Effect of Co Concentration on Hardness of NiCo Coating Layer Synthesized by Electroplating Method

Abstract

Electroplating is one of coatings method to improve the surface properties of metal substrate against corrosion in industrial parts. Electro-deposition of NiCo coating depends strongly on Co content due to increasing hardness properties. Many parameters can be controlled by electroplating method to obtain optimum coating properties. In the present study, synthesize of NiCo coating layer has been successfully done on low carbon steel substrate with variation of 5, 15 and 20 wt% Co concentration and variation of pH 2 and 2.8 using electroplating method. Heat treatment (HT) was carried out at temperature of 800 °C for 5 h using horizontal heated furnace under argon gas inert. Hardness properties were tested by Vickers hardness before and after heat treated samples. Surface and cross-section morphology was characterized by field emission-scanning electron microscopy (FE-SEM), while chemical content was analyzed by energy dispersive spectroscopy (EDS). Crystal phase formed on coated sample was characterized by X-ray diffraction (XRD). The hardness testing result showed the optimum hardness value was obtained for the sample with Co composition of 15 wt% (499.04 HV) without heat treatment and with Co composition of 20 wt% (490.96 HV) for the heat-treated sample. According to FE-SEM results, it was revealed that the small particle size caused high hardness value on both samples, which heat treatment is one of the factors that affected the particle size. Moreover, XRD characterization identified crystal phase of NiCo formed on the coating layer.