Influence of Black Oxide Coating on Micropitting and ZDDP Tribofilm Formation

Micropitting is a type of surface fatigue damage that occurs in rolling–sliding contacts operating under thin oil film conditions. Application black oxide (BO) coating to steel rubbing surfaces has been suggested as potential approach alleviate micropitting. This article confirms BO coatings can prevent micropitting and identifies the predominant mechanism by which this occurs. tests were carried out using zinc dialkyldithiophosphate (ZDDP) solutions ball-on-disc tribometer. was preferentially generated on smooth balls completely prevented applying rougher discs, regardless whether coated or not. In contrast, when rough discs not BO-coated, consistently both BO-coated uncoated balls. about one-quarter hardness used found be very rapidly removed from asperity peaks at onset rubbing, despite presence ZDDP. resulted an almost immediate large reduction roughness high stresses would normally initiate propagate cracks, leading Parallel measurement showed did suppress tribofilm growth, so ZDDP able protect against adhesive wear while promoting The insights presented here help with design components lubricants are effective controlling sliding