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超音速火焰喷涂Cr3C2-NiCr涂层在3.5%NaCl溶液中的腐蚀性能及机理

Corrosion behavior of HVOF sprayed Cr3C2-NiCr coating in 3.5%NaCl solution

    摘要
  • 摘要: 采用超音速火焰喷涂(high velocity oxy-fuel, HVOF)技术在Q235钢基体上制备了Cr3C2-NiCr涂层,借助X射线衍射(XRD)和扫描电镜(SEM)等方法分析了涂层的相组成和微观组织,研究涂层与镀铬层在质量分数为3.5% NaCl溶液中的腐蚀性能.结果表明,涂层主要由Cr3C2,Cr7C3和NiCr等相组成,涂层的致密度高,层状结构明显,含少量孔隙.阻抗谱曲线表明,Cr3C2-NiCr涂层对基体的保护作用良好,在NaCl溶液中浸泡时间40 d后,极化电阻为2.8 kΩ,而镀铬层失效严重,极化电阻为300Ω.极化曲线表明,Cr3C2-NiCr涂层在浸泡周期内腐蚀电位平稳,腐蚀电流缓慢增加.镀铬层的腐蚀电位下降较快,腐蚀速率成倍增加.孔洞是影响Cr3C2-NiCr涂层耐蚀性的重要原因,影响镀铬层耐蚀性的主要原因是裂纹.

     

    Abstract: FeNiBSi/Cr3C2 composite coating was deposited on 45 steel by high velocity arc spay process. Microstructure of the coating was analyzed by optical microscopy and scanning election microscopy(SEM). Phases were identified by X-ray diffraction(XRD) analysis. Hot corrosion behavior of the coating was tested under a mixed molten salt of Na2SO4+K2SO4(7DK(:DK)3) at 550-750℃ for 100 h. The results showed that the coating has a typical lamellar structure. Corrosion kinetic curves of the coating at different temperatures approximatively follow the parabolic law. It was clear that the hot corrosion resistance of the coating is much more excellent than that of 20G steel. At 550 and 650℃, the high corrosion resistance is mainly due to the formation of a protective oxide layer which is composed of Fe2O3, Cr2O3 and FeCr2O4. The oxide film is imperfect at 750℃ which cannot effectively block the molten salts. So the hot corrosion resistance is poor at 750℃.

     

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