Fabriciton of High Strength NiCo Alloy and Rh Coating Using Electroplating Method

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.