Effect of aging treatment on microstructure and tensile properties of Ti–4Al–6Mo–2V–5Cr–2Zr

Abstract

Microstructure of novel high-strength metastable β titanium alloy, Ti–4Al–6Mo–2V–5Cr–2Zr, is extremely sensitive to both aging temperature and time length, which directly regulates their mechanical properties. Therefore, it is particularly important to clarify the roles of aging treatment in both microstructure and mechanical properties of Ti–4Al–6Mo–2V–5Cr–2Zr. Through varying the aging temperature from 520 to 640 °C and time from 2 h to 8 h, effects of aging technological parameters on the microstructure and tensile properties of Ti–4Al–6Mo–2V–5Cr–2Zr was systematically investigated. It is noted that the secondary α phase (αs) inside the β matrix coarsens as a function of the aging temperature and time length, and the shape of αs phase changes from fine needle to short rod. Moreover, lower aging temperature and longer aging time result in a higher volume fraction of αs phase. Combined with tensile test results, it is evident that volume fraction of αs phase leads to high strength. The volume fraction of αs phase in the alloy after aging at 520 °C for 6 h reaches 61.9% along with the highest ultimate tensile strength of 1367 MPa. In addition, the strengthening mechanism of reinforced phase αs was clarified with both SEM and TEM observations. Results show that the αs with the internal lattice distortion and HCP structure effectively prevent the dislocation slip. And the αs phase arranged in a triangular shape has a profound strengthening effect.