Wear Behaviour of a Plasma-Sprayed Al2O3-13%TiO2 Ceramic Coating/Steel Couple under High Constant and Variable Loads

This work investigates the effects of heavy loadings on an Al2O3-13%TiO2 ceramic coating/steel couple under dry sliding and in conditions similar to those occurring in heavy-duty diesel engines. Two types of wear tests were performed by a standard pin-on-disc tribometer under high constant and variable loads. Before wear tests, microstructure and mechanical properties of coating and steel were determined by optical emission spectrometry, optical microscopy, roughness, hardness, fracture toughness, elastic modulus and X-ray diffractometry. The coefficient of friction was instantly calculated by the tribometer. The wear rate of Al2O3-13%TiO2 ceramic coating was evaluated by the wear volume and that of pins by weighing them before and after the tests. The wear depth of pins was calculated by measuring the decrease in length by calipers before and after the tests. The wear tracks on pins and coating surfaces were analyzed by X-ray diffractometry and by scanning electron microscopy with energy-dispersive spectroscopy. For all loads except the lowest constant one, the results indicated high friction and wear involving material removal from the coating surface, through a severe-oxidational wear associated with extensive cracking of the surface of the coating, softening of the carburizing steel and removal of the carburized layer of pins. The wear mechanism was between mild- and severe-oxidational under the lowest constant load, which was therefore suggested as the limit for acceptable performance of the sliding couple under study.