Tribological properties of adaptive nanocomposite coatings made of yttria stabilized zirconia and gold

Composite coating architectures where hard nanocrystalline grains are embed ded in an amorphous matrix provide considerable improvement in hardness, to ughness, wear resistance, and environmental adaptation. Using this concept, nanocrystalline yttria stabilized zirconia (YSZ) was embedded in an amorph ous YSZ/Au matrix to address problems with YSZ ceramics in sliding wear. Th e coatings were produced by a hybrid of laser ablation of YSZ and magnetron sputtering of Au. Coating composition and microstructure were investigated using a number of analytical techniques, and correlated with results of sl iding friction tests at 25 and 500 degreesC. In situ transmission electron microscope imaging of microstructure evolution during a temperature cycling from 25 to 500 degreesC was performed to explain changes in tribological p roperties. In comparison to YSZ ceramic, YSZ/Au coatings were tougher, form ed less wear debris, and reduced friction coefficients from 1.0 to 0.3-0.4 at 25 degreesC and to 0.2 at heating to 500 degreesC. Improvements in tribo logical properties were related to the microstructure adaptive changes at e levated temperatures and formation of lubricating Au transfer films. (C) 20 01 Elsevier Science B.V. All rights reserved.