Effect of Ta and Ti content on high temperature elasticity of HfNbZrTa1−xTix refractory high-entropy alloys

Abstract The finite temperature elastic properties of non-equiatomic refractory high-entropy alloys (RHEAs) HfNbZrTa1−xTix are investigated using the exact muffin‑tin orbitals method in combination with coherent potential approximation and Debye-Gruneisen model, especially the effect of Ta and Ti addition is emphasized. Taking HfNbZr as a reference, the lattice constants decrease when alloying with Ta, and continue to decline slightly with replacement of Ta by Ti. Estimating from calculated elastic parameters, mere Ta addition leads to the high strength and stiffness accompanying evident lowering of ductility, while sole Ti addition brings about the high ductility at the expense of reducing strength and hardness. With substitution of Ti for Ta, HfNbZrTa1−xTix alloys achieve a relatively high ductility accompanied a gentle decline in high strength and hardness. As temperature increases, although the obtained single-elastic and polycrystalline elastic parameters exhibit decreasing trend, the anti-softening ability is enhanced with substitution of Ti for Ta, and HfNbZrTa1−xTix alloys remain an overall good combination of strength and ductility at high temperature. The proper strength-ductility trade-off can be gained by tuning Ti/Ta ratio, which is beneficial for designing the high temperature mechanical properties of alloy.