Microstructure and mechanical properties evolution of near-β alloy Ti-4Al-6Cr-5Mo-5Nb-xTa

To meet the aerospace industry’s demand for aircraft featuring high thrust-to-weight ratios and lightweight structures capable of operating in complex service environments, β titanium alloys with high specific strength and good plasticity have become a current research hotspot in the development of domestic fasteners. Based on the calculated Mo equivalent, the alloy composition Ti-4Al-6Cr-5Mo-5Nb is classified as a near-β titanium alloy within the titanium alloy design space. The microstructure is further controlled by adding alloy element Ta with a mass fraction of 0.4wt.%−2.0wt.%. Research results indicate that Ta dissolves completely in the matrix without forming new phases within the investigated range. As the Ta content increases, the proportion of the β phase increases significantly, the β grain diameter decreases markedly from 2.4 mm to 0.4 mm, and the a phase gradually coarsens. When adding 1.6wt.% Ta, the tensile strength and fracture toughness of the alloy reach the peak values of 735 MPa and 55 MPa·m^1/2, respectively.