FE-EPMA measurements of compositional gradients in cemented tungsten carbides

Previous studies have shown that carbon diffusion can play a key role in the formation of the Co gradient in functionally graded (FG) WC–Co. Analysis of the carbon composition in the Co binder phase of WC–Co alloys is challenging, however, not only due to the small volume of the Co phase in these materials, but also because of the difficulty in characterizing light elements like carbon within matrices of higher atomic weight. In this study, a method via field emission electron probe microanalysis (FE-EPMA) capable of very fine beam size was developed to measure the carbon composition in the Co phase of graded WC–Co materials. A plateau of 0.8 wt.% carbon was measured for approximately 130 μm from the surface into the sample, followed by a steep drop to 0.55 wt.% and a more gradual decline of carbon into the interior that was accompanied by a corresponding increase in the W gradient within Co pockets of the microstructure. These results are discussed in relation to theory and prior simulations.

► A technique was developed using FE-EPMA to measure C composition in the Co binder of WC–Co alloys. ► Optimized operating conditions were established for C analysis. ► Demonstrated that using alloyed standards provided more accurate results than using pure element standards ► Measured C distribution and confirmed the role of C diffusion in forming the Co gradient ► Measured C compositional profile which verified previously published simulation results