Grain growth in millimeter wave sintered silicon nitride ceramics

In this paper, to investigate the effect of millimeter wave heating on grain growth behavior in silicon nitride ceramics, specimens doped various rare earth sesquioxides as additives were sintered using a millimeter wave radiation 28 GHz. Comparative studies of densification, phase transformation, grain growth behavior of silicon nitride fabricated by millimeter wave and conventional sintering were carried out. Microstructure of the specimens was analyzed by scanning electron microscopy (SEM) and image analysis. Fully dense millimeter wave sintered silicon nitride presented a bimodal microstructure exhibiting higher values of fracture toughness and fracture strength than materials processed by conventional heating techniques. Results indicate that millimeter wave sintering is more effective in enhancing the grain growth and in producing the bimodal microstructure than conventional heating. It is also confirmed that the localized heating by millimeter wave radiation is taking place within the samples.