| Effects of air plasma spraying parameters on the formation of the icosahedral quasicrystalline coatings onto a mild steel plate were investigated using gas atomized Al_(62)Cu_(26)Fe_(12) powders. The as-atomized powders were appropriately sieved to have a size range of-200∼+400 mesh. Heat treatment at 750℃ for 3 hours was carried out to investigate the phase stability of the powders. Main process parameters such as arc current, spraying distance, powder feeding rate, preheating of the substrate were correlated to the coating layer characteristics. The volume fraction of the quasicrystalline phase in the coating layer was found to be a function of the chemistry and solidification history of the splats. Due to excessive evaporation of Al atoms during spraying, an initial powder composition more or less changed to form the β-AlFe(Cu) phase. As the arc current increased from 300 A to 500 A, both surface hardness and cross sectional hardness increased. The coating thickness was found to be a function of arc current, powder feeding rate, but less influenced by the spraying distance. The porosity level increased with an increase of arc current, spraying distance, and powder feeding rate. It is suggested that the atmospheric plasma coating process has a potential possibility of obtaining quasicrystalline coating layer, provided that the processing parameters are effectively optimized for obtaining high quantity of quasicrystalline phase. |
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