Fabriciton of NiCo Alloy and Rh Coating Using Electroplating Method
The properties of NiCo deposits were analyzed using field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD).
Analysis Lab
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Authored By:
Yong-Soo Lee, Seo-Hyang Lee and Jae-Ho Lee1
Dept. of Materials Science and Engineering, Hongik University
Seoul, Korea
Summary
NiCo alloys are electroplated in sulfate bath. The concentration of cobalt sulfate and current density were varied to optimize the surface hardness. The properties of NiCo deposits were analyzed using field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The surface hardness of the NiCo alloy was increased up to 500Hv at 24 w% Co in the deposits due to the grain refinement. The size of grain was reduced to 12 nm. The residual stress of the deposits was varied from tensile to compressive as the saccharine concentration increased. The zero residual stress was achieved at 0.05 g/L saccharine addition.
The electrodeposition of rhodium (Rh) on silicon substrate at different current conditions were investigated. The cracks were found at high current density during the direct current (DC) plating. The pulse current (PC) plating were applied to avoid the formation of cracks on the deposits. Off time in the pulse plating relieved the residual stress of the Rh deposits and consequently the current conditions for the crack-free Rh deposits were obtained. Optimum pulse current (PC) condition is 5:5 (on:off) for the crack-free Rh electroplating.
Conclusions
The Co contents in alloy was increased linearly with Co2+ ion proportion in the bath. Surface hardness of NiCo alloy reached to maximum 500 Hv at 24 wt% Co contents in the alloy. The size of grain was decreased as Co contents in alloy increased, howevr it reached to 12 nm, even though Co contents in the alloy was increased. The residual stress of the NiCo alloy was lowered by addition of sacchain. It was changed from tensile to compressive and zero residual stresss was achieved at 0.05 g/l of saccharin. Zero residual stressed NiCo alloy was electroplated from 0.2M cobalt sulfate bath with addition of 0.05 g/l saccharin at 40 mA/cm2.
Pulse current plating of Pd can give the high surface hardness up to 800 Hv without heat treatment. The longer off time relieved the internal stress of the coating. And consequently, the residual stress of the Pd coating was reduced after applying pulse current electroplating method.
Initially Published in the SMTA Proceedings
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