The effect of an alumina counterface on friction reduction of CuO/3Y-TZP composite at room temperature

The friction behavior of CuO/yttria-stabilized tetragonal zirconia (3Y-TZP) composite in dry sliding against alumina at room temperature has been investigated. The results show that an alumina counterface has a crucial role on the frictional behavior when sliding against CuO/3Y-TZP composite in comparison with other counter materials. Pure 3Y-TZP shows high friction and wear under the same conditions. It is found that the friction reduction behavior is dependent on the sliding test conditions such as load and humidity. A thin aluminum-rich layer less than 200 nm thick on the contact surface during the low friction situation has been found by various analyzing techniques including interference microscopy, micro-Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microcopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The induced change of contact conditions and interfacial chemical reaction between CuO and alumina to form the phase CuAlO2 increase the wear of alumina and accelerates the formation of an aluminum-rich surface layer. The presence of such a layer in the contact is beneficial for reducing friction. After a certain sliding distance, the coefficient of friction shifts from a low value to a high value due to a change in the dominating wear mechanism. This transition is shown to be caused by a different composition and thickness of the interfacial layer.