The influence of mill type and milling conditions on the homogeneity of ready-to-press powders

In ready-to-press hardmetal powders a homogeneous distribution of cobalt and grain growth inhibitors in the mixture is desired in order to avoid cobalt lakes and to reduce the sintering temperature and grain growth. This is of particular importance when extra-fine or even nanoscaled hardmetals are to be produced. But, in these cases the grain growth inhibitors and the cobalt particles are usually coarser than the tungsten carbide particles. Therefore appropriate milling conditions have to be used. However, there is still a lack of a test for the quality of the mixture, i.e. the homogeneity of the distribution of the constituents. The paper presents a method for controlling the homogeneity of these hardmetal constituents and the effect of the mill type. Differences in the quality of powders milled in an attritor and a ball mill are made visible. The results were obtained using nano-scaled WC powder but are also valid for coarser powders.