Effect of ball-milling on dislocation generation and grain growth behavior in sintered NbC–Co

Abstract

Widely employed in the fabrication of structural ceramics, ball-milling is a process of mixing or pulverizing powders. Despite its popular use, the effects of ball-milling on grain growth behavior are nevertheless still obscure. In this study, we investigated the effects of ball-milling on grain growth behavior in light of the crystal growth theory in a model NbC–Co system with partially faceted grains. Two kinds of 90NbC–10Co (wt %) samples, with and without ball-milling, were prepared. With ball-milling, the density of dislocations increased considerably. In samples without ball-milling, abnormal grain growth (AGG) occurred from the beginning of liquid phase sintering at 1450°C. In contrast, in samples with ball-milling, grain growth behavior was quite normal and large abnormal grains did not appear up to 96 h of sintering. These observations can be explained in terms of the change in the critical driving force for appreciable growth with dislocation density. The present results also demonstrate that proper mechanical treatment (ball-milling) can be useful for suppressing AGG in cemented carbide systems.