Fabrication of Aluminum Nitride Coating onto metal substrate by Reactive RF Plasma Spraying

Aluminum nitride (AlN) is one of the attractive ceramics in respect of its excellent properties. It was possible to fabricate Al/AlN composite coatings onto carbon steel substrate by reactive RF plasma spray process. However, most of the coatings peeled off due to the difference of thermal expansion coefficient between AlN and carbon steel. It might be possible to prevent peeling of AlN coatings with formation of Al layer between substrate and AlN coating. To fabricate these coatings, it was necessary to control the nitriding reaction. Thus, nitriding process of aluminum powder in the reactive RF plasma spray process was investigated. Then the coatings were fabricated with changing nitrogen flow rate in the plasma gas. Although it was difficult to fabricate functionally graded AlN coating, it was possible to prevent the peeling off of the coatings with formation of Al layer between carbon steel substrate and AlN layer on the surface of the coatings.