Neutron diffraction measurements for the determination of residual stress in Ti6Al4V welded plates

Ti6AI4V is an alloy largely used for aerospace technology. In this work, three plate-shaped specimens have been studied by neutron diffraction, namely a thick walled welded sample (thickness 6 mm), and two thin ones (1.6 and 2 mm thick), in order to investigate the effect of thickness on residual stress states. Experiments have been performed on the D1A diffractometer at the ILL, Grenoble (France) for the 6 and 1.6 mm thick specimens and on the E3 diffractometer at the HMI-BeNSc, Berlin, Germany, for the 2 mm thick sample. The unstrained interplanar distance d0 has been evaluated with the plane stress hypothesis for each investigated gauge point. Large variations of d0 have been found inside the heat affected zone (HAZ) and the weld pool, probably due to the grain size, and some composition and precipitation gradients. Basically, lower tensile stresses have been found in the thinnest sample, whereas the stress level is almost the same for the 6 and the 2 mm thick specimens. The strong similarity between the latter two samples is confirmed by the non-zero tensile stress state found far from the weld in both of them. The hoop stress lies always higher than the axial, which oscillate around zero for the 1.6 and the 6 mm samples.