Lubrication of Metal Surfaces by Oxide Films

Abstract

Experimental data obtained with sixteen metals suggest that hexagonal structured metals have low friction, while other metals have high friction unless a lubricating oxide layer is farmed. In order for an oxide to lubricate, it must not be much harder than the substrate, and the oxide thickness must be adequate. For pin-an-desk tests at loads of about 1 kg, the critical oxide thickness is 10⁻⁶ cm, and the metals must be heated until this thickness is reached. Other solid lubricant films appear to obey the same criteria of not 100 hard, not too thin.