Stress-enhanced dynamic grain growth during high-pressure spark plasma sintering of alumina

Applying high pressure during the sintering of ceramic materials is a common practice that allows for a reduction of the sintering temperature and the obtaining of fine-grained microstructures. In this work, we show that the final grain size of submicron alumina increased consistently with applied pressure during low temperature (1000–1050 °C), high pressure (500–800 MPa) spark plasma sintering. Grain size trajectories and microstructural observations indicated that stress-enhanced grain growth occurred during the final stage of the sintering process, whereas thermally controlled grain boundary migration was negligible. We suggest that this dynamic, stress-enhanced grain growth is controlled by grain-boundary sliding, grain rotation and coalescence. A strong correlation was found between calculated creep strain rates and grain growth rates, such as during superplastic deformation.