Microstructure and properties of thermally sprayed silicon nitride-based coatings
The preparation of thermally sprayed, dense, Si3N4-based coatings can be accomplished using composite spray powders with Si3N4 embedded in a complex oxide binder matrix. Powders with excellent processability were developed and produced by agglomeration (spray drying) and sintering. Optimization of the heat transfer into the powder particles was found to be the most decisive factor necessary for the prodn. of dense and well-adhering coatings. In the present work, different thermal spray processes such as detonation gun spraying, atm. plasma spraying with axial powder injection, and high-velocity oxyfuel spraying were used. The coatings were characterized using optical and SEM, XRD, and microhardness testing. The wear resistance was tested using a rubber wheel abrasion wear test (ASTM G65). In addn., thermoshock and corrosion resistances were detd. The microstructure and the performance of the best coatings were found to be sufficient, suggesting the tech. Applicability of this new type of coating.