Characteristic dislocation slip behavior in polycrystalline HfNbTiZr refractory medium entropy alloy

The present work reports characteristics of dislocation slip behavior in an equi-atomic HfNbTiZr refractory medium entropy alloy (RMEA) and its systematic comparison with pure niobium (Nb). Fully-recrystallized specimens were fabricated by cold rolling and subsequent annealing, and uniaxial tensile deformation was applied at room temperature. Slip trace morphologies on the surfaces of the tensile-deformed materials were quantitatively characterized, and the so-called ψ and χ relationships of the observed slip traces were evaluated by a newly developed method for polycrystalline specimens. Wavy slip traces were observed in most grains in the pure Nb. They consisted of low-indexed slip planes, such as {1 1 0}, and {1 1 2}, and high-indexed (or undetermined) slip planes. Some straight slip traces persisting on the low-indexed slip planes were also found in the pure Nb. In contrast, straight slip traces were dominant in the RMEA. The straight slip traces in the RMEA were not parallel to particular slip planes but mostly distributed along the maximum shear stress plane (MSSP), indicating that frequent cross slip in very short intervals occurred. Large deviations of slip planes from the MSSP in a few grains of the RMEA were attributed to the slip transfer from neighboring grains as a characteristic of polycrystalline materials. Frequent cross slip in short intervals, attributed to homogeneous slip resistance distribution for screw dislocations in the RMEA originating from the chemical heterogeneity on an atomic scale, was proposed as a novel mechanism responsible for the unique slip behavior and macroscopic deformation behavior.