Determination of the average WC grain size of cemented carbides for hardness and coercivity

- Several WC-6wt%Co cemented carbides with normal and broad distribution of WC grains were prepared.
- The WC grain sizes were measured by both equivalent circle diameter method and linear intercept method.
- The lack of correlation between arithmetic average grain size and the physical properties were demonstrated.
- Some new methods based on stereology for calculating the average grain size are derived.

Accurate measurements of WC grain size are required to underpin the development of models to predict the mechanical properties of cemented carbides. Some new stereology methods for calculating the average WC grain size are derived based on the observations that the hardness and coercivity were inversely proportional to the content of coarse WC powders. These average WC grain sizes can be calculated by the linear intercepts or equivalent circle diameters determined on polished 2D cross-sections and it is not required to assume intercepts (one-dimension) or equivalent circle diameters (two-dimension) as the three-dimensional grain size. The average linear intercept l[1,0.5] and average cross section diameters d[2,1.5] are proposed to be used as the average graine size associated with hardness. Mathematically, the average l[1,0.5] is the square of ∑p=1tlp/∑p=1tlp12 and the average d[2,1.5] is the square of ∑p=1tdp2/∑p=1tdp32. The average linear intercept l[1, 0] and average cross section diameters d[2, 1] are proposed to be used as the average graine size associated with coercivity. The average linear l[1, 0] is the arithmetic average intercept and the average cross section diameters d[2, 1] is surface/length average equivalent circle diameter. These average WC grain sizes result in a better description of the relation between physical properties and grain size, especially for cemented carbides with broad distribution of WC grains.