Influence of tantalum composition on mechanical behavior and deformation mechanisms of TiZrHfTax high entropy alloys

The effects of metastability engineering on tuning deformation behavior and deformation mechanisms in TiZrHfTaX (x = 1.00, 0.80, 0.60, 0.50) refractory body-centered cubic (BCC) high entropy alloys were investigated, with specific emphasis on elucidating the underlying interplay between phase stability, mechanical property, and deformation twins. It was found that in proper thermomechanical treated samples, a variation of tantalum content can effectively tune the activation of various deformation mechanisms. Detailed electron back-scattered diffraction and transmission electron microscopy analyses revealed for the first time that {332}<113̅>BCC twinning, deformation-induced α’’ phase, {111}α’’ type I and <2̅11>α’’ type II twinning can be sequentially activated in TiZrHfTaX (x = 1.00, 0.80, 0.60, 0.50) high entropy alloys with decreasing the content of tantalum. The comprehensive strengthening effect of transformation induced plasticity and twinning induced plasticity, was discussed and attributed as the pivotal factor for the improved work hardening capability and mechanical performances, especially for alloys with lower tantalum contents. Consequently, we extended the conventional bond order and d‐orbital energy level diagram that was originally developed for body-centered cubic titanium alloys for deformation mechanism evaluation to body-centered cubic high entropy alloys on the basis of current results, which sheds light on the design of ductile body-centered cubic high entropy alloys with expected deformation mechanisms and optimized mechanical performance.