Investigations on Thermal Spraying of Silicon Nitride-Based Powders

Abstract

Thermal spraying of silicon nitride has been considered impossible because the high temperatures of the spray processes lead to its decomposition and oxidation. To suppress the degradation oxide bonded silicon nitride spray powders (OBSN) have been developed. In this paper spray experiments with these powders by detonation gun spraying (DGS) and atmospheric plasma spraying (APS) with axial powder injection are described. All coatings were characterized using optical microscopy and X-ray diffraction. In addition, DGS coatings were also investigated using SEM, microhardness testing and a rubber wheel abrasion wear test. For the first time, relatively dense Si3N4-rich coatings with an oxide binder phase were produced. The abrasion wear resistance of some DGS coatings was found to be sufficiently high to envisage industrial application. Further progress is expected from optimized spray experiments with variations of spray powder composition and particle size.

Silicon Nitride Ceramics: Structure, Synthesis, Properties, and Biomedical Applications

“…The plasma at the arc initiating point then receives an electromagnetic force pulse and forms an electromagnetically accelerated plasma of the working gas that heats and propels the powder particles with supersonic speed towards the substrate (Figure 3d,e). adhering coatings with high silicon nitride contents [46,47]. In addition, the optimization of heat transfer into powder particles to control the critical viscosity of the oxide binder phase was found to be one of the most decisive factors [48] that requires sophisticated powder preparation procedures [49].…”

“…The coating consists prominently of α-Si3N4, minor amounts of ß-Si3N4, and traces of YAG and SiAlONs with different degrees of substitution 1 < z < 4, predominately z = 1. The powders used for detonation and EMAP spraying were synthesized by mixing commercial α-Si3N4 powder with oxidic sintering aids such as alumina and yttria, agglomerated by spray drying using an organic binder and subsequently sintered at 1450 • C in a nitrogen atmosphere [46,51]. The powders used for detonation (Figure 4A) and EMAP spraying (Figure 4B) contained 68 mass% Si3N4 + 16 mass% Al2O3 + 16 mass%, whereby the volume of the oxidic binder phase comprised 30%.…”

“…However, later it was recognized that high particle velocities generated by detonation spraying, Top Gun™ technology, high-frequency pulse detonation, or atmospheric plasma spraying with axial powder injection were essential to deposit dense and well-adhering coatings with high silicon nitride contents [ 46 , 47 ]. In addition, the optimization of heat transfer into powder particles to control the critical viscosity of the oxide binder phase was found to be one of the most decisive factors [ 48 ] that requires sophisticated powder preparation procedures [ 49 ].…”

“…The powders used for detonation ( Figure 4 A) and EMAP spraying ( Figure 4 B) contained 68 mass% Si3N4 + 16 mass% Al2O3 + 16 mass%, whereby the volume of the oxidic binder phase comprised 30%. The approximate composition of the resulting SiAlON binder phase was found to be Si 3 Al 3 O 3 N 5 (z = 3) [ 46 ] and Si 5 AlON 7 (z = 1) [ 51 ] for detonation- and EMAP-sprayed coatings, respectively.…”

Processing and properties of plasma sprayed silicon nitride-glass composite coatings

“…Further efforts to improve the coating quality were made using detonation gun spraying and axial powder injection atmospheric plasma spraying, but the decomposition of the silicon nitride phase presented another problem. 9 Research has been reported on spraying a mixed powder of silicon nitride with crushed soda-lime glass but again the quality of the coating microstructure and properties were limited. 10 This research will use a low temperature borosilicate glass as a binder to produce silicon nitride-glass composite as feedstock for thermal spraying.…”