Investigation of Wear by Electron Diffraction

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Abstract
This review of electron diffraction theory and technique emphasizes its scope and limitations in the study of lubrication. The first section describes important areas of wear and friction studies where the electron diffraction method may be used, with examples chosen from the literature. Included in the discussion are: (a) monolayers, liquid lubricants, and greases, (b) polished and amorphous films, (c) the relation to wear of the crystallite size of surface phases, (d) possible relations between wear and the orientation of surface films, (e) solid lubricants, (f) mechanism of extreme pressure lubrication, and (g) the identification of wear debris. The second part of the paper presents the electron diffraction results from three wear studies in the authors' laboratories. Molybdenum isobutylxanthate is an effective extreme pressure oil additive for hard steel. Electron diffraction shows that the anti-wear mechanism may in part be due to the formation of a film containing iron monosulfide. Cast iron top-piston-ring durability in a spark-ignition engine was studied using several fuels which gave widely different wear rates. The composition of the surface layers of worn rings possibly does not depend on fuel additive, but is dependent on test length. The degree of orientation of occluded graphite which has been smeared over the surface is primarily a function of wear rate. Finally, preliminary studies suggest that there may be a relation between ring-bore wear and the crystallite size of the solids of combustion of fuel additives.

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