Effect of solution and aging on phase stability and mechanical properties of Zr–Ti–Nb–Ta refractory medium entropy alloy

Abstract

Refractory high/medium-entropy alloys (RHEAs/RMEAs) are promising structural materials for high-temperature applications due to their unique composition and outstanding properties. However, phase stability at intermediate temperatures (773–1173 K), as well as the mechanical behavior of this class of RMEAs (Zr45Ti15Nb20Ta20, at %), needs to be better understood to make the alloys applicable to industry. Therefore, we took the alloy as a model and investigated in detail the phase transformation and the effect on mechanical properties under different heat treatment processes. When aged at 773 K, Zr45Ti15Nb20Ta20 RMEA experienced spinodal decomposition to form a high-density nanocubic structure. Spinodal decomposition strengthens the RMEA, achieving a room temperature hardness of 528 HV and a compressive yield strength of 1608 MPa, also has 63.8% higher high-temperature strength than cast RMEA. The Nb–Ta-rich BCC2 phase is distributed as particles within the grain and as continuous rods at the grain boundaries, after aging at 973 and 1173 K. Accumulation of dislocations at second-phase particles reduces the dynamic recovery (DRV), allowing a discontinuous dynamic recrystallization (DDRX) mechanism to dominate the dynamic recrystallization (DRX) during the high-temperature deformation process. Ultra-fine DRX grains and their random weaving support the occurrence of grain boundary slip (GBS) during high-temperature deformations. These results indicate that the mechanical properties of RHEAs/RMEAs can be fully optimized by regulating the microstructure through effective heat treatment processes, providing novel insights for the design of high-performance RHEAs/RMEAs.

Keywords

• Refractory medium entropy alloy
• Phase decomposition
• Microstructure
• Mechanical properties
• Dynamic recrystallization