Scuffing is one of the most problematic failure mechanisms and yet the least understood phenomenon in lubricated sliding mechanical components, specifically for those tribological systems working under starved lubrication conditions. It occurs suddenly and often results in loss of component functionality, and thus high repair costs. Studies on scuffing have been ongoing for almost 80 years, and several hypotheses and predictive theories have been proposed over these years. Despite these efforts, a large degree of uncertainty still exists and no satisfactory model for scuffing prediction has yet been developed. This is due to a lack of fundamental understanding of scuffing and the mechanism of scuffing initiation [1,2]. In the present study, a cast iron-steel tribo-system working under starved lubrication conditions with the dominant scuffing failure mechanism is investigated. Reciprocal lubricated sliding tests having flat on flat condition were carried out for the cast iron-steel tribo-pair at a constant pressure of 24 MPa and a frequency of 6 Hz. To enter the boundary and starved lubrication conditions, limited amount of lubricant was homogeneously sprayed onto the cast iron surface by a precise spray technique. The tribo-film formed on the contact surface of cast iron, the scuffed region, and the materials transferred to the steel counter-body due to scuffing were analyzed using SEM, TEM, and EELS techniques. Based on the experimental observations in this work, a new theory is proposed for initiation of scuffing in this cast iron-steel tribo-system. According to this theory, scuffing initiates when the tribo-film iron oxide reduces to ?-iron providing metal-metal contact and, consequently, strong adhesion between the sliding surfaces. The reduction of the oxide takes place due to a temperature increase at the contacting asperities together with the presence of carbon, coming from either the lubricant or graphite flakes of cast iron, as the reducing agent.
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 W.F. Bowman, G.W. Stachowiak, Tribol. Lett. 2 (1996) 113–131.