Fabrication of AlN Coatings by Reactive Atmospheric Plasma Spray Nitriding of Al Powders

Abstract

Atmospheric Plasma Spray (APS) is well-established process and is widely used to produce various coatings with high deposition rate for structural and functional applications. Aluminum nitride is a promising material due to its outstanding properties. In this study, AlN coatings were synthesized by APS process through reactive plasma nitriding of Al powders by nitrogen plasma. Al powders were supplied into the plasma stream by Ar carrier gas and reacted with the surrounding plasma, then were deposited onto substrate. The obtained coatings were cubic-AlN/Al mixture with 100 μm of thickness at 150 mm of spray distance. Since the nitride content increases gradually with spray distance, the coating almost consists of AlN at 300 mm. However, the thickness of the coatings decreased with increasing spray distance, it was less than 10 μm at 300 mm spray distance. The nitriding reaction was investigated and it indicated that Al particles may react during flight and after deposition on the substrate surface. Completing the nitriding during flight (formation of AlN in-flight) decreases the coatings thickness. We can conclude that enhancing the nitriding reaction after deposition at short spray distance may enable to fabricate thick AlN based coatings.