Recent Development of Porous Materials Deposits and Structured Surface by Spray Deposition of Surface-Melted Particles

Thermal spray coatings are generally deposited by a stream of sufficiently melted particles on a roughened substrate surface. The spreading of melted spray particle fraction along substrate surface leads to the filling of melt into cavities exposed on coating surface and the formation of a dense coating. The porosity level in a thermal spray coating is limited up to about 20% down to less than 1%. The inclusion of nonmelted particles in the coating may increase porosity in the coating. However, high velocity impact of spray particles tends to cause rebounding of solid core off substrate. Recently, an effective deposition method was developed for semi-melted spray particles by controlling coating surface temperature. In this article, the recent advances on the deposition of porous materials and ceramic abradable coatings by surface-melted spray particles are reviewed. The key issues for successive deposition of porous deposits are addressed. The bonding formation between particles by controlling deposit surface temperature is essential to construct porous deposits. By using flame spraying, different metallic porous deposits up to tens of millimeter thick from refractory Mo to stainless steel are fabricated of a porosity level of up to 70%. Porous Al2O3 and YSZ of a porosity of over 60% are deposited for high temperature abradable coating applications directly by semi-melted ceramic particles. The deposition of convex-shaped YSZ particles is employed to construct the high performance structured cathode for solid oxide fuel cell application. Moreover, the deposited convex-shape particles are also utilized to fabricate effective super-hydrophobic surface. The recent progresses on the deposition of surface-melted spray particles extend many new application fields for thermal spraying.