Effects of tungsten addition on the microstructural stability and properties of Ti-6.5Al-2Sn-4Hf-2Nb-based high temperature titanium alloys

The microstructural evolution, oxidation resistance and mechanical properties of Ti-6.5Al-2Sn-4Hf-2Nb-based alloys with different contents of tungsten (W) additions ranging from 0 to 4.0 wt.% have been investigated in this study. The addition of W changed the microstructure from Widmanstätten colony of the W-free alloy to basketweave microstructure. After thermal exposure at 650 °C for 1000 h, the retained β phase became less continuous, and secondary β nano-particles with high W concentration were precipitated from α lamellas. Within α lamellas, the W was found to mainly partitioned into the secondary β phase and refined the ordered α₂-Ti₃Al precipitates due to increased solubility of Nb in α₂ phase. High W addition increased activation energy for oxidation, promoting the formation of more uniform and compact compound oxides, therefore substantially enhanced the oxidation resistance of the alloy. Besides, the W addition also improved the room and high-temperature yield strength without obviously losing plasticity after long-time thermal exposure. The improved mechanical performance was mainly attributed to the introduction of more α/β interfaces, the precipitation of secondary β phase and the refined α₂ phase with Nb segregation.