Solid-state transformations and the residual stress–texture relationship in fiber laser-welded Ti-6Al-4V

High-power fiber laser welding of Ti-6Al-4V produces a complex thermal and microstructural history, including rapid solidification, β→α′ transformations that influence both residual stress and crystallographic texture. In this study, bulk neutron diffraction, laboratory XRD, EBSD, and validated thermo-mechanical finite-element simulations were used to quantify the relationship among phase transformation, phase distribution, texture, and residual stress in 2 mm butt-welded Ti-6Al-4V sheets. The as-welded fusion zone exhibits a pronounced transformation texture inherited from columnar prior-β grains (Burgers orientation relationship), which produces strongly direction-dependent diffraction intensities. Neutron diffraction shows a tensile longitudinal core of ∼750–780 MPa at mid-thickness, balanced by mild far-field compression; transverse stresses are lower and normal stresses are negligible. Simulations that toggle the β→α′ strain demonstrate <5% change in peak stress, establishing that, unlike in steels, the small transformation strain in Ti-6Al-4V does not materially relieve weld stresses; it primarily governs texture and microstructure. A sub-transus post-weld heat treatment (600 °C, 6 h) reduces peak longitudinal stress to ∼250 MPa, approximately the alloy's yield strength at the soak temperature, while transverse/normal components collapse toward zero. Concurrently, α′ partially tempers to α+β, hardness drops by ∼10–15%, and texture intensity weakens modestly. Mechanical restraint mainly trades distortion against plastic accommodation: clamping suppresses camber and angular tilt (≈3 mm → ≈0.5 mm; <1°), but the final stress magnitudes remain within ∼5% of the free condition. Collectively, these results provide new insight into how solid-state phase transformations in titanium alloys interact with weld stress/strain evolution and resulting texture, with implications for improving fatigue life and dimensional stability in aerospace components.