High resolution microanalysis of binder phase in as sintered WC–Co cemented carbides

Abstract

A direct determination is presented of the as sintered composition of the cobalt rich binder phase in a commercial WC–Co cemented carbide grade (80WC–20Co, wt-%) using atom probe time-of-flight spectrometry and analytical electron microscopy. The carbon content of the binder phase was found to be less than 0·1 at.-% throughout the material and it is shown that this result can be generalised to apply to most commercial cemented carbide materials. A tungsten depleted zone, of the order of 50 nm wide, is present in the binder at the phase boundaries. The observed variation of the tungsten content as a function of distance from the phase boundary could be reproduced by numerically solving the diffusion equation. It can be inferred from these calculations that the tungsten concentration retained in the interior of the submicrometre sized binder phase domains has been frozen-in at approximately 1000°C during cooling after sintering.MST/353