasonable solutionizing time of two hours. Metastability of HEAs and the complex distribution of topologically formed secondary phases slowed down phase transformations through FCC matrix. On the other hand, the microhardness of samples was successfully reattributed at 600°C by annealing. Thirty minutes and fifteen hours of annealing improved the hardness of solutionized alloy by 58 and 150% while reaching 316 HV and 487 HV, respectively.