EFFECT OF THE PECVD-A-SIC TOP COATING ON THE PASSIVATION RESISTANCE OF TITANIUM-NITRIDE-COATED STEEL IN 3.5-PERCENT NACL SOLUTION

An attempt was made to use plasma-enhanced chemical vapor deposited a-SiC as a top coating on titanium-nitride-coated steel to improve its corrosion resistance in NaCl solution. The coating parameters were varied in order to reveal the effect on passivation resistance. The experimental results showed that a transparent a-SiC film can be obtained without changing the color of the titanium-nitride-coated specimen. The film thickness and microstructure of the a-SiC coating changed depending on the coating parameters, and the subsequent passivation resistance also changed. In addition to film thickness, the nodular structure in the a-SiC film due to radical-molecule reactions was found to be responsible for good corrosion resistance when the r.f. power was varied. Maximum passivation resistance was found for moderate substrate temperatures. This is suggested to be the consequence of the poor quality of a-SiC film deposited at low temperatures and the thermal failure between film and substrate at high temperatures.