Mechanical behavior of PACVD TiC–amorphous carbon composite layers

Hard composite layers consisting of TiC and amorphous carbon have been prepared by plasma-assisted chemical vapour deposition. It could be shown by high-resolution transmission electron microscopy (TEM) that nanocrystalline TiC particles are embedded in a matrix of amorphous carbon. Further TEM investigations revealed the occurrence of cracks in regular distances of approximately 400 nm. The stress state of TiC, amorphous carbon (a-C) and TiC/a-C layers was determined by the measurement of the substrate curvature in dependence on the layer thickness. High compressive stress was found for the TiC layers independent of the layer thickness, whereas a-C layers yielded only a low compressive stress. The stress difference of the two components is the reason for crack formation in the composite layers leading to a stress relaxation increasing with the layer thickness. Sliding tests with layers of compositions corresponding to the maximum hardness demonstrated a sliding and abrasive wear behavior comparable to that of PVD metal containing diamond-like carbon.