In Situ Observation of the Microstructure-evolution in Silicon Nitride Ceramics Sintering by Synchrotron Radiation X-ray Computed Tomography

Microstructure-evolution of the silicon nitride ceramics sample during sintering process was investigated by a synchrotron radiation X-ray computed tomography (SR-CT) technique. The projection images of the sample were obtained during the sintering process in real-time. 2-D and 3-D reconstructed images were obtained by treating the projection images of different sintering periods with filter back projection arithmetic and digital image processing methods. From the reconstructed images, three sintering stages of the silicon nitride ceramic sample were clearly distinguished and several sintering phenomena during the sintering process such as grain contact, sintering neck growth and pore spheroidization were observed. Densification rate of sintering process was analyzed from the porosity-time logarithm curve, which was obtained from the reconstructed images of silicon nitride ceramic sample at different sintering time. The three sintering stages and linear relationship between porosity and time logarithm in the middle stage of sintering which has already been described in the traditional sintering theories were clearly observed from the porosity-time logarithm curve. The experiment results are in concordance with the sintering theory and provide effective experimental data for further analysis of the sintering process and the mechanical characteristics of ceramics.