| Preparation of ceramic coating on metal substrate can obtain both the strength and toughness of metal matrix and the wear-resisting and high temperature oxidation resistance of ceramic coating. But the difference of physicochemical properties of Al2O3 ceramic coating and the metal substrate lead to the poor tensile adhesive strength between coating and substrate, so the transitional layer or phase is needed. Fe-A1 intermetallic compound has been widely studied because of its special structure, high mechanical performance and cost-effective. It can be used as transitional phase between metal matrix and ceramic coatings to enhance the performance of composite coating. Although there are many methods to prepare Fe-Al intermetallic compound, but preparation of the powder is very difficult and dangerous. In this paper, composite ceramic coating was prepared with controllable secondary plating Fe/Al composite powder and Al2O3 powder via plasma spraying. Fe-Al intermetallic compound was produced via in-situ reaction of Fe/Al composite powder in the high temperature and it can be used as transition phase to enhance the coating performance.Fe/Al composite powder was prepared via electroless plating. In the plating solution, FeSO4·7H2O, C4O6H4KNa, C6H8O7, NaH2PO2·H2O were used as main salt, main complex agent, auxiliary complex agent and reducing agent, respectively. Actively treated A1 powder was used as core. Fe/Al composite powder was prepared under the conditions of water bath and stirring. Study on the experimental conditions and Al active treatment can obtain conclusions:The treatment of A1 powder has large influence on the cladding effect of composite powder. Fe/Al composite powder has less peeling and dissociative iron particles which was prepared with NaOH treatment of A1 powder. The active concentration of NaOH is 1.8 g/L. Certain iron content of composite powder can be prepared by controlling the reaction time, concentration of FeSO4 and the temperature of water bath. The optimized parameters for electroless plating were listed as follow:temperature 80℃, FeSO4·7H2O 14 g/L, reaction time 50 min. The iron content of the Fe/Al composite powder was 26.6% under the optimized parameters. In order to further improve the iron content, the secondary plating Fe/Al composite powder was prepared with HCl and NaOH comprehensive treatment of pre-prepared composite powder. The iron content can be increased to 44.2%.SC, DC, TC, GC and single Fe-Al composite coating specimens were prepared on the surface of Q235 steel via plasma spraying. The formation process of coating, porosity, residual stress and combination between matrix and ceramic coating are analyzed in theory. The microstructure and properties of the coating specimens were investigated by means of SEM, EDS, XRD, etc. The results show that:The particles in the composite coating present typical lamellar structure. There is a small amount of pores, micro cracks, oxide inclusions, un-melted particles, loose organization and other defects in the coating. Mechanical tabling is main combination between coating and substrate. Phases composition of coating are include of Fe3O4、Al、α-Al2O3、γ-Al2O3、Fe3Al, etc. The tensile adhesive strength, thermal shock resistance, porosity, micro-hardness was measured and the results show that:Micro-composite structure of ceramic coating has been achieved with the secondary plating composite powder as raw material via plasma spraying. Fe/Al composite powder can achieve good transition from the metal substrate to the ceramic coating and enhance the performance of ceramic coating. Composite ceramic coating possess higher tensile adhesive strength and better thermal shock resistance. Micro-hardness distribution analysis of the coating is also proved that Fe/Al composite powder can be used as raw material of transitional layer. |
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