Microstructural and Residual Stress Development due to Inertia Friction Welding in Ti-6246

A thorough investigation has been performed to assess the microstructural properties, mechanical properties (hardness and elastic modulus), and residual stress development in Ti-6Al-2Sn-4Zr-6Mo (Ti-6246) inertia friction welds in the as-welded and postweld heat-treated conditions. It was evident that the thermomechanical deformation in the weld region occurred above the beta transus, forming dynamically recrystallized beta grains and precipitating acicular alpha within the beta grains, which resulted in a localized hardness increase. In the heat-affected zone, a ghost microstructure of the base metal formed because of the absence of sufficient time for diffusion, resulting in Mo segregation in the prior primary alpha plates. Energy-dispersive synchrotron X-ray diffraction and neutron diffraction were used to assess the residual stress development in the three principal directions. The variation in the unstrained lattice parameters across the weld regions was established by imposing a stress balance on the axial stress component in the radial direction. It was found that the maximum stresses occurred in the hoop direction, with significantly lower stresses present in the radial and axial directions. The maximum tensile hoop stresses were located at similar to 4 mm from the weld centerline and not at the dynamically recrystallized beta-rich weld zone. This was associated with the alpha -> beta phase transformation and the subsequent acicular alpha precipitation within the region surrounding the weld centerline.