Influence of Transient Liquid Phase Promoting Additives upon Reactive Plasma Spraying of AlN Coatings and Its Properties

Abstract

and YAG) are fabricated. Fine Y 2 O 3 acts as transient liquid phase promoting additive, and reacts with Al 2 O 3 phase (from feedstock mixture and on AlN particles surface) to create wetting agent of yttrium aluminate Y-Al-O around solid AlN particles. However, due to rapid solidification rates of plasma, it is difficult to react with the interspersed oxygen in AlN grains. The Y 2 O 3 addition significantly reduces the coatings oxide content due to the consumption of starting Al 2 O 3 to form the YAG. Influence of Y 2 O 3 significantly observes with increasing AlN feedstock and high AlN content coatings with small oxides are fabricated by RPS of 80AlN-10Al 2 O 3 -10Y 2 O 3 mixture. Thermal conductivity is improved with using Y 2 O 3 and increasing AlN feedstock. However, the conductivity is not so high compared to the AlN compacts, due to increased porosity, incomplete sintering of the formed initial liquid phase state, remaining oxide content, and low density of the coatings.

Synthesis of Cubic Aluminum Nitride (AlN) Coatings through Suspension Plasma Spray (SPS) Technology

“…However, sometimes it is not necessary to melt the particles fully, because it is possible for particles in a semi molten state to be deposited as a coating. Moreover, a thermal plasma process can allow for a wide range of coating thicknesses, stretching from nm to mm [41]. In order for the deposited coating to stick to the substrate, the injected particles must melt or be in semi-molten state when they pass through the hot core of the plasma.…”

“…In order for the deposited coating to stick to the substrate, the injected particles must melt or be in semi-molten state when they pass through the hot core of the plasma. The high melting point of AlN (2200 • C) as well as its decomposition at high temperatures does not facilitate the deposition of AlN particles injected through the plasma [41].…”

“…Melamine (C 3 H 6 N 6 ), an organic compound containing about 67 wt% nitrogen is a trimer of cyanamide, with a 1,3,5-triazine skeleton, that releases nitrogen at high temperatures [46], and has been used to produce AlN powder by mechanochemical reaction with Al [47]. Direct injection of nitriding powders such as urea or melamine with Al into plasma, unlike N 2 gas, is challenging, particularly when there are different precursor components with various particle sizes and densities [41].…”

Microstructure, Thermal and Mechanical Properties of AlN-MgO Composites Prepared by Spark Plasma Sintering

“…Recently, various surface techniques, such as physical vapor deposition (PVD) and plasma spraying [10][11][12], have emerged for the facile fabrication of AlN thin films.…”