Microstructural evolution and mechanical property of high-strength metastable β titanium alloy joint via electron beam welding

Obtaining a fundamental understand of the relationship between weld microstructure and mechanical properties is critical for ensuring a high weld quality. This work explored the micro-mechanism responsible for the mechanical properties of a 10-mm-thickness metastable β titanium alloy (Ti–3Al–5Mo–4Cr–2Zr–1Fe, wt.%) joint welded by electron beam welding (EBW). Weld microstructure and its evolution behavior were revealed by means of multi-scale microstructure characterization. Obtained results indicate that the absence of α phase and formation of nano-scale ω particles occurred in the coarse columnar β grains of the fusion zone (FZ). Intense dissolution and significant coarsening of secondary α phase occurred in the heat affected zone. Between the FZ and HAZ, a partially melted zone was observed and contains few equiaxed β grains. Compared to the base material, the as-welded EBW joint shows significant softening in weld seam and a slight decrease of 17% in ultimate tensile strength, while a severe reduction of 73% in elongation. It was observed that majority of plastic deformation is confined to the narrow FZ, indicating a significant localization of tensile strain. This leads to premature fracture of the joint within the FZ and consequently to significant deterioration of the overall ductility. This work contributes to advancing the understanding of the role of microstructural evolution on the mechanical properties of high-strength titanium alloy joints via EBW.