Fretting wear characterization by point contact of Nickelsuperalloy interfaces

Fretting wear is a complex phenomenon that occurs at component interfaces that are subjected to low amplitude oscillation under high contact pressure. In turbomachinery fretting also occurs at the blade tip interfaces where shrouds, are machined. To diminish the fretting damage coatings are applied to the blade tips. The aim of this study is to compare the fretting wear behaviour of single crystal CMSX4 superalloy interfaces both with and without plasma sprayed T-800 coating. Experiments were conducted with a nominal spherical surface which was pressed against a flat surface of the same material at a temperature of 800°C. The mating surfaces were worn with an alternating relative displacement with an amplitude of 30μm, at a frequency of 100Hz. The hysteresis cycles, namely the tangential contact force against the relative displacement, were measured throughout the experiment. The comparison of the hysteresis cycles showed that the tangential contact stiffness of the coated surfaces is greater than that of the uncoated surfaces while the friction coefficient of the coated surfaces was lower than that of the uncoated. At the end of the wear process, the mating surfaces were measured by three-dimensional optical interferometry and observed through a SEM analysis. After 10×106 wear cycles, the uncoated surfaces showed a large change in the contact parameters and fretting cracks on the flat surface. In contrast, the coated surfaces did not show a measurable change in the contact parameters, while the coating damage on the flat surface would lead us to predict incipient catastrophic wear.