Application of response surface methodology in optimizing electroplating parameters of nickel interlayer on tungsten carbide

Abstract

Tungsten carbide (WC-Co) is categorized as a high wear resistance and fracture toughness material. But, these tool materials are found to wear rapidly when machining some particular workpieces. Various techniques have been proposed to improve the WC-Co performance. One such technique is by diamond coating WCCo. This was done due to its outstanding mechanical properties. Poor adhesion of the coating onto the substrate is the main technical barrier. This is due to the presence of cobalt in the cemented carbide which produces graphite layer. Pre-treatment step is always needed because the nucleation of specific coating is greatly affected by the initial surface conditions of the substrate. In this study, nickel was used as an interlayer and the Watt bath electroplating technique was employed to deposit a thin layer with good adhesion strength. Effect of electroplating parameters such as current density, bath temperature and surface roughness of substrate were studied. Coating thickness, hardness and surface morphology were investigated according to an experimental plan. Subsequently, full factorial experimental design followed by analysis of variance (ANOVA) were applied to analyze the statistical data. Performances of the nickel coating on the WC-Co substrate were analyzed and evaluated using Response Surface Methodology (RSM). The electrodeposition parameters have a great influence on Ni coatings properties. One can observe that lower current density produced more compact morphology and fined grain size. Increase in the thickness of Ni coatings occurred by increasing current density. Comparatively, bath temperature did not have a notable effect on coatings thickness but had great influence on surface morphology and adhesion strength of coatings. Further observation on nickel deposition found that, current density ˜4 to 5 A/dm2, bath temperature =60oC and surface roughness =0.5µm have apparent effects on excellent quality of Ni coatings on tungsten carbide especially in producing a thin layer of coating