VSiC Coating with High Oxidation Resistance and Excellent Tribological Property

抄録

Vanadium carbide (VC) coating has been widely used as wear-resistant hard coating on forging dies for its high hardness and good tribological property. In recent years, oxidation resistance is also required for hard coatings in addition to hardness and tribological property, as the processing conditions become more severe such as hot stamping, stamping of high tensile strength steel and processing with poor lubrication. Therefore, applying VC coating for such high-load processing is difficult due to its low oxidation resistance. For improving its oxidation resistance, Vanadium silicon carbide (VSiC) coating was developed by adding silicon (Si), an element that imparts oxidation resistance to the VC coating.
The VSiC coatings was deposited on HSS substrate using the PECVD (Plasma Enhanced Chemical Vapor Deposition) method. The composition, structure and hardness were investigated by using EPMA (Electron Probe Micro-Analyzer), XRD (X-ray Diffraction), Raman spectroscopy and nanoindentation. The oxidation resistance was evaluated by examining the changes in chemical composition and hardness after heating in an atmospheric environment. No significant change in composition and hardness was observed even after being heated to 800℃. This result shows VSiC coating has high oxidation resistance compared with that of VC coating.
Tribological properties of the VSiC coating were evaluated using the ball-on-disk test method with S45C ball. The results showed that VSiC coatings with lower carbon content had higher friction coefficients (≒0.8) and a larger amount of adhesions within the sliding tracks. On the other hand, as the carbon content increased, the friction coefficient decreased (<0.2), and simultaneously, the amount of adhesions within the sliding tracks decreased. The results of Raman spectroscopy for samples with higher carbon content showed the presence of amorphous carbon in the coating. Consequently, it is suggested that amorphous carbon in VSiC coating contributes to suppressing formation of adhesions and attaining excellent tribological property.