Process design and microstructure-property evolution during shear spinning of Ti2AlNb-based alloy

Abstract Rotationally symmetric workpieces of Ti2AlNb-based alloys have great potential for high-temperature service condition in aviation industry, while the poor workability limits their application until now. In this study, shear spinning and heat treatment were first conducted to investigate the corresponding microstructure evolution and mechanical properties of Ti2AlNb conical workpieces. The microstructure of the 1st and 2nd pass spun workpieces (SP1 and SP2) mainly consisted of B2 + retained α2 phases. After two passes spinning, the B2 phase texture changed from //ND of as-received alloy to be //ND. The ultimate tensile stress (UTS) of SP1 and SP2 was increased to 1163 MPa and 932 MPa, respectively, compared with 782 MPa of as-received alloy at 650 °C. Also, the yield stress anomaly (YSA) occurred in SP1 and SP2 because {110} and {112} cross slip systems of B2 phase were difficult to slip at or below room temperature (RT), but they became active at 650 °C and above. As an essential step for increasing the spinnability of multi-pass spinning process of the Ti2AlNb alloy, the H3 heat treatment scheme, i.e. 960°C/2 h+ 850°C/12 h, was carried out between two successive passes to increase the hot workability, by which the ductility of the heat treated as-spun workpieces with the microstructure of B2 + primary O + acicular secondary O + high amount spheroidized α2 phases reached 72.1% at 900°C. After being subject to the H1 heat treatment scheme, i.e. 960 °C-2 h, the spun workpieces with the microstructure of B2 + primary O + intergranular primary α2 phases achieved an optimized comprehensive mechanical properties both at room temperature and 650°C, which should be chosen as the post-spinning heat treatment process for the service requirement.