TRANSITIONS OF MICROSCOPIC WEAR MECHANISM FOR CR2O3 CERAMIC COATINGS DURING REPEATED SLIDING OBSERVED IN A SCANNING ELECTRON-MICROSCOPE TRIBOSYSTEM

The purpose of this investigation is to analyse microscopic wear modes and their transitions for Cr2O3 coatings in repeated sliding. For this purpose the wear processes during 100 sliding cycles were observed successively in a scanning electron microscope tribosystem. They were also compared with those of a metal, SUS304 stainless steel. The type of wear test was pin on disc. Cr2O3 coatings on SUS304 stainless steel were used for the disc specimens. The thickness of the coatings was 400-mu-m. The pin specimen was made of single-crystal diamond with a hemispherical tip of radius 30-mu-m. The sliding velocity was 400-mu-m s-1. The normal load was changed from 0.07 to 1.5 N. The following results were obtained. (1) The wear modes are classified into crack and powder formation, flake formation and ploughing and powder formation. These wear modes are mainly caused by surface crack propagation. (2) The wear modes change during repeated sliding as follows for loads from 0.2 to 1.5 N: crack and powder formation (low wear rate)-flake formation (high wear rate) --> ploughing and powder formation (negligible wear rate). When W = 0.07 N, the wear mode is ploughing and powder formation and there is no transition to other wear modes. (3) The condition for wear mode transition can be explained theoretically by using the parameter of severity of contact, S(c), and the friction coefficient-mu, where S(c) = P(max) (R(max))1/2/K(Ic).