Dry Friction of Oxide Ceramics Against Metals: The Effect of Humidity

Abstract

Reciprocating friction experiments were conducted to determine the effect of humidity on the friction characteristics of oxide ceramics slid against pure metals. Aluminum oxide and zirconium oxide had similar friction properties against metals. The friction coefficients of the oxide ceramics were affected by the type of metal (the chemical activity of the metal) and the relative humidity (RH). Especially in highly humid air, the friction coefficients were well correlated with the Gibbs free energy of ionization of the metals; that is, the more active metals showed higher friction coefficients. This result was considered to be attributable to the metal oxides caused by an oxidizing atmosphere (highly humid air). Another experiment in which Ti specimens with preoxidized surfaces were slid on the ceramic specimens was carried out, and the enhancing effect of the surface metal oxides on adherence characteristics was confirmed. On the other hand, the lubricative effect of water adsorbed on the surfaces of the specimens was confirmed by the experiment in which the Ag specimens were slid on the ceramics for specific time intervals.