Grain boundary sliding with diffusional accommodation enable dynamic recrystallization during hot deformation of coarse-grained body-centered cubic HfNbTaTiZr high-entropy alloys

The origin of ultrafine grain refinement durig hot deformation of equiatomic HfNbTaTiZr body-centered cubic (BCC) high-entropy alloy (HEA), having an initial grain size, d ∼ 140 μm is systematically investigated. Microstructural observation at very low strain (ε ∼ 0.04) interval showed unique saw-toothed and stair case-like ledges along the initial grain boundaries (GB). Further analyses showed triple junction folds, and shear offsets at the scratch line and GB intersections suggesting a grain boundary sliding (GBS) mechanism. This study shows direct evidence for the possibility of GBS mechanism in a coarse grained HfNbTaTiZr BCC-HEA, for the first time. The possibility of ultrafine grain refinement is discussed using GBS mechanism with diffusional accommodation. The present study featuring coarse grained GBS mechanism in HfNbTaTiZr alloy provided insights into the high energy GB structure of refractory BCC-HEAs.