Fretting wear of micro-arc oxidation coating prepared on Ti6Al4V alloy

Micro-arc oxidation (MAO) coating was prepared on Ti6Al4V alloy surface and its characterizations were detected by Vickers hardness tester, profilometer, scanning electric microscope (SEM), energy dispersive X-ray spectrometer (EDX) and X-ray diffractometer (XRD). Fretting wear behaviors of the coating and its substrate were comparatively tested without lubrication under varied displacement amplitudes (D) in a range of 3-40 μm, constant normal load (Fn) of 300 N and frequency of 5 Hz. The results showed that the MAO coating, presenting rough and porous surface and high hardness, mainly consisted of rutile and anatase TiO2 phases. Compared with the substrate, the MAO coating could shift the mixed fretting regime (MFR) and slip regime (SR) to a direction of smaller displacement amplitude. In the partial slip regime (PSR), lower friction coefficients and slight damage appeared due to the coordination of elastic deformation of contact zones. In the MFR, the friction coefficient of the coating was lower than that of the substrate as a result of the prevention of plastic deformation by the hard ceramic surface. With the increase of the displacement amplitude, the degradation of the MAO coating and the substrate increased extremely. The fretting wear mechanisms of the coating were abrasive wear and delamination with some material transfer of specimen. In addition, the coating presented a better property for alleviating fretting wear.