Study On High-temperature Corrosion Resistance Coatings Used On Biomass Boiler

The serious high temperature corrosion problem of biomass boiler tubes severely impacts the running of boilers and maybe takes huge economic loss. Using arc spraying to prepare coatings on surface of the boiler tubes is considered as one of the most efficient approaches. So, the research and development of arc spraying materials and coatings which have excellent property of high temperature corrosion resistances has been one most meaningful subject.According to these problems, a new NiCrTi/304 cored wire has been developed. in this article. Supersonic arc spraying techniques was applied to produce four NC coating on 20G. Microstructures and phase structures of four different component coatings have been analyzed by using modern testing techniques,such as,metalloscope,scanning electron microscopy(SEM),energy dispersive spectrometry(EDS), X-ray diffractometry(XRD), et al. The microhardness, bond strength, cohesive force, thermal shock resistance, high-temperature oxidation resistance and high-temperature corrosion resistance have been studied through a series of experiments.The results show that: The structure of the four coatings as NC1, NC2, NC3andNC4 prepared by supersonic arc spraying consists of such as white solid solutions phases(Fe-Ni solid solutions), small amounts of gray oxides phases(Fe-Cr composite oxide,Fe2O3) and black fine holes and so on. The microscopic structure of coatings appears typical layered structure characteristics. Series of NC coatings have high dense, have no significant massive holes and cracks. Series of NC coatings have quite high hardness, bond strength, cohesive force and favorable thermal shock resistance, can reach the application requirement of boiler tubes. The oxidizing dynamics curve at 800℃of coatings had parabolic law, show excellent high-temperature oxidation resistance. After 100 hours test, high-temperature oxidation resistance of coatings are 12 to16 times that of 20G. The corrosion dynamics curve at 800℃of coatings had parabolic law, show excellent high-temperature corrosion resistance. After 90 hours test, high-temperature corrosion resistance of coatings are 4.4 to9.4 times that of 20G.According to the results of tests and analysis on the structure and properties of these four spraying materials and coatings, conclusions show as follow: NC1 coatings have compact and uniform structure, higher microhardness, enough bond strength, cohesive force and favorable thermal shock resistance, best high-temperature oxidation resistance and high temperature corrosion resistance which can be recommended use on the site as anti-corrosion protecting coatings on biomass boiler tubes so as to be greatly popularized after trying on the site.