Review of oxidational wear: Part I: The origins of oxidational wear

This is the first part of a two-part in-depth review of the oxidational wear of metals. It discusses the parallelism between the formation of an oxide film for dry contact conditions and of other surface films for lubricated contacct. Wear modes are unified into two major classes of mild and severe wear, including both lubricated both dry and conditions. Oxidational wear is a mechanism of mild wear in which protective oxide films are formed at the real areas of contact (during the time of a contact) at the contact temperature, T_cc. When the oxide reaches a critical thickness ξ, usually 1 to 3 μm, the oxide breaks up and eventually appears as wear particles. These oxides are preferentially formed on plateaux, which alternately carry the load - as they reach their critical thickness - and are removed. Temperature is important in determining the structure of the oxide film present, which in turn affects the wear properties of the sliding interfaces. Hence, this part of the review concludes with a thorough treatment of the thermal aspects involved during the sliding of a typical laboratory simulation of the oxidational wear of steel specimens without lubrication. This treatment shows how the general surface temperature (T_s) and the division of heat (?)_at the interface can be calculated and used, in conjunction with the measured wear rate (w), to give information about a possible surface model consisting of N contracts on the (thermally expanded) operative plateau, the height of the plateau being identical to the critical oxide film thickness (ξ) mentioned above.Part II outlines recent research to determine the oxidational constant, ie the activation energy and the Arrhenius constant, relevant to oxidational wear. It is found that the Arrhenius constant for oxidational wear is different from that for static oxidation tests. Some typical values of N, ξ and T_c are calculated from oxidational wear experiments. A new oxidational wear theory designed to take into account the oxide growth which occurs at the general surface temperature, T_s (where T_s < T_c) , whilst operation plateau is out-of-contact. This theory is most relevant to weat at elevated temperatures, where it is not permissible to assume that out-of-contact oxidation is negligible. After a brief review of the small amount of work done on the effects of partial oxygen pressures on oxidational wear, Part II concludes with a discussion of the possible connection between the general oxidational wear theory for dry contacts and the wear which occurs at lubricated contacts.