Responses of an atmospheric plasma sprayed (APS) alumina-titania coating to scratch

An alumina-titania composite coating was produced using a thermal plasma spraying coating process. As-sprayed coating microstructures were observed using scanning electron microscopy and energy dispersive spectroscopy. A scratch test was conducted on the finely-polished coating under conditions of constant loading speed and moving rate. Acoustic emissions as well as scratching coefficient were measured during scratching. During the cyclic scratching, the APS coating showed fatigue. The transition from plastic deformation to fracture was time-dependent and it was also accelerated with an increase of the applied normal load. During plastic deformation, fine wear debris resulted from grain crushing while the flake-like large debris was formed due to the initiation and propagation of microcracks during fracturing. The major defects in the microstructures gave different wear debris. Fine particle formation was promoted by discontinuities whereas flake debris was mainly due to the intersplat pores between splats and vertical cracks in the splat.