THE EFFECT OF PARTIAL-PRESSURE OF OXYGEN ON THE TRIBOLOGICAL BEHAVIOROF A NICKEL-BASED ALLOY, N80A, AT ELEVATED-TEMPERATURES

In this study, the frictional behaviour and wear of a nickel-based all oy, N80A, as a function of partial pressure of oxygen in a mixture of oxygen and argon at temperatures to 600 degrees C, were investigated o n a pin-on-disk reciprocating sliding wear machine. At temperatures be low 250 degrees C, a maximum was observed in the relationship between wear and partial pressure of oxygen in the environment. However, at te mperatures above 250 degrees C, wear was almost independent of the par tial pressure of oxygen. A transition in friction and contact resistan ce with sliding time was usually observed within the total sliding tim e of 6 h, except in argon below 400 degrees C, where the contact betwe en the pin and the disk was always of metal on metal. The general feat ures of variations in friction coefficient with sliding time at the va rious partial pressures of oxygen were similar to those in pure dry ox ygen at a given temperature, although the transition time increased dr amatically at partial pressures of oxygen below 0.1 atm. Scanning elec tron microscopy observations showed that compact wear debris particle layers were developed at partial pressures of oxygen above 0.1 atm, co rresponding to the transition in friction coefficient with time. Howev er, only very small areas of oxidized smooth load-bearing areas were o bserved at low partial pressures of oxygen and at lower temperatures. The observed experimental results are explained on the basis of a wear model for metals at elevated temperatures. The effect of partial pres sure of oxygen on the tribological behaviour of the alloy has been inc orporated into the model by derivation of relationships for the size a nd generation rate of wear debris particles as a function of partial p ressure of oxygen. Reasonably good agreement between the theory and ex periment results has been obtained. (C) 1997 Elsevier Science S.A.