Dependence of the hardness of WC - Co alloys on the character of the distribution of WC grains in size

Abstract

The paper presents the results of studying the dependence of the hardness of WC - Co alloy with a Co content of 10 wt.% on the character of the size distribution of WC grains. An equivalent diameter of the circle with an area matching the cross-section area of the grain was chosen as a grain size of the carbide phase. The WC grain sizes were averaged over their number, area and volume. It is shown that for the alloys with a narrow WC grain size distribution the hardness of the alloys as function of the average grain size follows the Hall - Petch relation. As for a wide distribution, a deviation from this function is observed. It is shown that the use of the area-averaged WC grain size enables description of the hardness as a function of the grain size via a unified Hall - Petch equation, regardless of the nature of the grain size distribution. In this case, the average scatter of hardness values around the trend line does not exceed 12 HV. The use of the volume-averaged grain size in description of the hardness dependence results in practice in a large scatter from the regression line, which is attributed to the error in determination of the content of coarse and very coarse grains, when one needs to measure significantly larger number of grains, as compared to averaging over the area. The results obtained may be used in analysis of single-phase and two-phase materials with grain size distributions with a varying width.