Microstructure deformation and failure mechanism of laser direct energy deposited Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy: experimental and numerical simulation

Additive manufacturing has emerged as a highly attractive technique in fabricating large-scale and complex integral titanium alloy structures. Understanding the failure behavior of additively manufactured alloy is crucial for ensuring the structural integrity and safety of primary load-carrying components. In this study, an in-situ tensile test combined with an image-based micromechanics finite element model was employed to investigate the microstructure deformation behavior and failure mechanisms of laser direct energy deposited (LDED) titanium alloy. The LDED Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy exhibits a unique bimodal microstructure, comprising coarse lamellar primary α phase and transformed β phase matrix. During the elastic stage, the primary α phase exhibits high stresses and low strains, while the transformed β phase exhibits the opposite behavior. As the applied load increases, strain localization first occurs in the fine transformed β phase between two parallel primary α phases, leading to an earlier yield of the transformed β phase even though the alloy as a whole remains in the linear elastic regime. The yield of the majority of the transformed β phase is identified as the primary cause for the yield of tested specimen.