SOME FRICTIONAL FEATURES ASSOCIATED WITH THE SLIDING WEAR OF THE NICKEL-BASE ALLOY N80A AT TEMPERATURES TO 250-DEGREES-C

The time-dependent variations of friction coefficient and the contact resistance of a nickel-base high-temperature alloy, N80A, during like- on-like sliding in pure oxygen at temperatures of 20-250-degrees-C wer e simultaneously recorded and the tribological behaviour correlated wi th the nature of the sliding contact. A transition to a positive conta ct resistance always occurred after some time of sliding in the temper ature range investigated. However, the time-dependent variations of co efficient of friction showed quite different features at the various t emperatures. Corresponding to the times of the transitions in contact resistance, at 20-degrees-C, the friction coefficient increased to a h igher value from the initial value while, at 250-degrees-C, it decreas ed to a lower value; however, at 150-degrees-C, the coefficient of fri ction remained unchanged after the transition. Scanning electron micro scopy observations have shown that the predominant factor for such dif ferent tribological responses at the various temperatures is the natur e of the contact between the surfaces. At 20-degrees-C, the real conta ct areas mainly consisted of loosely compacted particles while, at 250 -degrees-C, the load-bearing areas were smooth wear-protective oxide l ayers. At the intermediate temperature, 150-degrees-C, the load-carryi ng areas comprised both types of contact. A mathematical model has bee n proposed and is used to relate the frictional behaviour to morpholog ical features of the wear surfaces developed at the various temperatur es.