Preparation Of Fe₂O₃/Fe/Al Composite Powders And Its Application In Composite Coating

Fe₂O₃/Al composite powders,which were the core-shell structure,were prepared by the chemical precipitation method,and the double coated Fe₂O₃/Fe/Al composite powders were prepared through the combination of chemical plating and chemical precipitation method.The influence of various reaction parameters on the coating effect of the core-shell composite powder during the preparation process were explored.The optimum technological parameters were determined,and the structure and composition of the composite powder were also analyzed.The self-made composite powders were applied to the preparation of composite coating by reactive plasma spraying,and the phase composition,structure and properties of the composite coating were tested and analyzed.By studying the influence parameters on the coating effect of Fe₂O₃ coated Al composite powder prepared by chemical precipitation method,it can be known that when the concentration of ferrous ion is 0.30mol/L,the molar ratio of NH4HCO3 to FeSO4 is 2.5:1,the reaction time is 50min,reaction temperature is 60℃,the size of Al powder is 200-300 mesh,the surface active agent is PEG1500,the coating effect of the composite powders is the best.After calcination at 500℃ for 2h,the coating efficiency of the Fe₂O₃/Al composite powder reached 40.35%,the mass fraction of ferric iron reached 30.22%.Through the observation of the morphology of the Fe₂O₃ prepared by chemical precipitation method,it was found that the Fe₂O₃ on the surface of the aluminum powder was spherical.Each micron spherical Fe₂O₃ was self-assembled by short rod like iron oxide,the short rod like iron oxide was 200nm.The size of the spherical Fe₂O₃ was about 4μm.By studying the influence parameters on the coating effect of Fe/Al composite powder,it was found that when the reaction temperature is 85℃,the size of Al powder is 200-300 mesh,the surface active agent is PVP,the coating effect of the Fe/Al composite powders is the best.The mass fraction of iron is 17.25%,and Fe was coated on the surface of Al powder with reticulation.Using the Fe/Al composite powder as the core,the micron spherical Fe₂O₃ coated Fe/Al composite powder was prepared by chemical precipitation method.The coating efficiency of Fe₂O₃/Fe/Al composite powder was 35.96%,the mass fraction of ferric oxide was 26.46%.The double layer coating on the surface of Al was achieved.Using Al₂O₃ powder and Fe₂O₃/Al composite powder and Fe₂O₃/Fe/Al composite powder as spraying powder,single coatings and composite coatings were prepared on the Q235 steel by reactive plasma spraying.The coating structure,composition and properties were studied by SEM,EDS and XRD,the results show that the main phase composition of the coating prepared by the Fe₂O₃/Al composite powder is FeAl2O4.This indicates that the reaction between Fe₂O₃ and Al is non equilibrium reaction in the process of plasma spraying.The main phases of the coating prepared by Fe₂O₃/Fe/Al composite powder are FeAl2O4,Fe3Al and Al₂O₃.The presence of Fe3Al indicates that the coating can used as the transition layer between ceramic coating and the metal substrate.that:The coating was stacked by particies with the lamellar structure.There are holes and micro cracks in the coating.coating.Mechanical embedmen is main combination between Al₂O₃ coating and substrate.According to the thermal shock analysis of different coating,the thermal shock resistance of the composite coating is higher than that of the single layer coating.The transition layer which made by self-made powder can reduce the thermal performance difference between the Al₂O₃ coating and the metal matrix,and improve the performance of the coating.The composite coating prepared with Fe₂O₃/Fe/Al composite powder as the transition layer has the best performance,the thermal shock failure time is 29 times,the porosity of the coating is 11.54%,the transition layer has good toughness,and the bond strength is best.