An experimental study of the friction of metals which have been coated with inorganic films by reaction with their surrounding atmosphere. The specimens are first cleaned at high temperature in vacuo and then heated in the selected reactive vapor. Many coatings will prevent seizure and give a fairly constant but high coefficient of friction up to high temperatures. Layer-lattice compounds such as MoS2, CrCl3, and TiI2 give much lower friction at all temperatures below those at which the film decomposes or evaporates (about 850 C for molybdenum disulphide). A film of boron nitride formed on boron shows a high intrinsic friction, but this can be reduced by certain vapors or by raising the temperature above about 800 C. Most of the experiments were performed with very light loads but the films are shown to be effective under kilogram loads. A simple indentation test capable of selecting lubricants under loads up to 12 tons is described. This shows that a film formed by heating stainless steel in CCl2F2 will lubricate at 400 C when the steel is deformed by over 50 per cent.

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