The microstructure evolution and deformation mechanism of A₂/B₂ coherent refractory high entropy alloys by low-cost laser in-situ alloying

Among the refractory high-entropy alloys (RHEAs), the Al-containing RHEAs with the coherent A₂/B₂ microstructure exhibit terrible room-temperature ductility due to the continuous B₂ matrix and the Al-Zr precipitates along grain boundaries (GBs). The present study utilizes mixed powders that have fabricated A₂/B₂ RHEA with no defects, uniform microstructure, dispersed nanoscale ellipsoidal B₂ domains, and smooth GBs by optimizing process parameters and leveraging the intrinsic thermal-cycling of additive manufacturing without expensive Ru element or post-treatments. The alloy's large tensile plasticity is attributed to the diffusion of secondary microbands that effectively address the strain localization caused by the “softening of the slip plane” of primary microbands, and high yield strength is primarily related to solid solution strengthening and B₂ strengthening. This work represents a valuable attempt to prepare defect-free, low-cost, and homogeneous A₂/B₂ RHEAs using laser in-situ alloying technology and provides valuable insights into the deformation behavior of coherent A₂/B₂ alloys.