Transition wear behaviour of IC-50 ordered alloy

The friction and wear behaviour of work hardened Ni₃AI based IC-50 ordered alloy dry sliding against an AISI M2 tool steel was studied. Block on disc wear tests were performed by applying loads ranging from 50 to 800 N at a constant sliding velocity of 0.628 m S^-l. The sliding distance dependent tribological transitions were monitored through friction and surface temperature measurements. In every test an initial running in friction peak independent from the applied load was observed. It originated mainly from the abrasive action of the surface oxides initially present in the counterface steel. A second tribological regime characterised by metallic wear (abrasion of the tool steel carbides and adhesion) followed. This tribological regime is the only such regime observed for tests at loads up to 100 N. In the case of tests at loads higher than 100 N, a second transition to an oxidative friction and wear regime was observed. A thin NiO oxide film protects the intermetallic alloys from severe wear, whereas the counterface disc shows the maximum wear because of the abrasion from the oxides. Correspondingly, the friction coefficient increases with respect to the previous regime. This tribological regime prevails in the case of the tests at intermediate loads, i.e. at 200 and 300 N. Afourth tribological transition was observed in tests at higher loads (above 400 N). The higher average surface temperature induces surface softening phenomena of the originally work hardened alloy. This causes damage to the oxide layer which no longer protects the alloy. Hence delaminative metallic wear occurs because of intense surface plastic shearing. This tribological regime prevails in the case of tests at the highest adopted loads. If the wear behaviour is considered as afunction of load, two load dependent transitions can be highlighted. The first transition (at about 150 N) is characterised by a reduction in wear and is connected with a transition from metallic (abrasion and adhesion) to oxidative wear. The second transition (at about 350 N) shows an increase in wear determined by the transition to a delaminative wear regime.