Isolating the influence of residual stress on tensile behaviour of laser-based powder bed fusion Ti alloys via mechanical stress relief

This study proposes a mechanical stress relief (MSR) process to reduce the residual stress in PBF-LB materials. It involves progressive, slow cyclic loading in the material's elastic region. Two Ti alloys, Ti-6Al-4V and Ti-7Cr-4Sn, were chosen as model alloys and underwent MSR accordingly. Results suggest that the proposed MSR helps reduce residual stress, and its effectiveness in relieving residual stress is similar across the two alloys. However, the influence of MSR on the tensile performance is different in the two alloys, which is affected by the initial residual stress level and the material's deformation mechanism. Ti-6Al-4V possesses high residual stress, with deformation slip being the only deformation mechanism. In contrast, Ti-7Cr-4Sn possesses relatively low residual stress, and a unique deformation mechanism involves {332}<113> twinning and ωiso precipitates. Such a unique deformation mechanism leads to crack initiation driven by twin-confined dislocation pile-up.