The development of sputtered carbon based coatings incorporating Cr, Ti, B and N

Abstract

Sputtered carbon coatings have been reported to have excellent tribological properties (low friction coefficient and low wear rate) and, therefore, the potential to be used as hard-solid-lubricant wear-resistant coatings. Further development of the sputtered carbon-based coatings has been carried out and the inclusion of Cr, Ti, B and N to deposit composite or multilayer coatings has been studied. The deposition process was designed to deposit a 2.0 μm CrTiBCN base layer followed by a 2.0 μm CCrTiB tribological top layer using unbalanced magnetron sputtering with one chromium, one titanium di-boride, and two carbon targets with a three axis substrate rotation mechanism. The base layer was found to have a hardness of approximately 2500 HV, a critical scratch load of L c>80 N, and a friction coefficient of μ>0.4 against a WC ball in air, similar to those of conventional hard coatings (TiN for example). The tribological top layer was shown to have both high hardness (∼2200 HV) and low coefficient of friction (∼ 0.06 under a load of 80 N in pin-on-disc tests). The nitrogen gas flow rate for deposition of the base layer, and the sputtering powers on the chromium and titanium di-boride targets for the deposition of the tribological top layer were optimized to produce coatings with the best combination of hardness, low friction and low wear rate. Pin-on-disc tests in air and reciprocating wear tests in air, in water and in oil were used to determine the tribological performance of the coating. The results indicated that this new composite coating could be used as a hard, solid lubricant film for a range of mechanical applications.