Improvement of Fatigue Strength of 3D-Metal by Combined Process of Blasting and Cavitation Peening

Three dimensional additively manufactured metallic materials, i.e., 3D-Metal, are attractive materials. However, the fatigue strength of as-built 3D-metal is nearly half of bulk metals. In order to enhance the fatigue strength of 3D-metal, a combined process of blasting and cavitation peening (CP) was proposed. In the process, the blasting makes smoother surface by collisions of abrasives, and introduces compressive residuals stress in the sub-surface region. After the blasting, CP using a submerged water jet introduces compressive residual stress into the deeper region. In the present paper, titanium alloy Ti6Al4V manufactured by direct metal laser sintering (DMLS) was treated by the combined process of blasting and CP. The fatigue strength was evaluated by torsion fatigue testers of a torsion-controlled type and an angle-controlled type. To make clear the mechanism of the improvement of fatigue strength, surface roughness and surface residual stress were measured. It was revealed that the blasting introduced the compressive residual stress while decreasing the surface roughness, and the fatigue strength was improved by about 33% compared with as-built specimen. When the specimen was treated by CP after blasting, the fatigue strength was improved by 58%, which was larger than that of CP only.