Studyd On Structure Character And Crystalliztion Of The Fe/Al₂O₃/FeAl₂O₄ Composite Coating By Reactive Plasma Spraying

In this paper, composite powders of Al/Fe₂O₃ were fabricated successfully by spraygranulation with Al and Fe₂O₃ powders, the composite coating can be obtained with partnano-phase structure by reactive plasma spraying. The microstructure and phase compositionproperty were tested and analyzed. Meanwhile, the structure character and crystallization of thetheories of every phase were studied.Al/Fe₂O₃ composite powders were prepared using iron oxide (Fe₂O₃) powders andaluminum powders by spray granulation technique. After being mixed in a ratio and granulatedand sieved, the Al and Fe₂O₃ powders were made into composite powders for plasma sprayingwhich had excellent liquidity, narrow distribution and good roundness. By plasma spraying, thecomposite powders were fired and reacted when they were sent into plasma flame. With thehelp of the high-speed plasma flame, the molten reactants, impact with the substrate and formthis composite coating. The composite coating has layered structure. SEM and XRD were usedto determine the microstructure composition. The results showed that the composite coatingconsisted of stratified matrix phase of FeAl₂O₄ and phase Al₂O₃, and spherical phase of Fe wasdispersedly embedded in the interlamination coatings. the crack propagation has beensuppressed effectively in the result of the dispersion of the Fe, and the fracture toughness of thecomposite coating has been improved.SEM, EDS, XRD were used to determine the microstructure and phase composition afterthe sample was eroded. According to experimental results, we can draw the conclusion that:1. The whole system is non-equilibrium process during the plasma spraying. FeAl₂O₄ inthe composite coating appears in the form of columnar crystal and equiax crystal. Segregationin the crystallization leads the difference in the content of Fe between the center and the surfaceof the columnar crystal appearing in the bottom of the layer, and the equiax crystal is columnarcrystal between the columnar crystal and the densy area. 2. Mostly the size of the Fe phase is smaller in the composite coating, with the shape ofparticle; only a small part of Fe phase with a flat shape caused by extrusion aggregate amongthe gray or black phases. The liquid drops of some other phase mix with the Fe phase during thetime of flight and impact, which lead to the different topography in etch pit.3. There are two kinds of Al₂O₃ in the coating, the bigger spherical ones are crystallizedfrom the liquid firstly, and the smaller ones with its size in 50¹50nm are pseudoeutecticedwith the FeAl₂O₄.