Abstract
Decomposition of the nitride ceramic particles like aluminium nitride (AlN) during conventional thermal spray process prevents their deposition on the substrate. Reactive plasma spraying (RPS) is a promising solution to fabricate AlN coatings. It is based on reaction and deposition of molten particles in active nitrogen ambient to form the AlN phase. Several thick AlN based coatings were fabricate successfully by reactive plasma spraying of aluminium and/or alumina particles. This study shows our recent achievements of fabrication of AlN coatings with improved conductivity. It was possible to fabricate AlN based coatings through reactive spraying of fine alumina particles mixed with fine AlN additives. Using small particle size powders improved the particles melting, surface area, therefore nitriding conversion and the AlN content. The fabricated AlN based coating contains several of oxide phases, with low density and high porosity, therefore its thermal conductivity was very low (about 2.6 W/m.K). To fabricate AlN coatings with high thermal conductivity, a liquid phase promoting additive (yttria) was added to the feedstock powder. It assists the formation of the yttrium aluminate (Y-Al-O) phase and therefore the sintering of the coatings during heat treatment. Finally, AlN coating with improved thermal conductivity (above 90 W/m.K) was developed.
