Eliminating continuous grain boundary α phase in laser melting deposited near β titanium alloys by heat treatment

Abstract

Continuous grain boundary α phase (αgb) is widely present in laser melting deposited near β and β titanium alloys, and it can lead to intergranular fracture and low ductility. Because of the preferential nucleation and growth of α phase at β grain boundaries, the continuous αgb cannot be effectively eliminated by traditional heat treatment. Thus, in this study, we develop a new heat treatment including beta solution + ultra-slow furnace heating up + traditional heat treatment, to eliminate continuous αgb in laser melting deposited Ti-5Al-5Mo-5V-1Cr-1Fe near β titanium alloy, and the microstructures and tensile properties are investigated. The results indicated that, after beta solution + normal heating up + traditional heat treatment, the continuous αgb still exists, and the elongation is still low about 7.5%. However, after beta solution + ultra-slow heating up + traditional heat treatment, there are almost no continuous αgb, and the elongation increases to 15.2%. The mechanism about the αgb formation during ultra-slow heating up process is simply revealed. Furthermore, this new heat treatment is also suitable to eliminate continuous αgb for laser melting deposited Ti17 alloy.