EFFECT OF WATER-VAPOR IN AIR ON FRETTING WEAR OF PURE METALS

Fretting wear experiments for several pure metals were conducted in air with various relative humidity levels using a hemisphere-on-flat type of fretting apparatus. The materials used were iron, aluminum, copper, silver, chromium, titanium and nickel. Each pure metal had a maximum wear volume at a specific humidity level (RH(max)), which was independent of mechanical factors such as contact load, fretting amplitude and frequency in the range studied. The wear volume at RH(max) decreased with increasing shear strength of the pure metals at high hydrostatic pressures, indicating that adhesive wear was more predominant at RH(max) than abrasive or oxidative wear. The value of RH(max) decreased with increasing standard free energy of oxide formation for the pure metals. This demonstrated that RH(max) was strongly related to the surface chemistry of the pure metals.