Study On The FeAl₂O₄-Al₂O₃-Fe Composite Coating Fabricated By Reactive Plasma Spraying

In this paper, composite powders of Al/Fe₂O₃ were fabricated by mechanical glomeration with Al and Fe₂O₃ powders, the composite coating can be obtained with part nanophase structure by reactive plasma spraying. The micro-pattern, microstructure, fracture toughness property and wear resistance of the coating were tested and analyzed. Meanwhile, the reaction mechanics was studied.Fe₂O₃-Al composite powders were prepared using iron oxide (Fe₂O₃) powders and aluminum powders by mechanical agglomeration technique. After being mixed in a ratio and agglomerated and sieved, the Al and Fe₂O₃ powders were made into composite powders for plasma spraying, with excellent liquidity, narrow distribution and well-regularity.The composite powders were fired and reacted when they were sent into plasma flame, the molten reactants, with the help of the high-speed plasma flame, impacted with the substrate to form this composite coating. SEM and XRD were carried out to determine the microstructure composition. Experiment results showed that the composite coating consisted of stratified matrix phase FeAl₂O₄ and phase Y-Al₂O₃, and spherical phase a-Fe was dispersedly embedded in the interlamination coatings. TEM analyses indicated that FeAl₂O₄ phase was composed of equiaxed crystals and layered crystal mainly, whilst γ-Al₂O₃ and a-Fe phases were composed of spherical crystals, which were nano-scaled partially.Comparisons were made between the composite coating and conventional Al₂O₃ coating on indentation and fracture to compare their tough properties. Indentation of the composite coating was more distinct, without collapsed and buckle structures, which were found around the indention of Al₂O₃ coating. In addition, some gliding fracture properties such as fluctuations and distinct pull-out mechanism were noticed on the composite coating fracture, while Al₂O₃ coating had brittle fracture properties only. So it was concluded that this composite coating had superior toughness, as compared with Al₂O₃ coating. These dispersed particles Fe contributed to its enhanced toughness.The composite coating had enough bond strength, which was almost 1.25 times of AT13 ceramic coating with Al/Ni base coating, and without base coating, the composite coating was apparently higher than AT13 ceramic coating. At same time, the porosity of AT13 ceramic coating was almost 1.5 times of the composite coating.The wear-resistance of this composite coating was much better than that of AT13 ceramiccoating under oil lubricated condition. In this paper, the abrasion mechanism was studied. Under low load, its mechanism was partial-lubricated abrasion or boundary-lubricated abrasion. However, under high load at first boundary wear was dominant. With the abrasive behaviors continuing, it turned to mixed wear even fatigue wear followed cracks initiation on the coating surface. During the whole process, these dispersed particles Fe and the lamellar structure, thin and dense enough, contributed to the enhancement of wear-resistance.Based on thermodynamics principles, DTA analyses and the conditions of reactants melt and deposited, the reaction process of the Fe2C>3-AI composite powders injected into the jet was investigated. These analyses results showed that reactions between Fe2C>3 and Al were carried out step by step and finished before the react products sputtered on the substrate in molten condition. So that this lamellar composite coating was fabricated, with the main phases(FeAl2O4 and Fe), as well as AI2O3 phases and some residue FeO phases.