Thermally sprayed silicon nitride-based coatings on steel for application in severe operation environments. Preliminary results

Thermal spraying of pure silicon nitride has been considered impossible because the high temperature involved causes the material to decompose and oxidize. To suppress the thermal degradation, oxide-bonded silicon-nitride (OBSN) spray powders have been developed. In this contribution thermal spray processing of such powders by APS with axial powder injection, and DGS will be described. Spray powders and coatings produced from them were characterized using optical microscopy, X-ray diffraction, and SEM. In addition, some mechanical properties of DGS coatings were also investigated using microhardness indentation testing and a rubber wheel abrasion wear test. Very dense, well adhering Si3N4-rich coatings were produced containing a mixed oxide binder phase. The abrasion wear resistance of some DGS coatings was found to be sufficiently high to suggest technical application in areas subjected to harsh environmental conditions.