Preparation Of Fe₂O₃/Al Composite Powders And Its Application In Fe-Al/Al₂O₃Composite Ceramic Coating

In this paper, Fe₂O₃/Al composite powders were prepared by homogeneous precipitation method, and the Fe-Al/Al₂O₃ composite coating was prepared by reactive plasma spraying technology with Fe₂O₃/Al composite powders. The influence of various factors on the coating effect of the composite powder was explored, and the optimum parameters were determined. The composite powders were analyzed by means of XRD, SEM, TEM, EDS, FTIR, DTA and so on. According to the Self-ropagating High Temperature Synthesis reaction, the composite powders were fed into the plasma flame flow to react, and the composite ceramic coating is formed and deposited on the steel substrate, the micro structure, composition structure and thermal shock resistance of the coating were analyzed, and the thermodynamic reaction and formation mechanism during the spraying process were also studied.By studying the influence factors on the coating effect of Fe₂O₃/Al composite powder, including the concentration of ferrous ion, the molar ratio of raw materials, reaction temperature, reaction time and the particle size of aluminum powder, it can be known that when the concentration of ferrous ion is 0.2mol/L, the molar ratio of urea to ferrous sulfate is 20:1, the reaction temperature is 80℃, reaction time is 180min, the coating effect of the prepared composite powders is the best. The percentage coating of the composite powder was 14.1%, and the coating efficiency reached more than 77%.XRD results show that before calcination, the surface of the aluminum powder was coated with a layer of α-FeOOH, and became α-Fe₂O₃ after calcination; SEM and TEM results show that iron oxide prepared by homogeneous precipitation method was nano rod and cluster structure coated on the surface of the aluminum powder, iron coated layer is thick and dense, the thickness is about 2 μm; FTIR results show the presence of Fe-O bond on the surface of the composite powder; DTA test results show that the reaction of the composite powder released a lot heat at about 1000 degrees, which proves the feasibility of using the composite powder for reactive plasma spraying.Self-made powders spraying coating, alumina ceramic coating and alumina/self-made powder spraying composite coating three kinds of coatings were prepared by reactive plasma spraying technologyFe₂O₃/Al composite powders and alumina powders. Through the XRD test, it can be found that there are mainly four kinds phase in the coating, including:Al, FeAl₂O4, Fe₃Al and γ-Al₂O₃.The existence of Fe₃Al intermetallic compound shows that it is feasible to use composite powders to prepare Fe-Al/Al₂O₃ composite coating. The presence of the hercynite indicates that the coating formation process is not the thermite reaction under equilibrium condition, but a variety of reactions coexist.By the SEM observation of the three kinds of coating, the surface structure of the self-made powders spraying coating is loose, and the porosity is large. When a layer of alumina powder is sprayed on the surface, the surface becomes denser and more uniform. The cross section morphology analysis of the three kinds of coatings shows that the self-made powder spraying coating have a good transition with the substrate, there are holes and cracks in the coating, and there is a significant component abrupt change between the alumina coating and the substrate.By the thermal shock experiment of three kinds of coatings, it can be known that the thermal shock resistance of alumina/self-made powder spraying composite coating is the best, and the thermal shock failure time is 25.The results of thermodynamic calculation and reaction mechanism study of the reaction spraying process show that the Fe₂O₃/Al composite powder has the possibility of self-reaction. In spraying process, the thermal state and the reaction degree of the reactants are different, which ultimately lead to the diversity of the phase in the coating.