Deformation-induced homogenization of the multi-phase senary high-entropy alloy MoNbTaTiVZr processed by high-pressure torsion

Dendritic microstructures are frequently observed in as-solidified refractory high-entropy alloys (RHEAs), and their homogenization typically requires a long-term heat treatment at extremely high temperatures. High-pressure torsion (HPT) has been shown to be capable of mixing immiscible systems at room temperature, and therefore represents a promising technique for homogenizing dendritic RHEAs. In this work, the as-solidified RHEA MoNbTaTiVZr was processed up to 40 revolutions by HPT. It was found that the dendritic microstructure was eliminated, resulting in a chemical homogeneity at a von Mises equivalent shear strain of about 400. The study of deformation mechanism showed an initial strain localization, followed by a co-deformation of the dendritic and interdendritic regions. In the co-deformation step, the Zr-rich interdendritic region gradually disappeared. The deformation-induced mixing also led to the formation of an ultra-fine grained (UFG) microstructure, exhibiting a grain size of approximately 50 nm. The microhardness increased from 500 HV in the as-solidified to 675 HV in the homogenized UFG state. The underlying mechanisms responsible for the microhardness enhancement, such as grain refinement and solid solution strengthening, were also discussed.

Automated summary

Dendritic microstructures in refractory high-entropy alloys can be homogenized by high-pressure torsion at room temperature, eliminating the need for long-term heat treatment. In this study, MoNbTaTiVZr alloy was processed by high-pressure torsion, resulting in the elimination of dendritic microstructure and the formation of a chemically homogeneous ultra-fine grained (UFG) microstructure. The microhardness of the alloy increased from 500 HV to 675 HV in the homogenized UFG state. The mechanisms responsible for the microhardness enhancement, including grain refinement and solid solution strengthening, were discussed.