Coating hardness effect on the critical number of friction cycles for wear particle generation in carbon nitride coatings

Abstract

Wear particle generation in carbon nitride coatings by a spherical diamond counterpart in repeated sliding contacts has been studied with an emphasis on the effect of coating hardness, through varying two nitrogen incorporation conditions of ion acceleration energy (I.A.E.) and ion current density (I.C.D.). With a pin-on-disk type apparatus installed in the chamber of an environmental scanning electron microscope (E-SEM), the motivation of this paper is to show the direct evidence of when and where the wear particles of non-conductive carbon nitride coatings deposited onto silicon substrates do generate under controllable relative humidity, rather than infer that how wear particle generation do occur from post-testing observation. Based on the in situ examination, the shape transition maps for generated wear particles have been obtained for various nitrogen incorporation conditions. The results show that the critical number of friction cycles, Nc, for detecting a cluster of wear particles is observed to be generally decreasing with an increase in both ion acceleration energy and ion current density. However, the effect of ion acceleration energy seems to be somewhat bigger than that of ion current density, not only on the critical number of friction cycles, Nc, but also on the coating characteristics, such as surface roughness, nano-indentation hardness and internal stress. It is found further that the critical number of friction cycles, Nc, is showing a linearly increasing behavior with an increase in nano-indentation hardness, which is determined by both ion acceleration energy and ion current density during an ion beam assisted deposition process.