CRACK-PROPAGATION IN NITROGEN-IMPLANTED GLASSY-CARBON OBSERVED DURINGSCRATCH TESTING

The purpose of this work was to study the mechanism of crack propagati on under friction and wear of glassy carbon (GC) in the virgin state a nd when implanted with a high dose of nitrogen. The experiments were c arried out on a scratch tester with a diamond Vickers indenter and wit h a steel ball. A sliding velocity of V = 0.2 mm s(-1), and loads From 0.5 to 4 N, during 50-300 cycles were applied in laboratory air (humi dity similar to 50%). Mechanisms of crack propagation in brittle mater ials, such as GC were considered on the atomic-molecular and the macro scale levels. The pre-existing flaws are likely to be responsible for the tear formation on the atomic-molecular scale. Hertzian ring cracks were observed under friction and wear of GC caused with a diamond ind enter and with a steel ball when high loads were applied. A characteri stic load, P, of the transition from the inherent natural flaws to th e Hertzian ring/cone cracks was estimated. The formation of this debri s along the wear track is shown to be due to the extension of lateral vent cracks. Subsequently, larger wear particles are developed. (C) 19 98 Elsevier Science S.A.