Surface Film Formation and Metallic Wear

Abstract

The interactions between surface asperities which occur during sliding are of primary importance in both friction and wear. In consequence, many of the phenomena observed during investigations into the nature of friction should have their counterpart in wear. An experimental study is described of the way in which wear is affected by factors already known to influence friction. It is shown that when a relatively soft metal slides on a harder one, the relationship between the wear and the sliding distance may be one of three general types. Each type is associated with the formation of a surface film during sliding. The extent to which these films (oxide, adsorbed boundary lubricant, etc.) prevent intermetallic contact influences the relationship between the wear rate and the applied load. With several metals there is a discontinuity in the wear rate‐load relationship, and two distinct regimes of wear are obtained. The transition between these two regimes is associated with the breakdown of a protecting surface film. Finally, it is suggested that the generation of protective surface films during sliding comprises an essential part of the ``running‐in'' process of machinery.