Effects of silicon carbide in semi-metallic brake materials on friction performance and friction layer formation

The research presented in this paper is focused on the effect of silicon carbide (SiC) on friction-wear properties of semi-metallic friction composites (FC). Semi-metallic FC with increasing content of silicon carbide (SiC: 0, 3.4, 5.6, 9 and 14.6 vol.%) were prepared and slid against cast iron disc and their friction-wear properties were evaluated. The friction coefficient (μ) was observed to increase with SiC content, nonetheless the highest content (14.6 vol.% of SiC) did not significantly increase its value. The volume wear rate (V) of tested friction composites slightly increases with SiC content and temperature. The character of friction layer was analyzed using scanning electron microscopy (SEM) with energy dispersive X-ray microanalysis (EDX) and the topography of friction surface was studied using atomic force microscopy (AFM). Two types of films assigned as film I and film II appearing on the friction surfaces of samples after friction test were observed. Film I originate on the friction surface of sample without SiC and is composed of debris of iron, iron oxide, stibnite and carbon. Film II is formed on the friction surface of composites containing SiC and in contrast to film I contain additional debris of SiC.