1989 Volume 97 Issue 1132 Pages 1511-1516
In order to clarify how the fracture strength depends on the grain boundary structure in covalent-bonded SiC, 6H-type α-SiC Bicrystals with twist misorientations around ‹0001› axis were prepared by a hot press technique at 2270K under 40MPa in a vacuum of 2.7MPa. The grain boundary structure was observed by high resolution electron microscopy and the fracture strength was measured by the three-point bending test. The results obtained are summarized as follows.
(1) An amorphous-like layer was observed along the boundaries prepared. The structure was like the extended grain boundary reported for sintered SiC. The thickness of the boundary was about 1nm irrespective of the twist misorientation. The thickness is thinner than those observed in sintered SiC probably because of the low index boundary plane.
(2) Twist misorientation dependence of grain boundary strength was weak, which is presumably caused by the isotropic nature of the extended grain boundary.
(3) The extention of the boundary is considered to come of the polarity in SiC because the boundary with a misorientation of 0°±2° extended also.
(4) The boundary structure is thought to depend on the preparing process. Coincidence site lattice boundaries are likely to be formed by sublimation-recrystallization or chemical vapor deposition, while extended grain boundaries are formed by sintering because each grain is constrained by surrounding grains during sintering.