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High-Temperature Corrosion of Protective Coatings for Boiler Tubes in Thermal Power Plants

机译:火力发电厂锅炉管保护层的高温腐蚀

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High-temperature corrosion is a serious problem for the water-wall tubes of boilers used in thermal power plants. Oxidation, sulfidation and molten salt corrosion are main corrosion ways.Thereinto, the most severe corrosion occurs in molten salt corrosion environment. Materials rich in oxides formers, such as chromium and aluminum, are needed to resist corrosion in high-temperature and corrosive environment, but processability of such bulk alloys is very limited. High velocity electric arc spraying (HVAS) technology is adopted to produce coatings with high corrosion resistance. By comparison, NiCr (Ni-45Cr-4Ti) is recommended as a promising alloy coating for the water-wall tubes, which can even resist molten salt corrosion attack. In the study of corrosion mechanism, the modern material analysis methods, such as scanning electron microscopy (SEM), X-ray diffractometry (XRD) and energy dispersive spectrometry (EDS), are used. It is found that the corrosion resistances of NiCr and FeCrAI coatings are much better than that of 20g steel, that the NiCr coatings have the best anti-corrosion properties, and that the NiCr coatings have slightly lower pores than FeCrAI coatings.It is testified that corrosion resistance of coatings is mainly determined by chromium content, and the microstructure of a coating is as important as the chemical composition of the material. In addition, the fracture mechanisms of coatings in the cycle of heating and cooling are put forward. The difference of the thermal physical properties between coatings and base metals results in the thermal stress inside the coatings. Consequently, the coatings spall from the base metal.
机译:对于热电厂中使用的锅炉的水冷壁管来说,高温腐蚀是一个严重的问题。氧化,硫化和熔融盐腐蚀是主要的腐蚀方式。其中,最严重的腐蚀发生在熔融盐腐蚀环境中。需要富含氧化物形成物的材料,例如铬和铝,以在高温和腐蚀性环境中抵抗腐蚀,但是这种块状合金的可加工性非常有限。采用高速电弧喷涂(HVAS)技术生产具有高耐腐蚀性的涂层。相比之下,建议将NiCr(Ni-45Cr-4Ti)用作有前途的水冷壁合金涂层,甚至可以抵抗熔融盐腐蚀。在腐蚀机理的研究中,使用了现代材料分析方法,例如扫描电子显微镜(SEM),X射线衍射仪(XRD)和能量分散光谱仪(EDS)。结果发现,NiCr和FeCrAI涂层的耐蚀性比20g钢要好得多,NiCr涂层具有最佳的防腐性能,并且NiCr涂层的孔隙比FeCrAI涂层稍低。涂层的耐腐蚀性主要取决于铬的含量,涂层的微观结构与材料的化学组成同样重要。此外,提出了涂层在加热和冷却循环中的断裂机理。涂层和贱金属之间热物理性能的差异会导致涂层内部的热应力。因此,涂层从贱金属剥落。

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