A review of the influence of environmental humidity and water on friction, lubrication and wear

A review is given of the various ways in which humidity and liquid water can influence the friction and wear of metals, polymers, carbons and graphite, lamellar solid lubricants and ceramics. Compared with dry sliding, water usually reduces friction of materials to a limited extent, except for MoS2, but wear rates change depending on the materials concerned. Most of the fundamental mechanisms involved appear to be reasonably well understood, but uncertainties still remain concerning the role of humidity on the formation of third-body layers of aggregated wear debris.