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 NbCCo system with partially faceted grains. Two kinds of 90NbC10Co (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.

Strategies and practices for suppressing abnormal grain growth during liquid phase sintering

“…This can change the variation of growth rate with driving force from an exponential to a parabolic dependence (Figure ). Yang et al studied the effect of ball milling on grain growth behavior in the NbC‐Co system. Powders of composition 90NbC‐10Co (wt%) were mixed in ethanol for 24 hours with and without WC‐Co balls.…”

“…Samples were prepared from powders mixed (A) without and (B) with WC ‐Co balls. SEM micrographs of (C) sample from powder mixed without WC ‐Co balls sintered at 1450°C for 30 min, and (D) sample from powder milled with WC ‐Co balls sintered at 1450°C for 96 h (reprinted with permission from the Ceramic Society of Japan)…”