Effect of homogenization annealing on microstructure and mechanical properties of AlMo0.5NbTa0.5TiZr refractory high entropy alloy manufactured by laser metal deposition

The AlMo_0.5NbTa_0.5TiZr refractory high-entropy alloy (RHEA) has garnered significant attention for its excellent high-temperature properties and low density, indicating substantial potential in aerospace applications. Laser powder deposition (LMD) is an ideal method for fabricating RHEAs due to its rapid cooling and minimal secondary processing. The effects of homogenization annealing on the microstructure and mechanical properties of AlMo_0.5NbTa_0.5TiZr RHEAs fabricated by LMD are reported for the first time. The LMD alloy consists of columnar dendrites, with dendritic regions enriched in Mo, Nb, and Ta, and interdendritic regions enriched in Al, Zr, and Ti. Additionally, an AlZr HCP phase is observed. After annealing at 900 °C and 1100 °C, the dendritic structure persists. Zr first precipitates in the interdendritic regions, combining with Al to form the AlZr HCP phase. At 1300 °C for 10 h, complete homogenization is achieved, forming a nano-scale basket-weave structure within the equiaxed grains, and reaching the maximum yield strength of 2289 MPa. As the annealing time increases, the basket-weave structure coarsens, resulting in a decrease in microhardness (from 640 HV to 603 HV) and compressive strain (from 11.92 % to 10.48 %). The non-sluggish diffusion behavior of Zr in AlMo_0.5NbTa_0.5TiZr RHEAs primarily drives the microstructural evolution and the formation of multiphase structures. This study adjusts the morphology of the precipitates through heat treatment to achieve excellent mechanical properties, providing a reference for the development of heat treatment regimes.