Internal tensile properties of characteristic zones in the electron beam weldment of TC17 titanium alloy

Abstract

The internal tensile deformation of the individual base metal zone (BM), heat-affected zone (HAZ), and fusion zone (FZ) in a titanium alloy (Ti–5Al–2Sn–2r–4Mo–4Cr, wt.%) electron beam welding (EBW) joint is investigated. The ultimate strength of BM with a bimodal microstructure is 1047.5 MPa, and the elongation to fracture is 9.8%. HAZ is distinguished by the formation of a ghost structure with a hierarchical cluster structure within the initial αP grains, while the embedded αs laths dissolve in the matrix and relatively coarsening β grains are generated. During tension, the ghost structures strongly inhibit and deflect slip initiation and extension in the relatively coarsening β matrix. The competitive balance between strengthening from the ghost structure and weakening from the coarsening matrix dominates the mechanical properties of the HAZ, which then induces a hybrid fracture. The needle-shaped thermal martensite that formed during EBW causes the FZ to fail prematurely. The microstructural evolution of HAZ and FZ decreases their mechanical properties. This research may shed some light on the mechanical enhancement of titanium alloys by utilizing the multiple αL laths precipitated within the initial αP structure associated with the bimodal matrix.