Effect of Zr/Ta Ratio on Microstructure and Mechanical Properties of Zr-Ti-Nb-Ta Refractory High-Entropy Alloys

Abstract:

Optimal combination of strength and ductility for refractory high-entropy alloys (RHEAs) can be achieved by regulating the alloy composition that induces the mismatch between atomic size and modulus. Thus, the influence of Zr and Ta on the microstructure evolution and room-temperature mechanical properties of Zr_45-xTi₁₅Nb₃₀Ta_10+x (x=0, 5, and 10, at %) RHEAs was investigated. Results show that the variation in the Zr/Ta ratio does not change the phase composition of the alloys. All three alloys are only composed of body-centered cubic phase. However, with the decrease in Zr/Ta ratio, the yield strength and ductility of the alloys are increased simultaneously: the yield strength increases from 901 MPa to 1003 MPa, and the elongation increases from 13.3% to 16.1%. The enhancement in ductility is primarily caused by grain refinement and the decrease in lattice distortion. Meanwhile, the increase in yield strength is mainly attributed to the synergistic effect of the increased shear modulus mismatch induced by the higher Ta content and the grain refinement strengthening. This study provides valuable insights into the influence of composition variation on the properties of RHEAs.