Deformation kinking and stress-induced martensitic transformation in a laser-based powder bed fusion-processed metastable β Ti-5Al-5Mo-5V-3Cr alloy

The deformation mechanism in a metastable β Ti-5Al-5Mo-5V-3Cr (wt.%, Ti-5553) alloy fabricated by laser-based powder bed fusion (PBF-LB/M) was investigated using scanning electron microscopy, transmission electron microscopy, and aberration-corrected scanning transmission electron microscopy. The PBF-LB/M Ti-5553 exhibited an ultimate tensile strength of 790.2 $\pm$ 42.4 MPa and total elongation of 23.0 % $\pm$ 1.4 % at room temperature, despite notable strain softening. Unlike deformation twinning in conventionally processed Ti-5553, deformation kinking occurred in the PBF-LB/M Ti-5553 during tensile deformation and <110>_β-type kink bands formed with ∼2° to ∼11° misorientation relative to the β matrix. These kink bands accommodate local stress concentrations developed during tensile deformation, enhancing the total elongation. Additionally, nanoscale stress-induced αʺ martensite with orthorhombic structure formed at kink/matrix interfaces and within kink bands, further accommodating localized strain. The combination of deformation kinking and stress-induced martensitic transformation is believed to contribute to the excellent ductility despite strain-softening in PBF-LB/M Ti-5553.