Fabrication of Porous Stainless Steel Through Semi-Melted Spray Particles Deposition by Flame Spraying

Porous materials possess many unique properties. Many processes have been employed to fabricate the porous materials. Recently, it was found that through controlled deposition of semi-melted spray powder particles a porous deposit can be created. In this study, porous 316L stainless steel deposits were prepared by flame spraying under different spray conditions to aim at controlling the porosity of the deposit. During deposition the temperature of substrate or/and deposit surface was kept at 600°C to ensure the bonding formation between spray particle and underlying particle. To understand deposition process mechanism, the velocity of spray particles was quantitatively measured and the morphology of deposited isolating particles was characterized by 3D laser 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 analyzing. The phase composition was examined by x-ray diffraction. It was found that pores were uniformly distributed in the deposit. The results showed that porosity of the 316L deposits changed from 30% to 60% 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 melting fraction of semi-melted 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 by controlling the melting degree of 316L stainless steel particles.