Mechanical properties and microstructural evolution of near α titanium alloy TA15 manufactured via laser powder bed fusion before and after heat treatment

In this work, the influence of annealing temperatures (650℃–950℃) on the microstructure and mechanical properties of TA15 (Ti-6Al-2Zr-1Mo-1V) titanium alloy, fabricated via laser powder bed fusion (L-PBF), is investigated. A hierarchical microstructure with an acicular α′ martensite structure is developed in the as-printed TA15 alloy, due to the rapid cooling associated with the L-PBF process. The decomposition of α′ martensite into the α+ β phase occurs during annealing treatment, and the size of both the α and β phases increases with increasing annealing temperature. The fine α′ needles show strong resistance to dislocation activity, leading to a high strength (>1200 MPa) but low ductility (<6 %) of the as-printed alloy. With the increase of annealing temperatures, the strength of the TA15 alloy gradually decreases, while the ductility increases, providing a feasible approach to obtain a desired combination of strength and ductility. The 950℃ annealed samples show a high elongation of > 10 %, while retaining a strength above 850 MPa. All the samples show weak anisotropy in mechanical properties, mainly due to the fact that the mechanical properties are determined by the hierarchical α′ or α microstructure.