Fretting damage of contact interfaces of CMSX-4 with and without T800 coating

Fretting fatigue is a complex phenomenon that occurs at component interfaces undergoing low amplitude oscillation and high contact pressure. In turbomachinery fretting occurs also at the blade tip interfaces where shrouds are machined with the aim to reduce the blade resonant vibration amplitude. The aim of this study is to investigate the damage by fretting on CMSX4 superalloy interfaces with and without plasma sprayed T800 coating. The contact pair is a hemispherical surface on a flat surface. The hysteresis cycles, namely the contact force against the relative displacement, have been measured through the experiment. The worn surfaces have been characterized by three-dimensional optical interferometry and SEM analysis. After 3×10e6 and 10×10e6 fretting cycles the surface without coating shows surface cracks and large change in the contact parameters.