Abstract
The interest in hardmetals with fine grain sizes derives from an understanding that hardness generally increases with a decrease in WC grain size. WC powders with very fine sizes are increasingly becoming available. The use of non-standard terms for these materials can be confusing and benefits could accrue from a rationalisation of the terminology for their description. Their use is also putting new demands on the requirements for testing and characterisation of sintered structures. These issues are considered in detail in this paper together with a review of several models for predicting hardness and magnetic properties from grain sizes. For example, the use of the Hall-Petch model for predicting the relation between the grain size and hardness of hardmetals is discussed. The model appears to be satisfactory for the range of materials currently commercially available. However, extrapolation beyond that range will require some care. Coercivity measurements provide an indirect method for estimating grain size. There are a number of empirical equations available in the literature relating coercivity to grain size. These are also critically examined and it is shown that there is a need for standardisation of the grain size measurement method before agreement can be reached on the most appropriate empirical equation.
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