Formation and evolution of precipitates in an additively manufactured near-α titanium base alloy

Abstract

Titanium base alloys are frequently used in laser powder bed fusion manufacturing processes and enable the production of lightweight and complex components. This study describes the influence of the heat input and various post-process heat treatments on the martensite formation and its decomposition in an additively manufactured Ti-6Al-2Sn-4Zr-2Mo-Si alloy. The change of the martensite crystal structure from orthorhombic to hexagonal, caused by additional heat input, was proven by high-energy X-ray diffraction. It is shown that the heat input of the laser affects the diffusion of alloying elements such as Mo and Si. This behavior was investigated by atom probe tomography, which confirms clustering of Mo and Si at dislocations and grain boundaries, and allows for linking the heat input during the manufacturing process with the morphology of the observed clusters. Moreover, particular emphasis is laid on explaining the formation mechanism of (Ti,Zr)6Si3 silicide particles during a subsequent heat treatment.