Scuffing resistance after tribosynthesis of a modified surface layer

摘要

In this work, the surface layers of steel samples have been modified by a tribological scuffing process to improve the resistance of the surface to subsequent scuffing failure. In general, scuffing is known to involve large plastic strains and high local temperatures. The scuffed surface layers cool rapidly as heat is transported into the bulk material. This deformation and thermal treatment form highly work-hardened surface layers with small grain size. Resistance to scuffing failure typically improves with increasing hardness; for this reason, we have assessed the scuffing resistance of previously scuffed material as follows. We have modified a high-frequency reciprocating rig tribological tester so that a flat sample can be moved in a direction perpendicular to the direction of reciprocation during a ball-on-flat scuffing test. After initiation of scuffing, each flat was moved at a constant velocity, propagating the scuffing effect sideways from the reciprocating line in order to affect an area. After cleaning, the resistance of such areas to scuffing was measured in a second test. Flats of hardened 440C stainless steel were tested. Contrary to expectations, the resistance of tribosynthesized surface layers to subsequent scuffing was significantly degraded compared to as-polished surfaces. In particular, failures in the brun-inQ portion of the test, before the load was fully applied, were more common when testing tribosynthesized surface layers. The most likely cause was the significantly increased roughness of the modified surface.