Comparison between single and multilayered a-SiC:H coatings prepared by multi-frequency PACVD: Mechanical properties

Due to their low density and good mechanical properties, titanium alloys are commonly used to lighten structures in aeronautical applications. Unfortunately, their friction properties are poor due to titanium oxide layers which naturally occur. To confer to the surface both high mechanical resistance under load and low friction/low wear against other metals, amorphous silicon carbide (a-SiC:H) coatings are deposited on plasma treated substrates, using a multi-frequency plasma CVD device. The present study is devoted to compare scratch properties of single and multilayered a-SiC:H layers including up to 125 asymmetric periods of soft/hard coatings. Standard scratch-testing measurements reveals that the critical load corresponding to the formation of cohesive/adhesive cracks can be significantly increased (by a factor of 2.5) when using multilayered coatings. When optimized coatings are deposited, the substrate is not visible at the bottom of the flaked area until loads higher than 60 N are applied.