The sliding wear of ceramics

Abstract

The micromechanical and microchemical processes which take place during the friction of ceramics are not fully understood. The occurrence of surface plasticity and microfracture on a sub-grain size scale have been suggested but no clear experimental evidence has been provided. Tribochemical wear mechanisms are now considered to be critical to the wear performance of a ceramic. However, the mechanisms of tribochemical interaction remain unclear. This paper presents a detailed study of the wear of zirconia toughened ceramics against metal and ceramic counterfaces in the regime that the above mechanisms would be expected to operate. No evidence of surface plasticity or microfracture was obtained. The surface contact was found to be largely elastic with minimal transformation of the tetragonal to monoclinic phase. The dominant wear mechanism was tribochemical as a result of dissolution of the ceramic surface into a metallic oxide transfer film for the metal counterface, and the formation of an amorphous surface hydrate against a ceramic counterface. In both instances, it is considered that the tribochemical reaction dictates the minimum wear rate achievable and therefore particular attention should be paid to modification of the ceramic composition to optimise the surface chemistry to promote the optimum hydrate properties.