Subsurface multilayer evolution of ZrB2–SiC ceramics in high-speed sliding and adhesion transfer conditions

Abstract

High-speed continuous sliding experiments on ZrB2-20 vol% SiC ultra-high temperature ceramics have been carried out to elucidate specifics and details of tribooxidation under conditions of subsurface deformation and friction generated heating. Subsurface multilayer structure layer phase composition was obtained to testify on the intense mass transfer processes. Generation of thick boron-depleted and mechanically mixed layer (MML) composed of silicate glass, iron, high-temperature zirconia phases as well as silicon carbide insulated the underlying ZrB2 grains and served to generation of two transition layers composed of borosilicate glass, zirconia and iron oxyborides. This and sealing the voids and cracks by borosilicate glass had its effect on oxidation of silicon carbide grains, which might have caused intense formation of spherical particles even far below the worn surface. Mass transfer of iron and oxygen into ceramic composite grains has been discovered along with evaporation of boron anhydride from the MML.