Fretting wear of self-mated tetragonal zirconia ceramics in different humidity

Humidity is reported to have a considerable influence on the tribological behaviour of engineering ceramics. This paper reports on fretting wear experiments (mode I, reciprocating sliding) with self-mated polycrystalline tetragonal zirconia (Y-TZP) ceramics under dry, ambient and humid conditions. Based on the friction and wear data as well as the morphological investigation of the worn surfaces, the wear mechanisms under different humidity conditions are elucidated. It is unequivocally demonstrated that high humidity (85-90 % RH) significantly reduces friction and wear of self-mated Y-TZP ceramics. The morphology of the wear pits indicates that tribomechanical wear via cracking induced spalling is the major wear mechanism in dry and ambient humidity conditions. XPS analysis of worn surfaces revealed that the cause for the lower friction and wear under high humidity conditions is the formation of a lubricious hydroxide layer.