1979 Volume 87 Issue 1006 Pages 317-321
Compacts of highly pure β-SiC powder with an average size of about 0.1μm were heated up to 2100°C at a heating rate of 5.5°C/min in helium (O2<1ppm and dew point -74°C). Although no apparent shrinkage was observed on the compacts, scanning and transmission electron microscopic observation revealed remarkable microstructural changes during the heating.
The results obtained were as follows:
(1) After heating up to 1630°C, joining and coalescence among particles were observed in the compact. It was found that the coalesced grain was polycrystalline and consisted of many differently oriented grains, of which size was in the range of 0.1 to 0.3μm.
(2) In the compact heated up to 1900°C, the grain growth by about ten times in size was observed, although extensive morphological change among particles occurred without appreciable grain-boundary migration.
(3) During heating up to 2100°C, some parts of the compact was densified almost to its theoretical density, and development of pores took place in other parts. Thus no densification occurred as a whole.
(4) A distribution of dihedral angles was measured from the transmission electron micrographs, and the most frequently observed angle was 92°, which gave a value of 1.39 as the ratio of grain-boundary energy to surface energy. This suggests that virtually no thermodynamic limitation would exist for densification of SiC.
