Effect of sliding speed and contact pressure on the oxidative wear of austempered ductile iron

The dry tribo-oxidative sliding wear of an ADI was investigated as a function of sliding speed and applied pressure, using a pin-on-disc apparatus. The wear rates, steady-state friction coefficients and contact temperatures were measured for each sliding conditions, and the acting wear mechanism were investigated by means of metallographic observations of worn surfaces and subsurface damaged regions. Two friction and wear regimes were identified. In the first one, at low sliding speeds (0.5-1 m/s), friction coefficient and wear rates were found to decrease with sliding speed and applied pressure. In the second one, at high sliding speeds (1.5-2.6 m/s), friction and wear were found to decrease with sliding speed but to increase with applied pressure. The observed behaviour and the transition from the low-sliding speed regime to the high-sliding speed regime were explained by considering the formation of a surface white layer that is controlled by the attainment of a critical flash temperature during sliding.