  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.
