Phase transition and mechanical performance evolution in TiVZr-Nbx alloys

Abstract

The use of high-performance, lightweight advanced materials in aerospace equipment construction can reduce weight while improving service performance. Therefore, developing high-performance and lightweight structural materials with high strength and high structural stability is crucial for the aerospace industry’s technological advancements. In this study, the crystal structure, microstructure, and mechanical performance evolution of TiVZr–Nbx alloys (x = 0, 10, 15, 20, and 25 at%) were analyzed to investigate the transformation from an equimolar ternary alloy to a quaternary alloy. The density of the alloys increased from 5.8 to 6.5 g/cm3 when the crystal structure changed from the complex phases of the body-centered cubic (BCC) solid solution plus V-rich and Zr-rich phases to the BCC-dominated phase (98 %). The atomic radius differenceδ for forming such a BCC-dominated phase must satisfyδ≤6.1%. The TiVZr–Nbx(x = 0, 10, 15 at%) alloys comprised coarse grains with lots of inclusions at the grain boundaries or inside the grains. The inclusions are eutectoid agglomerate of BCC-V(s) and HCP-Zr(s), which improved the room-temperature tensile strength while decreasing plasticity. Tensile strength increased with increasing Nb content at high temperatures, and the equimolar TiVZrNb alloy exhibited the highest resistance to softening, although its strength rapidly decreased below 150 MPa at 800 °C. We observed precipitates of the hcp-Zr phase beginning at approximately 400 °C when the high-temperature thermal stability of the TiVZrNb alloy was investigated. This caused less disorder in the multi-principal solid solution and weakening of the atomic bonding force, resulting in low tensile strength at 800 °C. This study provides the foundation for understanding the high-temperature thermal stability of refractory high-entropy alloys and their failure mechanisms.