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Abstract
The Composition of the surface coatings obtained by running commercially available crankcase oils in the four-ball wear tester was determined using a scanning Auger microprobe. The films were 300–500 nm thick, highly heterogeneous, and composed primarily of iron, oxygen, and calcium, plus smaller amounts of zinc, phosphorus, sulfur, and carbon. There were two types of regions within the wear scars, one rich in sulfur and either iron or zinc, the other in calcium, phosphorus, and oxygen. Due to low carbon levels and evidence from other investigations, the sulfur-rich regions were thought to contain a combination of iron and zinc sulfides. The composition of the phosphorus compounds could not be determined, but the data suggest that phosphorus was combined with oxygen as phosphate or phosphate-like species.