Aluminum nitride is a promising material for structural and functional applications. Cubic AlN (c-AlN) is expected to have higher thermal conductivity due to their high symmetry; however, its fabrication is difficult. In this study, c-AlN was synthesized by atmospheric plasma spray process through the reaction between Al feedstock powder and nitrogen plasma. Al powders were supplied to the plasma stream by Ar carrier gas and reacted with surrounding N 2 plasma, then deposit onto substrate. The obtained coatings were c-AlN/Al mixture at 150 mm of spray distance, and the nitride content was improved by increasing the spray distance. The coatings almost consist of c-AlN at 300 mm of spray distance. The coatings thickness decreased from 100 to 10 lm with increasing spray distance from 150 to 300 mm. Using carrier gas, N 2 enable to fabricate thick c-AlN coating with hardness 1020 Hv.
Feedstock powder characteristics (size distribution, morphology, shape, specific mass, and injection rate) are considered to be one of the key factors in controlling plasma-sprayed coatings microstructure and properties. The influence of feedstock powder characteristics to control the reaction and coatings microstructure in reactive plasma spraying process (RPS) is still unclear. This study, investigated the influence of feedstock particle size in RPS of aluminum nitride (AlN) coatings, through plasma nitriding of aluminum (Al) feedstock powders. It was possible to fabricate AlN-based coatings through plasma nitriding of all kinds of Al powders in atmospheric plasma spray (APS) process. The nitriding ratio was improved with decreasing the particle size of feedstock powder, due to improving the nitriding reaction during flight. However, decreasing the particle size of feedstock powder suppressed the coatings thickness. Due to the loss of the powder during the injection, the excessive vaporization of fine Al particles and the completing nitriding reaction of some fine Al particles during flight. The feedstock particle size directly affects on the nitriding, melting, flowability, and the vaporization behaviors of Al powders during spraying. It concluded that using smaller particle size powders is useful for improving the nitriding ratio and not suitable for fabrication thick AlN coatings in reactive plasma spray process. To fabricate thick AlN coatings through RPS, enhancing the nitriding reaction of Al powders with large particle size during spraying is required.
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 mm 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 mm 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.
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