Recent development of porous materials and structured surface fabrication by spray deposition of surface-molten particles

Thermal spray processes are generally employed to deposit dense coatings. The porosity in a thermal spray coating is limited up to about 20% down to less than 1%. The porous abradable coatings can be deposited by using composite powders containing pore-forms such as polymer. Recently, an effective method to deposit porous coating are being developed by directly utilizing semi-melted spray particles through controlling coating surface temperature. In this article, the recent investigations on the deposition of porous materials and ceramic abradable coatings by surface-melted spray particles are reviewed. The bonding formation between particles by controlling deposit surface temperature is essential to form porous deposits. By using flame spraying, different metallic porous deposits up to tens of millimeter thick from refractory molybdenum (Mo) to stainless steel are fabricated with a porosity level up to 70%. Porous alumina (Al₂O₃) and yttria-stabilized zirconia (YSZ) with a porosity of over 60% are deposited for high temperature abradable coating applications directly by semi-molten 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 will extend many new applications for thermal spraying.