Microstructure and Mechanical Properties of an Ultrahigh-strength Titanium alloy Ti-4.5Al-5Mo-5V-6Cr-1Nb Prepared Using Laser Directed Energy Deposition and Forging: A Comparative Study

Abstract

The application of titanium alloys in aerospace put forward the requirement for higher strength. Additive manufacturing is a promising method for the efficient and economical processing of titanium alloys. However, research on the additive manufacturing of ultrahigh-strength titanium alloys is still limited. The mechanisms of microsegregation for high alloying elements and poor plasticity are still not clear. In this study, an ultrahigh-strength titanium alloy Ti–4.5Al–5Mo–5V–6Cr–1Nb (TB18) was prepared using two methods: laser direct energy deposition (LDED) and forging. The LDEDed alloy contains three zones with similar grain morphologies but different microstructure. The microsegregation of the alloy is limited due to the rapid solidification and almost eliminated after the thermal cycle and solution treatment. With stress relief treatment, the LDEDed alloy exhibits anisotropic mechanical properties. After solution and aging treatments, its ultimate strength is enhanced; however, its plasticity is relatively lower than that of the wrought alloy with equally high strength. The excellent balance of the strength and plasticity of the wrought alloy can be ascribed to the formation of α_WGB and multiscale α laths, which provides enlightenment for optimizing the properties of the LDEDed alloy.