Multiscale residual stress heterogeneity in microtextured Ti–6Al–4V after quasi-static plastic deformation

Residual stresses are known to influence the structural integrity of components and are generally multiscale in nature for polycrystalline metals. Residual stresses vary at the grain level, particularly for hexagonally close packed (HCP) materials like titanium, due to their strong elastoplastic anisotropy. Titanium alloys, like Ti-6Al-4V, also often contain macrozones or microtextured regions (MTRs), which are clusters of HCP grains with similar orientation that are linked to fatigue crack nucleation. In this investigation, the multiscale residual stress distribution induced by quasi-static deformation of Ti-6Al-4V is quantified, with the aim of distinguishing variation at the scale of MTRs and at the scale of individual grains. Four-point bending was used to induce a controlled macroscale residual stress distribution in bar specimens sectioned from an annealed plate along the rolling and transverse directions. Synchrotron X-ray diffraction reveals mesoscale residual stress deviations from the macroscale value of up to 100 MPa, which are attributed to local MTR transitions. Furthermore, focused ion beam – digital image correlation (FIB-DIC) is used to evaluate the variation of microscale residual stresses. These grain-level residual stresses show significant scatter, and can deviate from the macroscale value by several hundreds of MPa, with no pronounced dependency on crystallographic orientation. These findings provide experimental validation of the critical role of MTRs and microstructure in governing the residual stress distribution in Ti-6Al-4V. Therefore, this study illustrates that even simple quasi-static deformation can lead to significant multiscale residual stress heterogeneity, which may affect the structural integrity of components subjected to more dynamic loading.