In situ investigation of SiC powder’s microwave sintering by SR-CT technique

Abstract

Microwave sintering is being developed as a novel technique for the preparation of dense structural ceramics, but the mature theory has not been established due to the technical difficulties. The synchrotron radiation X-ray computed tomography (SR-CT) technique was introduced for the first time into the study of microwave sintering to in-situ observe the microstructure evolution of silicon carbide (SiC) material in this paper. By applying the SR-CT technique, the reconstructed 2D and 3D images of the specimen were obtained and the double logarithm curve of mean neck size and time (Ln(x)-Ln(t)) were obtained from these reconstructed images. Various sintering phenomena including sintering neck growth during microwave treatment were observed from the reconstructed images. Furthermore, the differences in microstructure evolution and sintering kinetics between microwave and conventional sintering were analyzed based on the reconstructed images and the Ln(x)-Ln(t) curve. 1) The sharp surface of grains near the contact region distinctly grew blunt and the sintering neck growth between these grains were obviously observed at the early stage. Besides, the larger particles grew faster than smaller ones. The main reason for these phenomena may be the micro-focusing effect of electric fields. 2) During each of the three sintering stages, the sintering kinetics curve of double logarithm relationship between mean neck size and time shows a good linear relationship, but at the middle stage the slope of the curve increases dramatically, which is quite larger than conventional sintering. The preliminary interpretation for these extraordinary phenomena has been discussed in details.