Heterogeneous deformation behavior of hybrid manufactured high strength titanium alloy: Coordinate deformation and stress concentration

Hybrid manufactured titanium alloys have a broad application prospect in aero-engine for designable mechanical properties and high benefits. However, in recent studies, titanium alloys prepared by hybrid manufacturing always broke in heat affected zone (HAZ) during tensile test. In order to further study this failure behavior and clarify the failure mechanism caused by microstructure of hybrid manufactured samples, a hybrid manufactured Ti–5Al–2Sn–2Zr–4Mo–4Cr sample was fabricated by wrought and laser directed energy disposition technology in this experiment. Microstructure formation mechanism of the hybrid manufactured sample was analyzed, and the tensile behavior was observed from both macro and micro perspectives by digital image correlation (DIC) measurement and in-situ tensile test. Sample can be divided into four zones according to microstructure characteristics, respectively additive manufacturing zone (AMZ), initially deposited zone (IDZ), heat affected zone (HAZ), and wrought zone (WZ). Microhardness of HAZ is the lowest because primary α phases coarsened and secondary α phases dissolved under cyclic heat effects during the deposition process. Because of the large temperature gradient at early deposition, IDZ has fine α phases and the highest microhardness. The heterogeneous deformation behavior observed macroscopically by DIC shows the stress concentration first occurs in HAZ. In-situ tensile test shows that coordinated deformation among grains and stress concentration at α/β phase interfaces are key factors of crack initiation and failure. The interaction forces between grains with different deformability are caused by coordinated deformation. The α phases favorable to deformation rotate towards tensile axis, while stress concentration occurs at phase interfaces of α phases unfavorable to deformation and then produces micro holes.