Tribology of tungsten disulfide-nanocrystalline zinc oxide adaptive lubricant films from ambient to 500 degrees C

Tungsten disulfide (WS2)-zinc oxide (ZnO) composite is a candidate material that exhibits adaptive lubricant behavior. Adaptive lubricants undergo che mical changes with changing environment to provide lubrication in extreme e nvironments. In the current study, the tribological characteristics of WS2- nanocrystalline ZnO films have been investigated from ambient to 500 degree s C. The composite films were powder burnished on inconel substrates. Using a bah-on-flat tribometer, friction tests were conducted on WS2-ZnO nanocom posite films containing 50% by weight of the oxide. For comparison, measure ments were made on pure WS2 films burnished under identical conditions. The room temperature tests were performed in dry nitrogen, while the elevated temperature tests were run in air. Wear scars and transfer films on the cou nterface were analyzed by scanning electron microscopy, energy dispersive X -ray spectroscopy and Raman spectroscopy. Results showed that the nanocryst alline ZnO additive resulted in significant reduction in friction coefficie nt of WS, both at 300 degrees C as well as at room temperature. Third-body analyses from 300 degrees C tears revealed that tribooxidation is less prev alent in nanocomposite films. At 500 degrees C, the friction coefficient of pure WS2 films increased to 0.50 within the first 2000 cycles, whereas the nanocomposite films lasted the. entire duration of 10,000 cycles with stea dy state friction coefficient of 0.22. Raman spectroscopy identified the fo rmation of zinc tungstate (ZnWO4) during the 500 degrees C triborests, conf irming the adaptive lubricant concept in WS2-ZnO nanocomposites. (C) 2000 E lsevier Science S.A. All rights reserved.