镀液pH值对电沉积Ni-W合金镀层结构及其耐蚀性能的影响

Effect of pH Value on Structure and Corrosion Resistance of Electrodeposited Ni-W Alloy Coating

采用直流电沉积的方法在低碳钢表面制备了一层Ni-W合金镀层,研究了pH值对电沉积Ni-W合金镀层结构及其耐蚀性能的影响。结果表明:在硫酸盐-柠檬酸镀液体系中可直接沉积一层均匀致密的Ni-W合金层,pH值小于7的镀液沉积得到纳米晶结构的Ni-W镀层;pH值大于7时,镀层为非晶态结构。Ni-W合金层的硬度主要由镀层中W含量所决定,镀液pH值为5.5时所沉积的Ni-W镀层中W含量最高,镀层的硬度最高(753 HV);在3.5%(质量分数)NaCl溶液中,Ni-W合金层均表现出比低碳钢更低的电化学活性,对基体具有良好的保护作用。在所有的Ni-W合金镀层样品中,非晶态镀层由于表面易发生钝化而具有更加优异的耐蚀性能,其中镀液pH值为7.5时所沉积的镀层具有最优的耐蚀性能。

Ni- W alloy coating was electrodeposited on low- carbon steel from an aqueous citratesulphate,while the effect of pH value on surface state, structure and corrosion resistance of the NiW alloy coatings was investigated. The result shows that： nanocrystalline Ni-W alloy coatings were produced when pH7, while amorphous Ni-W alloy coatings were electrodeposited when pH7.The hardness of Ni-W alloy coatings is correlated with the W content in the alloy coating. In contrast with low-carbon steel, Ni-W alloy coatings show much positive corrosion potential and much lower corrosion current density. Furthermore, the amorphous Ni- W alloy coating electrodeposited by pH=7.5 shows the best corrosion resistance due to the peculiar passivity of the coating in 3.5%（mass fraction） NaCl.