Microstructure and tribological properties of low-pressure plasma-sprayed ZrO2-SaF(2)-Ag2O composite coating at elevated temperature

Microstructure and tribological properties of low-pressure plasma-sprayed ( LPPS) ZrO2-CaF2-Ag2O (ZFA) composite coating were studied by means of optic al microscope, scanning electron microscope (SEM) with energy dispersive X- ray analysis (EDXA), electron probe microanalyzer (EPMA) and high-temperatu re reciprocating wear tester. Coating selected for this investigation was 8 wt.% Y2O3 partially stabilized zirconia coating doped with CaF2 and Ag2O a s the solid lubricants. The as-sprayed ZFA coating exhibits a typical lamel lar structure of ZrO2 and CaF2 constituents, and some amounts of isolated A g2O particles. ZFA coating possesses a distinct improvement in wear resista nce and frictional characteristics as compared to yttria partially stabiliz ed zirconia (YPSZ) coating at elevated temperatures. At 300-700 degreesC, t he ZFA coating exhibits lower friction and wear than at room temperature, 2 00 or 800 degreesC. Ag2O and CaF2 acting as solid lubricants effectively at 300-400 and 600-700 degreesC, respectively, reduce the friction of the com posite. But with the increase of temperature up to 800 degreesC, the severe adhesive sliding causes more material transfer and tearing-out of coating, and finally leads to a high friction and wear. The change or wear transiti on from a microcrack- or microfracture-controlled wear at room temperature and 200 degreesC to plastic deformation- and adhesion-controlled wear at el evated temperatures is quite distinct and is accompanied by a great change in both friction coefficient and wear loss (such as those at 300 or 800 deg reesC). (C) 2001 Elsevier Science B.V. All rights reserved.