Study on the Change of Grain Size of WC Powder during Ball Milling of Cemented Carbide

Abstract

The mixing phenomena of WC and Co powders have not yet been made clear enough in spite of their importance in the Cemented Carbide industry. Therefore, in this paper the crushing of WC powders and the behaviour of their grain growth during sintering were examined using variousWC powders, i.e., coarse single crystal, coarse polycrystalline and medium single crystalline WC powders.The obtained results were as follows;(1) Coarse single crystal WC powders were crushed markedly by chipping in the early ball milling stage. There-after, average grain size of WC continued to decrease with the appearance of fine chipping powders. Therefore, the grain size distribution of the coarse single crystal WC powder grew wider with the increase of ball milling time.(2) Polycrystalline WC powders were crushed in the same way as the above mentioned (single crystal) in the early ball milling stage. However, the grain boundary destruction seemed to be caused after having been WC crushed into the definite size.(3) Single crystal WC powder of medium size were more difficult to be crushed with chipping than the coarse one.(4) The grain growth of coarse single crystal WC during sintering is more rapid than polycrystalline one because the size distribution of the former was wider than that of the latter. Moreover the average grain size of WC in alloys formed medium single crystal WC powders in coarser than that from coarse one, because the former was less crushed than the latter.(5) In sum, the crushbility of WC in ball milling and its grain growth in sintering did not only depend upon WC grain size, but also the manufacturing process.