Subsurface characterization of ZrB2–20 vol % SiC ceramic after high-speed sliding

Abstract

The objective of this work was to study the subsurfaces of ZrB2–20 vol % SiC ultra high-temperature ceramics after high-speed sliding against a high-carbon steel disk. Intense tribooxidation of the composite components as well as transfer layer generation was observed at sliding speeds as high as 11, 22 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 contained 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 borosilicate glass was observed during sliding friction.