Investigations of the effects of combination treatments on the fretting fatigue resistance of GH4169 superalloy at an elevated temperature

In this work, a novel combination treatment was investigated as a means to improve the rotating bending fretting fatigue resistance of GH4169 superalloy at 650 degrees C. The properties, morphologies and composition were studied for magnetron-sputtered WS2/Ti films on substrates with and without a shot peening pre-treatment. The surface integrity and fretting fatigue performances at 650 degrees C were tested and compared for untreated, shot peened and combinedly treated specimens. The experimental results evidenced the significant role of shot peening pre-treatment in the adhesion behavior of oxidized films at elevated temperature. Furthermore, shot peening and magnetron sputtering were expected to have a synergistic effect to improve fretting fatigue resistance at elevated temperature. According to the surface integrity characterization and fretting fatigue tests, the surface hardened layer and the compressive residual stress fields induced by shot peening improved the fretting fatigue limit by 29%, and the average life was 12.4 times as that of the untreated specimens when the fatigue load was 600 MPa. The positive effect was attributed to the resistance properties during the initial adhesive wear stage, reduction of crack initiation and propagation and probable formation of a third body layer. Moreover, the films further increased the fretting fatigue life by 1.6 times compared with that of the shot peened specimens. The effectiveness of shot peening was retained, and the additional lubrication effect facilitated a more stable third body layer, which resulted in a longer fretting fatigue life.