Effect of carbon interlayer on protective properties of hydroxyapatite coating deposited on 316L stainless steel by sol-gel method

Good-quality bilayer coatings with a carbon interlayer and outer carbonate hydroxyapatite layer are obtained on AISI 316L stainless steel substrate using RF PACVD and sol-gel methods. It is found that protective properties of both composite C/HAP coating and HAP coating depend on the temperature of heat treatment. Hydroxyapatite with a carbon interlayer coating annealed at 500°C significantly improves corrosion resistance of the stainless-steel substrate as well as of unary carbon and HAP coatings. The composite C/HAP coating annealed at 500°C exhibits better corrosion resistance in comparison with the HAP coating heated at the same temperature. Stainless-steel substrates with a HAP and C interlayer heated at 700°C have worse corrosion features in comparison with uncoated AISI 316L. The weak corrosion resistance of this sample is due to the formation of metal carbides at this temperature.