Combined effect of α precipitates size and α precipitate-free zones on tensile properties in TB9 titanium alloy

In TB9 (Ti-3Al-8V-6Cr-4Mo-4Zr) titanium alloy, the studies of microstructure evolution and tensile properties in different heat treatments were investigated. Results showed that specimen solution treated at 800 °C for 0.5 h plus aged at 500 °C for 8 h, had numerous α precipitates with inhomogeneous size and distribution, characterized by α precipitate-free zones (PFZs) (No. 1 alloy). When the solution temperature increased from 800 to 810 °C, the subsequent aging at 520 °C for 8 h promoted α precipitation without PFZs (No. 4 alloy). Although PFZs are susceptible to plastic damage, the tensile strength of No. 1 alloy is higher than that of No. 4 alloy without PFZs. These phenomena will be discussed based on the viewpoint of heat treatment effect on microstructure evolution involving precipitation nucleation and growth.