Research of the effect of large graphite particles on the grain structure of ceramics based on tungsten carbide

Tungsten carbide-based ceramics and hard alloys are widely used as the base for metal-cutting and metalworking tools. The purpose of the work is a metallographic study of the effect of large graphite particles in the initial powder on the grain structure of tungsten carbide-based ceramics produced by spark plasma sintering. Before sintering the ceramic samples, large graphite particles of 50 – 500 μm in size were introduced into the initial powder. Digital image processing and statistical analysis methods were used in the work. It was found that an area of large grains of ~10 μm in size (with a submicron grain size in the material bulk) is formed around the graphite particles identified in metallographic sections of the samples. Similar effect upon contact between the workpiece and the graphite tooling is a consequence of carbon diffusion in tungsten carbide. The area thickness does not depend (within the error limits) on the graphite particle size and is 44 ± 9 μm. It was shown that the size distribution of coarse-grained areas can be approximated by lognormal and exponentially modified Gaussian distributions (the distribution modes are 47 ± 4 and 53 ± 7 μm, respectively). The results obtained and the proposed approach can be used to improve digital image processing techniques for metallographic analysis of the microstructure of materials.

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