Critical load for wear particle generation in carbon nitride coatings by single sliding against a spherical diamond

Abstract

The `critical load' for wear particle generation of carbon nitride coatings sliding against a spherical diamond under a linearly increasing load has been examined in situ in relation to different nitrogen incorporation conditions, i.e. assisted N ion acceleration energy and N ion beam current density, and different coating thickness. An environmental scanning electron microscope (E-SEM), in which a pin-on-disk tribotester was installed, has provided direct evidence in situ of when, how and where wear particle generation occurs during the sliding of carbon nitride coatings against a spherical diamond. The in-situ examination of non-conductive carbon nitride coatings are available in E-SEM free from surface charging with controllable relative humidity. The sliding tests under linearly increasing load up to 300 mN at a sliding speed of 10 μm/s have been carried out with the purpose of measuring the `critical load' for wear particle generation in a similar way to the traditional macro scratch testing. However, instead of the `critical load', the critical maximum Hertzian contact pressure P max will also be used in the following for better understanding. Based on the systematic study of seven combinations of nitrogen incorporation parameters and five kinds of thickness (0, 10, 50, 100 and 200 nm), the applicable range of P max for wear particle generation can be increased from 1.6 Y to 1.83∼1.92 Y or to 1.80∼1.89 Y, where Y is defined as the yield strength of silicon of 7 GPa, by coating carbon nitride onto silicon with changing nitrogen incorporation conditions of ion acceleration energy and ion current density, or varing coating thickness from 10 to 200 nm. It also appears that the observed wear particle generation of carbon nitride coatings was associated with a failure initiated in the silicon substrate rather than within the carbon nitride coating or at the coating–substrate interface in the light of both the empirical identification and the theoretical discussion.