engleski

Surface properties of the system: Hard metal/Co coating/electrolyte

The surface properties of hard metal were studied usingin situ electrochemical methods (cyclic voltammetry, potentiostatic and galvanostatic methods) in conjunction withex situ techniques (SEM and X-ray diffraction). The samples were prepared by sintering 91% WC and 9% Co binder in vacuum. The present work was inspired by the possibility of eliminating the low wettability of tungsten carbide by means of electrochemical modification of the surface. The hard metal surface was electrocoated with cobalt. In order to improve adhesion of the Co layer an electrolytic method was developed by which the carbide phase was dissolved anodically at 0.2 V with respect to SCE in 4m NaOH solution. Surface investigations by SEM and X-ray diffraction revealed that electrolytic dissolution of the tungsten carbide leaves the cobalt network (the spongy cobalt layer) with a face-centered cubic lattice (-cobalt). Considering the substrate's influence on adhesion and the coating quality, particular attention was given to the conditions of electrodeposition of -cobalt. Low pH values, low temperature, higher current densities strongly promote the deposition of the -modification of cobalt.

91% WC and 9% Co; cobalt; electrodeposition; SEM; X-ray diffraction; electrochemical methods

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