Effects of Shot-Peening on Fretting-Fatigue Behavior of Ti-6Al-4V

Abstract

The effects of shot-peening on the fretting fatigue behavior of titanium alloy, Ti-6Al-4V were investigated. Specimens were shot-peened as per AMS 2432 standard. X-ray diffraction analysis measured a maximum compressive stress of 800 MPa at the specimen surface, which reduced to zero at a depth of 188 μm. The compensatory residual tensile stress in the specimen was estimated using a curve fitting technique, the maximum value of which was found to be 260 MPa at a depth of 255 μm. Fretting fatigue tests were conducted at room temperature at a cyclic frequency of 200 Hz. Scanning electron microscopy of the shot-peened fretting fatigue specimens showed that the crack initiated at a point below the contact surface, the depth of which was in the range of 200–300 μm. Finite element analysis of the fretting fatigue specimens was also conducted. Fatigue life diagrams were established for the fretting fatigue specimens with and without shot-peening, and were compared to those under the plain fatigue condition, i.e. without fretting. Shot-peening improved the fretting fatigue life of Ti-6Al-4V; furthermore, it moved the crack initiation site from the fretting contact region to a region inside the specimen. Moreover, stress analysis showed that the fatigue failure of shot-peened specimens was caused by the compensatory tensile residual stress.