Studies of the tribological and mechanical properties of laminated CrC-SiC coatings produced by r.f. and d.c. sputtering

Multilayer CrC-SiC coatings were produced by both direct current and radio frequency sputtering of Cr and Si targets in an Ar-C₂H₂ atmosphere. Coatings of constant thickness of about 4 μm, but with the number of layers varying between two and 200, were prepared and studied. Investigations of coating morphology were performed by scanning elecron microscopy (SEM), and coating composition was investigated using Glow Discharge Optical Spectroscopy (GDOS) and Auger Electron Spectroscopy (AES). Microhardness measurements, scratch adhesion, pin on disc, ASTM rubber wheel and impact wear tests were performed and the results were related to the individual layer thicknesses. It is shown that the improvement observed in hardness tests does not necessarily result in the improvement of other mechanical properties, e.g. adhesion and toughness. When two comparatively hard materials are combined in a multilayer coating, the result can be an increase in brittleness due to an absence of plastic release mechanisms for dislocation accumulation at layer boundaries. Thus, it is necessary to seek a compromise in the hardness of multilayer films in order to achieve optimal behaviour across a range of different surface contact conditions.