The influence of water vapour in air on the friction behaviour of pure metals during fretting

Abstract

An investigation was conducted to determine the effect of water vapour content in air on the frictional behaviour during fretting of pure metals: iron, aluminium, copper, silver, chromium, titanium and nickel. The fretting experiments were carried out under various humidity levels, ranging from dry air to 50% relative humidity at 23°C. During the experiment the frictional force between fretting surfaces was measured. Pure metals, except iron, were found to have a maximum value of the coefficient of friction during the steady-fretting stage ( μ s ) at a specific humidity (RH max). Iron showed a rapid decrease in μ s with increasing humidity at RH max. Each pure metal also exhibited maximum fretting wear at RH max. The value of μ s at RH max for each metal was strongly related to the heat of formation of the lower metal oxide, indicating that the adhesive contact area was larger at RH max for the fretting of metals with less chemical activity. At high humidity levels water vapour generally reduced the coefficient of friction, μ s .