Non-uniform sintering behavior during spark plasma sintering of Y₂O₃

During spark plasma sintering of Y₂O₃ ceramics, the evolution of non-uniform microstructure was observed, depending on the heating rate. At low heating rates, the appearance of the sintered bodies is relatively uniform, and the grain size is slightly larger in the center than in the periphery. At high heating rates, however, the sintered bodies are apparently non-uniform to reveal opaque center and translucent periphery, and a difference in the grain size between the center and the periphery increases remarkably. The porosity and the pore size in the center also increase with holding time. The evolution mechanism of the non-uniform microstructure is explained by using a concept of dynamic grain growth and by assuming defect diffusion from the periphery to the center under complicated electric and magnetic fields during spark plasma sintering.