Achieving superior performance in powder-metallurgy near-β titanium alloy by combining hot rolling and rapid heat treatment followed by aging

Heat treatment plays an important role in tailoring the mechanical properties of powder-metallurgy (PM) titanium alloys. However, only limited work about the rapid heat treatment (RHT) of PM titanium alloys has been reported. In this work, RHT was applied to PM Ti–5Al–5Mo–5V–1Cr–1Fe alloy after hot rolling to study the evolution of its mechanical properties and the influence of residual pores on its properties. Through hot rolling and annealing, a fine and uniform α + β structure with few residual pores is obtained. During RHT, the primary α dissolves gradually and completes in the β region, and the β grains then grow, resulting in the continuous decrease in elongation after aging. Moreover, the tensile strength first increases and then decreases with increasing RHT temperature, owing to the increase in volume fraction of secondary α in α + β region and the β grain growth in β region. In contrast to the RHT of cast-and-wrought titanium, the negative influence of residual pores lowers the RHT temperature for obtaining the highest tensile strength to a temperature below the β-transus temperature. Despite the negative influence of the residual pores, retained primary α and fine β grains with fine secondary α inside contribute to achieving a good strength/ductility balance (1570 MPa and 6.1%, respectively). Additionally, although at higher cycles to failure, the negative influence of residual pores increases as it affects the crack initiation zone at the subsurface, the good resistance of secondary α to fatigue crack propagation still enhances the fatigue strength considerably (about 300 MPa). This work suggests a cost-effective strategy to produce titanium alloys with high performance.