Surface Softening in Metal - Ceramic Sliding Contacts: An Experimental and Numerical Investigation
Pantcho Stoyanov, Rolf Merz, Pedro Romero, Felix C. Wählisch, Oscar Torrents Abad, Robert Gralla, Priska Stemmer, Michael Kopnarski, Michael Moseler, Roland Bennewitz, and Martin Dienwiebel
ACS Nano 9, 2015, pp 1478–1491
This study investigates the tribolayer properties at the interface of ceramic/metal (i.e. WC/W) sliding contacts using various experimental approaches and classical atomistic simulations. Experimentally, nanoindentation and micropillar compression tests as well as adhesion mapping by means of atomic force microscopy are used to evaluate the strength of tungsten-carbon tribolayers. In order to capture the influence of environmental conditions, a detailed chemical and structural analysis is performed on the worn surfaces by means of XPS mapping and depth profiling along with transmission electron microscopy of the debris particles. Experimentally, the results indicate a decrease in hardness and modulus of the worn surface compared to the unworn one. Atomistic simulations of nanoindentation on deformed and undeformed specimens are used to probe the strength of the WC tribolayer and despite the fact that the simulations do not include oxygen, the simulations correlate well with the experiments on deformed and undeformed surfaces, where the difference in behavior is attributed to the bonding and structural differences of amorphous and crystalline W-C. Adhesion mapping indicates a decrease in surface adhesion, which based on chemical analysis is attributed to surface passivation.