Residual stress, mechanical properties, and grain morphology of Ti-6Al-4V alloy produced by ultrasonic impact treatment assisted wire and arc additive manufacturing

Ultrasonic Impact Treatment (UIT) is an effective technique for surface refinement and residual stress reduction, which is widely used in welding. This study investigates UIT-assisted Wire and Arc Additive manufacturing (WAAM). The residual stress, grain morphology and mechanical properties of post-UIT and as-deposited samples are studied. The result demonstrates that the UIT has a significant influence on the decrease of the residual stress. Moreover, the residual stress of the post-UIT samples is much lower than that of the as-deposited samples. The samples fabricated by UIT-assisted WAAM have a novel, bamboo-like distribution of prior-β grains, an alternating distribution of short columnar grains and equiaxed grains. The grain size of this bamboo-like structure is much smaller than the coarsen columnar grains. In addition, the mechanical properties of the post-UIT and as-deposited samples are compared. The results indicate that the average tensile strength of the post-UIT samples is higher, while the average elongation of the post-UIT samples is lower.