化学镀Ni-Co-Cu-P非晶镀层及其耐蚀性能研究

Electroless Deposition and Corrosion Resistance of Ni-Co-Cu-P Amorphous Coatings

摘要:

采用化学镀工艺在45钢表面制备Ni-Co-Cu-P四元合金镀层，通过EDX、XRD、SEM、盐雾试验、Tafel曲线等测试方法研究镀层的成分、晶型结构和耐蚀性能。结果表明：Ni-Co-Cu-P镀层为非晶结构，其中Ni、Co、Cu的含量分别为32.66 wt.%、47.19 wt.%和15.28 wt.%。镀层表面均匀分布着直径约240 ~ 500 nm的球状团簇，一些团簇内部存在纳米级孔隙。镀层经156 h盐雾后出现明显红色锈点，192 h后完全失效。镀层的耐蚀性能明显优于45钢基体和Ni-Co-P镀层。在1.0 wt.% H2SO4溶液中，镀层的自腐蚀电位和腐蚀电流密度分别为-0.26 V和19.17 μA?cm-2，随着电位的升高表面出现大量微裂纹。而在3.5 wt.% NaCl溶液中，镀层表现出活化-钝化-过钝化的腐蚀行为，表面钝化膜逐渐被Clˉ穿透而形成针孔。

Abstract:

Quaternary Ni-Co-Cu-P coatings were synthesized on 45 steel substrates by electroless deposition. The chemical composition, crystal structures and corrosion properties of the coatings were investigated by EDX, XRD, SEM, salt spray tests and Tafel polarization curves. The results indicated that Ni-Co-Cu-P coatings were amorphous with the content of 32.66 wt.% Ni, 47.19 wt.% Co and 15.28 wt.% Cu. Spherical clusters with the diameter of 240 ~ 500 nm were distributed uniformly on the coating surfaces and some clusters contained nano-sized poles. The coatings showed visible red rust points after 156 h and were totally failed after 192 h in neutral salt spray tests. Moreover, corrosion resistance of the coatings was much better than that of the 45 steel substrates and Ni-Co-P coatings. In 1.0 wt.% H2SO4 solution, corrosion potential and corrosion current density of the coatings were -0.26 V and 19.17 μA?cm-2 respectively. By increasing the potential, numerous microcracks emerged on the coating surfaces. In 3.5 wt.% NaCl solution, the coatings exhibited an active-passive-transpassive behavior with passive films penetrated by Clˉ and resulted with pin-holes.