Beta heat treatment of laser melting deposited high strength near β titanium alloy

To improve the mechanical properties of laser melting deposited Ti-5Al-5Mo-5V-1Cr-1Fe high strength near β titanium alloy, the traditional heat treatment and new designed beta heat treatment are applied in this study. The corresponding microstructures and tensile properties are investigated. It is found that the traditional heat treated samples consist of continuous linear grain boundary α (α_LGB). Its formation is found to be associated with the layer by layer thermal cycling treatment in laser melting deposition process. The cracks preferentially initiate and propagate along α_LGB, leading to intercrystalline fracture and low ductility. In contrast, beta heat treatment leads to the formation of herringbone Widmanstätten grain boundary α (α_WGB). The α_WGB effectively inhibits the crack propagation along grain boundary, resulting in the predominantly transcrystalline fracture and improved ductility.