Fabrication of porous stainless steel through semi-molten spray particles deposition by flame spraying

Porous materials possess many unique properties. Many processes have been employed to fabricate porous materials. Recently, it was found that a porous deposit can be created through controlling the deposition of semi-molten spray powder particles. In this study, porous 316L stainless steel deposits were prepared by flame spraying under different spray conditions to aim at controlling deposit porosity. During deposition the temperature of the substrate or/and deposit surface was kept at 600°C to ensure bonding formation between the spray particle and underlying particle. To understand the deposition process mechanism, the velocity of spray particles was quantitatively measured and the morphology of deposited isolated particles was characterized by scanning electron microscopy to estimate the melting degree of spray particles before impact. The microstructure of porous 316L stainless steel deposits was characterized by scanning electron microscopy and deposit porosity was estimated from its cross section by image analysis. It was found that pores were uniformly distributed in the deposit. The results showed that porosity of the 316L deposits changed from 20% to 50% with the change of spray particle melting degrees, resulting from the change of spray parameters. The examination showed that 3D through-deposit pore-net structure was created by viscoplastic flowing of the molten fraction of semi-molten particles which forms the bonding between necks of particles. The present results clearly demonstrated that a porous ferrous alloy based material can be formed by spray deposition through controlling the melting degree of spray particles.