Direct Spraying of Fine Ceramic Particles in Thermal Spray

Deposition of ceramic coatings by spraying of fine powder particles is a promising solution to obtain uniform microstructure and improved properties, because it is expected to form small splats with reduced residual stress and pore size. Although direct injection of fine particles has many challenges such as poor rheological properties (e.g., low flow ability and agglomeration), and small momentum to inject and impact, it is still attractive and worth to try. From this point of view, we have improved feeding and injection technique of fine powder particles, which enables us to directly spray fine ceramic particles with a newly developed low power dc plasma torch. Preliminary results obtained with this system will be compared with those by other fine powder spray technology such as suspension plasma spray and hybrid aerosol deposition to show similarity and difference when the injection methods of the fine powder particles are different in this paper.