The Effect Local Residual Stress States on The Internal Pore Growth in Laser-Welded Ti6Al4V

The micron scale local residual stress states in laser-welded Ti6Al4V were characterized with focused ion beam ring-core milling coupled with digital image correlation (FIB-DIC), and its effect on the growth of welding porosity under external loading was investigated by <i>in-situ </i>tension under X-ray computerized tomography (CT). The internal pores were found to preferentially distribute along the fusion zone boundary and the weld centerline. FIB-DIC and X-ray diffraction indicated high-level tension in the vicinity of the fusion zone, balanced by the long-range compression in the base metal. Comparison with stress-free counterparts showed the residual stress significantly prepone the growth of the pores, whose aspect ratio and volume exhibited observable increments at low applied stresses. On the contrary, the pores without residual tension remained nearly undeformed until the yield point, and the relative tensile strain across the fusion zone showed a similar trend. The results demonstrated that the response of internal welding defects towards external load strongly correlates to the local residual stress states, and highlights the importance of precise measurements of the residual stress states in characteristic regions for applicational titanium laser welds.