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

In this paper, composite powders of Al/Fe2O3 were fabricated by mechanical glomeration with micron-sized Al and Fe2O3 powders, then the composite powders were sent into plasma flame. According to the self-propagation high-temperature synthesis theory, the reduce reaction between the component after a short while heating. When the flying droplets impacting the substrate, the composite coating can be obtained with the thickness of 500 m . The microstructure, microhardness, fracture toughness and wear resistance of the coating were tested. Meanwhile, the reaction mechanics was studied.The effect of dispersant agent, bonder and the drying temperature on the physical property of the composite was studied systematically. It shows that ideal composite powders can be obtained with the process variable as following: the selections of dispersant agent and bonder are alcohol and PVA respectively, the drying temperatures of dispersant agent and bonder are 100℃ and 50℃ respectively.The SEM and XRD results show that the coating composes of lamellar FeAl2O4, Al2O3 ceramic frame and dispersed phase of spherical Fe. The TEM results show that the skeleton of the coating is equiaxial nanosized ceramic phase (FeAl2O4), the dispersed phase is nanosized spherical metal Fe and Al2O3 phase.The fracture toughness of the composite coatings was measured qualitatively through the calculation of the crack extension force (Gc) by means of Vicer indentation technology. It shows that the fracture toughness of the nanosized composite coating is almost 2.5 times of the conventional Al2O3 coatings.Under the dry sliding wear condition, especially with high loading, the wear resistance of the composite coating is much higher than conventional Al2O3 coatings. The adhesive wear and grinding abrasion play an important role with lower loading. With the increasing of loading, the grinding wear is the main abrasion mechanism with the worn surface coated with more ferric oxide, which can serve as self-lubricating film to decrease the wear rate and friction coefficient.The reaction mechanism and reaction model were obtained. It shows that the reaction of the synthesis proceeds by steps, the atomization of the plasma flame and cooldown rate provide the synthesis of nanosized coating with advantage condition.