Adaptation and self-healing effect of tribo-oxidizing in high-speed sliding friction on ZrB2-SiC ceramic composite

The objective of this work was to study adaptive mechanisms and behavior of ZrB2-20 vol% SiC ultra high-temperature ceramics in low-speed and high-speed sliding against a high-carbon steel disk. The worn surfaces of ceramic samples were examined and characterized for chemical composition and mechanical properties. Intense tribooxidation of the composite components as well as transfer layer generation was observed at sliding speeds as high as 11 m/s, 22 m/s and 37 m/s with the formation of at least two subsurface layers. The first one was a mechanically mixed (transfer) layer composed of an iron-containing borosilicate glass mixed with the tribooxidation products resulted from oxidizing both ceramics and steel components. The second underlying layer was a partially oxidized zirconium diboride. Such a combination of quasi-viscous transfer layer and partially ductile underlying layer allowed reducing friction, forming a smooth worn surface and protecting the ceramics against brittle subsurface fracture. Also the effect of self-healing of the subsurface defects by means of liquid bomsilicate glass was observed during sliding friction. The results obtained were discussed in comparison to other adaptation mechanisms found in different materials during friction.