Influence of humidity on the fretting wear of self-mated tetragonal zirconia ceramics

The influence of different humidity levels on the tribological behaviour of polycrystalline tetragonal zirconia polycrystals (Y-TZP) sliding against c ommercial Y-TZP balls has been investigated. Fretting experiments (mode I) have been conducted at three different relative humidity (RH) levels, namel y 5%, 50% and 85% RH. Based on the obtained wear and friction data as well as the morphological investigation of the worn surfaces, the wear mechanism s in different humidity conditions are proposed. The morphology of the wear pits suggests that plastic deformation coupled with delamination is the we ar mechanism in dry sliding (5% RH) and in ambient humidity (50% RH) condit ions. Additionally, Raman measurements showed that the phase transformation of tetragonal zirconia phase to monoclinic symmetry also plays a role in t he fretting wear under all the investigated humidity conditions. XPS analys is of the wear debris formed at 85% RH indicates that tribochemical wear is the dominant wear mechanism at high humidity conditions. (C) 2000 Acta Met allurgica Inc. Published by Elsevier Science Ltd. Ail rights reserved.