The influence of contact conditions on surface reaction layers formed between steel surfaces lubricated by an aviation oil

This study focuses on the influence of load and temperature on the formation and stability of tribo-films for bearing steel on bearing steel contacts lubricated with an aviation oil, EXXON Turbo 2380 (TCP based - tricresyl phosphate) at ambient temperatures. Experiments were carried out on a pin-on-disc (POD) tribometer (with a ball-on-flat geometry) under an average loading rate of 0.17 N s−1 and sliding speed of 3 m s−1. The X-ray photoelectron spectroscopy (XPS) analysis on the worn surfaces of ball and disc shows that a tribo-film forms on both surfaces at room temperature. The formation and removal of the tribo-film are faster on the ball due to the nature of contact between the ball and disc. It was found that the tribo-films formed at room temperature are vulnerable to initial disc temperature. The higher the initial temperature the higher the load carrying capacity. The tribo-film growth and contact deterioration have been monitored by acoustic emission (AE) and electrostatic charge (ESP) sensing systems in real time. The results show that both AE and ESP can detect the tribo-film and contact breakdown and have great potential for on-line condition monitoring of lubricated tribo-contacts.