Friction and wear at various oxygen concentrations in the contact zone

Summary

• 1. The oxidation intensity and properties of secondary structures formed in the friction zone depend upon the oxygen content of the ambient atmosphere.

• 2. In studies of the role of oxygen in sliding friction it is advisable to carry out tests in air at 760–10⁻⁵ mm Hg. If the oxygen content of the ambient atmospher is higher than that of air at atmospheric pressure, oxidation processes are the predominant factor in friction between metal surfaces; the intensity of these processes is practically unaffected by further increases in oxygen concentration. When the air pressure (and, consequently, the oxygen concentration) is reduced to 10⁻¹ mm Hg, seizure comes into play; its intensity increases as the air pressure is further reduced and reaches its maximum at 10⁻⁵mm Hg.

• 3. In the oxygen concentration range corresponding to air pressures ranging from 760–10⁻⁵mm Hg there is an inversion of the effect of oxygen upon the qualitative and quantitative characteristics of friction and wear. For instance, a minimum intensity of wear of steel under dry friction conditions is observed in air at 10–1 mm Hg; it increases both above and below this pressure range.

• 4. Under conditions of high oxygen deficiency the physical and mechanical properties of steel play the predomiant part in friction and wear, the role of chemical reactions being of no practical importance. The effect of heat generated by friction is particularly pronounced at low oxygen concentrations, at which both friction and wear depend primarily upon the mechanical, thermal and physical properties of the steel and upon the heat-induced changes in these properties, because it is precisely under these conditions that the interaction between clean oxide-free metal surfaces takes place.

• 5. Analysis of the role of oxygen in sliding friction opens up possibilities of controlling friction and wear-resistance of friction pairs by controlling the oxygen concentration in the friction zone, utilizing the beneficial effect of heat and taking into account the predominant role of the mechanical properties of steel under friction at low oxygen concentrations. An important, although insufficiently investigated, factor in controlling friction and wear is the peculiarity of the chemical reactions in the friction zone: the suppression of these processes at high, and their intensification at low oxygen concentrations.