Enhanced Surface Finishing of Tungsten Carbide By Using Organic Additives

The mechanical machining and finishing of cemented carbides is associated with high abrasive wear of cutting tools. Electrochemical Machining (ECM) is the technical application of high rate metal dissolution and well established for steels and several non –ferrous metals. ECM is a priory free of mechanical tool wear. Recently the authors investigated the high rate dissolution of cemented carbides in ammonia containing alkaline electrolytes [1]. The electrolyte system is suitable for ECM of tungsten carbide as well as cobalt. A homogenous dissolution of the compound material was achieved. In industrial practice, Electrochemical Machining is used to realize high surface quality of work pieces. The existence of anodic films during the machining step is important in controlling the texture of the machined surface obtained [2]. If the dissolution process is controlled by material transport through a film of compact dissolution intermediate, precipitated products [3] or viscous product layer [4] the surface will occurs bright and shiny. The formation of viscous surface layers can be enhanced by surface active organic additives of the electrolyte [5]. In the present work the authors investigated the effect of different solvents on the surface roughness during ECM of tungsten carbide. The electrochemical experiments were carried out in a channel flow cell. Firstly, an aqueous solution containing 2M ammonia and 1.5M sodium nitrate was used as reference electrolyte. In a second step ethanol and glycol, respectively, were added. Both additives change the conductivity as well as the viscosity of the electrolyte. All samples were investigated by SEM after the ECM experiments. A decreasing surface roughness in the order of water, water/ethanol and water/glycol was achieved. A quantitative evaluation will be given by using laser scanning microscopy.

References

[1] N. Schubert, M. Schneider, A. Michaelis, Electrochemical Machining of cemented carbides, Int. J. Refractory Metals and Hard Materials 47 (2014) 54-60

[2]  J. Bannard, Electrochemical Machining, J. Appl. Electrochem. 7 (1977) 1-29.

[3]  T.P. Hoar, T.W. Farthing, Solid Films on Electropolishing Anodes, Nature 169 (1952) 324–325.

[4]  P. A. Jacquet, The Electrolytic Polishing of Metallic Surfaces, Metal Finishing Vol. 47 (1949) 83.

[5]  J. Bannard, The effect of a surface-active additive on the dissolution efficiency and surface finish in ECM, J. Appl. Electrochem. 7 (1977) 189–195.