Densification and Grain Growth of Large-Sized Polycrystalline Al2O3 during a Two-Step Pulsed Electric Current Sintering Process

In this study, transparent polycrystalline Al2O3 with a diameter of 30mm was fabricated by two-step pulsed electric current sintering (TS-PECS) at two different heating rates, 100 and 10 degrees C/min. The overall TS-PECS process was divided into parts and was stopped at various positions along the timeline. The relative density and grain size of the Al2O3 samples obtained from each stop were evaluated. In general, the results show that the heating rate changed the densification rate in each sintering stage but did not strongly affect the final density. However, it dramatically influenced the grain growth of Al2O3. With the higher heating rate, the dynamic grain growth was assumed to enhance the grain growth rate because of the high concentration of defects, especially in the last stage of sintering. Especially, a grain size refinement phenomena was observed during the sintering process of polycrystalline Al2O3 for the first time.