Tribological Behavior of a Cr₂O₃ Ceramic Coating/Steel Couple Under Dry Sliding and Heavy Loading Conditions

This work evaluates the effects of heavy loadings on a Cr₂O₃ 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, microhardness and x-ray diffractometry (XRD). The friction coefficient was directly calculated by the tribometer. The wear rate of Cr₂O₃ ceramic coating was evaluated by the wear volume and that of pins by weighing them before and after tests. The wear tracks on pins and coating surfaces were analyzed by XRD 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 mild-oxidational under the lowest constant load, which was therefore suggested as the limit for acceptable performance of the sliding couple under study.