PROTON MICROPROBE INVESTIGATION OF THE CAUSES OF PITTING IN CEMENTED TUNGSTEN CARBIDE

The proton microprobe on the EN tandem at the Schonland Centre has bee n applied to determine impurities in cemented tungsten carbide that ha s undergone pitting corrosion. Results of using both a scanning electr on microscope (SEM) and the proton microprobe are presented and compar ed. The results of the proton microprobe investigation identify the im purities as sulphur, iron and molybdenum. The concentrations were too low to be observed in the SEM. On the basis of two-dimensional element al maps obtained with the proton microprobe, quantitative results are presented for the region of interest and a mechanism for the formation of the pits is proposed.