Simultaneously achieving exceptional and heat treatment insensitive strength-ductility synergy in an α+β titanium alloy via tailoring silicide and heterogeneous α precipitates

The development of cost-effective titanium alloys with outstanding mechanical properties has always been a primary concern of the modern aerospace industry. However, the intrinsic sensitivity of their α precipitates to heat treatments proliferates the manufacturing costs to achieve desirable strength and ductility, especially in engineering occasions. In current work, a silicide-containing α+β Ti-5Al-7.5V-0.5Mo-0.5Zr-0.5Si (TC5751S) alloy has been evidenced to exhibit advanced mechanical properties with reduced sensitivity to heat treatments. It is noted that more nano-scale secondary α (α_s) precipitate with a simultaneous dissolution in micron-scale primary α (α_p) and (Ti, Zr)₅Si₃ silicides in the current alloy as the solution temperature increases. However, this alloy shows excellent and stabilized strength-ductility synergy in all cases (ultimate tensile strength: 1335±30 MPa, yield strength: 1245±30 MPa, fracture strain: 9.6 %±0.5 %) irrespective of the aforementioned variations in the microstructure. This stabilized strength and ductility of TC5751S are rationalized based on the compensation mechanisms between the contributions from silicide and heterogeneous α precipitates. The quantitative analysis unveils that the increased α_s/β phase boundary strengthening (σ_PB) is approximately offset by the decrease in silicide strengthening (σ_silicide) due to silicide dissolution with increasing solution temperatures, leading to the strength of TC5751S in a dynamic equilibrium state. Simultaneously, the dissolution of silicides reduces the cracking tendency and complements the ductility loss due to α_p reduction and α_s precipitation, leading to the ductility insensitive to heat treatments. Therefore, the compensating role of silicides to the effects of heterogeneous α precipitates on both the strength and ductility of titanium alloys has been well-verified in our work, providing a novel pathway to the development of high-performance titanium alloys friendly to processing strategies.