Suppression of Abnormal Grain Growth in WC-Co via Two-Step Liquid Phase Sintering

Microstructure refinement via two-step sintering and its mechanism have been investigated in 92WC-8Co (wt%) alloys. Samples were prepared using conventional and two-step sintering techniques. For conventional sintering, the powder compacts were sintered at 1400 degrees C for various times. For two-step sintering, the powder compacts were heated up to 1500 degrees C, immediately cooled down to 1400 degrees C, and held for various times at 1400 degrees C. In the conventional sintering, > 99% relative density (RD) was obtained after 2 h; however, abnormal grain growth (AGG) occurred. In the two-step sintering, > 99% RD was obtained without AGG for up to 2 h sintering times at 1400 degrees C, showing a uniform microstructure with fine grains of similar to 0.6 mu m in average size. Computer calculation suggested a reduction of the maximum driving force for grain growth right after the first-step sintering at 1500 degrees C. Retardation of AGG in two-step sintering is thus attributed to the change in average grain size and size distribution after the first step of sintering.