Controllable Preparation Of Al/Fe/Fe₂O₃ Double-Coated Powder And Its Composite Coating Performance

Al/Fe/Fe2O3 composite powders,which were the double-coated core-shell structure,were prepared by the electroless plating combined with precipitation method.The influence of various reaction parameters on the coating effect of Fe2O3 during the preparation process of composite powders were explored.The optimum technological parameters were determined,and the composition,microstructure and thermal properties of Al/Fe/Fe2O3 composite powders were also analyzed.The composite powders were applied to the preparation of composite coatings by reactive plasma spraying,and the phase composition,microstructure and properties of the composite coatings were tested and analyzed.The parameters of Al/Fe/Fe2O3 composite powders with double-coated core-shell structure prepared by electroless plating combined with precipitation method are obtained:when the concentration of Fe2+ is 0.20 mol/L,the concentration of ammonia is 1.20 mol/L,the reaction temperature is 45?C,the reaction time is 60min and add 1.25g PEG 1500 additive,the coating effect of the Al/Fe/Fe2O3 composite powder obtained after calcination at 500? for 2h is the best.The average mass fraction of iron oxide is 27.50%,and the average coating rate of iron oxide reached 56.44%.Observing the morphology of the composite powder,it was found that the Fe was coated on the surface of the A1 powder in a net shape.The reticulated Fe was formed by the aggregation of many pyramidal particles,and the thickness of the Fe shell layer was about 4?m.The Fe2O3 was deposited on the surface of the Al/Fe powder in the form of nano-sized short rod and the Fe2O3 coating is thick and relatively uniform,which realized double-layer coating of Al powder.The DSC analysis of the Al/Fe/Fe2O3 composite powder shows that the exothermic peak of the aluminothermic reaction of A1 and Fe2O3 appears at 1055?,and the exothermic enthalpy of the reaction is about 913J/g.The addition of Fe affected the aluminothermic reaction of A1 and Fe2O3,and to a certain extent,it can reduce the aluminothermic reaction temperature of Al and Fe2O3.Using Al2O3 powder,Al/Fe composite powder and Al/Fe/Fe2O3 composite powder as spraying powder,single-layer coatings and double-layer coatings(Al2O3 coating,Al/Fe coating,Al/Fe/Fe2O3 coating,Al/Fe+A1203 coating,Al/Fe/Fe2O3+Al2O3 coating)were prepared on the Q235 steel by reactive plasma spraying.The microstructure and composition of coatings were studied by SEM,EDS and XRD,and the bonding strength,hardness,thermal shock resistance,porosity and corrosion resistance of coatings were also tested.The results showed that the main phases of Al/Fe coating were Al2O3,Al,Fe3Al and FeO,and the main phases of Al/Fe/Fe2O3 coating were FeAl2O4,Fe3Al,Al2O3,Al and FeO.Both coatings have the Fe3Al intermetallic compounds,indicating that both composite powders can be used as the transition layer between Al2O3 coating and the stell substrate.By analyzing the thermal shock resistance and bonding strength of different coatings,it can be concluded that the thermal shock resistance and bonding strength of the composite coating are higher than the performance of Al2O3 coating.The transition layer which made by self-made powder can reduce the thermal performance difference between the Al2O3 coating and the steel substrate,and improve the performance of the coating.The composite coating prepared with the Al/Fe/Fe2O3 composite powder as the transition layer(Al/Fe/Fe2O3+Al2O3 coating)has the best performance,the times of thermal cycling can reach 25 times under 15-750?,the bonding strength is 24.27 MPa,the porosity of the coating is 7.6%and the corrosion resistance is well.