Crack propagation in nitrogen-implanted glassy carbon observed during scratch testing

Abstract

The purpose of this work was to study the mechanism of crack propagation under friction and wear of glassy carbon (GC) in the virgin state and when implanted with a high dose of nitrogen. The experiments were carried out on a scratch tester with a diamond Vickers indenter and with 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 (humidity ∼50%). Mechanisms of crack propagation in brittle materials, such as GC were considered on the atomic-molecular and the macroscale 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 indenter and with a steel ball when high loads were applied. A characteristic load, P*, of the transition from the inherent natural flaws to the Hertzian ring/cone cracks was estimated. The formation of this debris along the wear track is shown to be due to the extension of lateral vent cracks. Subsequently, larger wear particles are developed.