Controlling the Microstructure and Properties of Ti-6.5al-2zr-1mo-1v Components Fabricated by High-Deposition-Rate Wire Arc Additive Manufacturing

Wire arc additive manufacturing (WAAM) is an economical approach to produce large titanium components with high deposition rate. However, heterogeneous microstructure and anisotropic mechanical properties are generally encountered with the titanium components deposited by high-deposition-rate WAAM. Here, hot wire process is used to improve the deposition rate and promote the columnar to equiaxed transition of WAAM titanium components. Trace boron addition is used to modify the microstructure and improve the mechanical properties of the components. The microstructure and property relationships of the components deposited by different deposition rate and composition are discussed. The use of hot wire process raises two times in deposition rate, and reduces the linear energy heat input by 39%. High deposition rate is associated with high heat input and slow cooling rate. This induces the formation of the heterogenous microstructure, which is featured by large α colonies and coarse continuous grain boundary α layer. Heterogenous microstructure results in poor and anisotropic tensile properties. With trace boron addition, the β grain size is reduced by an order of magnitude, and the formation of heterogenous microstructure is inhibited. As a result, the mechanical anisotropy is almost eliminated with a slight improvement of the tensile strength.