A miniature three-contact disc machine was employed to reproduce micropitting under controlled condition and study the effect of lubricant composition on the phenomenon. In this preliminary work, a PAO base stock was tested on its own and with a ZDDP anti-wear additive. Micropitting only occurred when the ZDDP was present. During the tests, the roughness of the counterface was found to decline gradually. When the ZDDP was present, the roughness declined more slowly. The results suggest that certain anti-wear additives may be detrimental to micropitting resistance simply because they prevent wear rather than by any direct influence on micropitting.
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