The effect of single-step and two-step aging on the microstructure and mechanical properties of the novel Ti-3Al-8Mo-7V-3Cr alloy

Metastable beta titanium alloys are suitable for use in the aerospace industry due to their high strength and good ductility, as well as their high strength-to-weight ratio. The aim of the current research is to investigate the microstructure and tensile properties of the alloy after single-step and two-step aging following thermal-mechanical cycles of single-phase β annealing and two-phase α+β annealing. For this purpose, on one strip of the alloy, solution annealing heat treatment in the single-phase β region, cold rolling and recrystallization and on the other strip, solution annealing heat treatment in the two-phase α+β region was performed. Afterwards, the specimens from the strips were subjected to single-step aging at 550⸰C. In addition, in order to perform two-step aging, specimens were subjected to heat treatment at 300 and 550⸰C for primary and secondary aging, respectively. Then the structural evolution of the alloy was investigated by SEM and X-ray diffraction pattern and the tensile properties of it by tensile test. It was found that the optimum heat treatment cycle of the Ti-3873 alloy was two-step aging after α+β solution treatment leading to 1190 MPa yield strength and 14.7% elongation. In this case, the obtained structure has no grain boundary alpha and the formed secondary alpha has a length of less than 0.5 µm and its average thickness is 0.15 µm.