Microstructural defects in SiC neutron irradiated at very high temperatures

Microstructures in high purity β-SiC irradiated with fast neutrons (up to ∼9.6 x 1025 n/m2, in HFIR) at very high temperatures (1130, 1300, and 1460 deg. C) were studied by transmission electron microscopy. Cavities and dislocation loops were generally observed in irradiated samples. The cavities were preferentially formed at grown-in stacking faults, and were spherical in shape below 1300 deg. C and mainly faceted with {1 1 1} planes at 1460 deg. C. Estimated volume fractions of observed cavities were much smaller than macroscopic densitometer swelling recently reported, which implies other defects cause the swelling in this temperature regime. Larger Frank loops (>25 nm in radius) formed at 1460 deg. C were identified as interstitial type using the inside/outside method. Unfaulting of the loops was not observed or was very rare. Rapid loop growth and density decrease were observed in the temperature range of 1300-1460 deg. C concurrently with the rapid cavity growth. The limited growth rate of dense loops at lower temperature was discussed in terms of high sink density estimated from a grain-boundary-loop-denuded zone formed at 1130 deg. C