Characterization of lubricated worn surfaces using a nano/micro-indenter

Evaluation of wear behavior under lubricant condition could be time consuming, since the material loss may be so small that no significant difference in the protection efficiency between two different lubricants could be determined. Attempts were made to explore potential application of a nano/micro-indenter in characterization of lubricated worn surfaces. In this work, indentation tests were performed on three worn surfaces of a stainless steel experienced unlubricated wear, wear in an anti-wear lubricant oil and in a degraded lubricant oil, respectively. The three worn surfaces showed different responses to indentation. Irregular load–depth curves, such as those with kinks, were observed, and the probability for occurrence of such irregularity depended on the lubrication condition. Different fluctuations in the mechanical behavior of these worn surfaces were observed. The different responses of the worn surfaces to indentation were investigated by examining their morphologies in combination with a modeling study employing the finite element method (FEM). It was demonstrated that a good lubricant led to a relative homogeneous worn surface with less defects, which could be well characterized using the nano/micro-indentation test.