NiCrBSi超音速火焰喷涂层的电化学腐蚀机制

采用超音速火焰喷涂方法在普通碳钢表面制备了NicrBsi合金涂层，然后将涂层在利用冰醋酸调整pH值到3的3．5％NaCl(质量分数)溶液中进行全浸泡试验．应用化学成分分析、电子探针分析方法分析了涂层腐蚀后的成分变化和分布，用高频等离子体发射光谱仪分析了腐蚀液中的离子存在情况，用X射线能谱分析了腐蚀产物，用扫描电镜观察了涂层腐蚀后的形貌．结果发现：NiCrBSi合金涂层没有发生成分选择性腐蚀；涂层的腐蚀包括表面宏观均匀腐蚀和腐蚀介质侵入涂层内部引发的腐蚀，后者起关键作用；腐蚀首先在涂层表面存在未熔颗粒及孔隙、夹杂和微裂纹的局部阳极区发生，随后沿孔隙、夹杂、微裂纹、层状组织等形成的阳极通道扩展；涂层的主要失效形式是片状或层状剥离；调整喷涂工艺参数以降低涂层的电化学不均匀性或进行封孔处理有助于提高涂层的耐蚀性能．

Corrosion Mechanism of High Velocity Oxy-Fuel Sprayed NiCrBSi Coatings

The NiCrBSi alloy powder was sprayed to a low carbon steel substrate using high velocity oxy-fuel (HVOF) spraying, and the corrosion tests were carried out by immersing the specimens in the 3.5% NaCl acidified with acetic acid to give a pH of 3. Techniques such as scanning electron microscopy (SEM) observing, high frequency plasma emission spectral analysis, electron probe micro-analysis (EPMA) and X-ray energy-dispersive analysis were employed to study the corrosion mechanism of the coating. It is found that the composition selective corrosion does not occur within the NiCrBSi coating, and the main reason is that electrolyte has penetrated into the inner part of coating. The corrosion first occurs on the surface of the coating around the particles that have not fused during spraying and the defects such as porosities, inclusions and micro cracks, and then develops along the paths formed by porosities, micro cracks, laminar structure, and so on. The main failure mechanism of the coating is exfoliating or laminar shell-off. Adjusting the thermal spraying parameters to reduce the electrochemical unevenness or sealing the porosities could improve the corrosion resistance of the coating.