钴含量对电沉积镍-钴合金电沉积机理和力学性能的影响

摘要

在改进的Watts槽中电沉积不同钴含量镍−钴合金涂层，采用电化学阻抗谱方法研究钴含量对涂层电沉积机理的影响。采用SEM和XRD表征涂层的表面形貌和晶体结构。采用维氏显微硬度和拉伸试验确定涂层的力学性能。结果表明，随着电解槽中Co2+离子的增加，镍−钴涂层电荷转移电阻增加，相反Warburg阻抗降低。这可能是因为Co(OH)2阴极表面覆盖范围增大和金属离子向阳极表明扩散速率较高。而且，随着槽中钴含量的增加，合金涂层中的钴含量异常增加，(111)织构逐渐加强。当合金涂层的钴含量增加到45%时，晶粒尺寸减小，随之合金的硬度和强度增大。进一步增加钴含量达55%，合金的硬度和强度稍微降低。在Ni−25%Co涂层中能观察到最大的延展性，这是因为合金具有小晶粒尺寸和致密结构。%Ni–Co coatings with various cobalt contents were electrodeposited from modified Watts bath. The effect of cobalt content on electrodeposition mechanism of the coatings was studied by electro-chemical impedance spectroscopy method (EIS). Surface morphology and crystallographic structure of the coatings were investigated by means of SEM and XRD. Mechanical properties of the coatings were determined using Vickers microhardness and tensile tests. It was found that with increasing the Co2+ions in electroplating bath, the charge transfer resistance (Rct)of Ni−Co film increased whereas the Warburg impedence decreased. This may be due to enhancement in coverage of cathode surface by Co(OH)2 and higher diffusion rate of metal ions towards cathode surface, respectively. Also, with increasing the cobalt content in the bath, cobalt content in the alloy coating increased anomalously and (111) texture consolidated gradually. With increasing the cobalt content up to 45% in alloy coating, the grain size decreased and consequently, hardness and strength of the alloy increased. Further enhancement of cobalt content up to 55% led to a little decrease in hardness and strength. The maximum ductility was observed for Ni−25%Co coating due to relatively small grain size and compact structure.