Microstructural Changes in Neutron and Ion Irradiated Silicon Carbide.
ARMY MILITARY PERSONNEL CENTER ALEXANDRIA VA
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Reaction bonded silicon carbide Norton NC 430 was examined with a 100 KV JEOL 100S TEM and a 1200 KV AEI EM7 MK II HVEM for microstructural changes induced by irradiation. Three irradiation modes were used 1 2 x 10 to the 24th power neutronsm square E 1 MeV irradiated at 150 degrees C not annealed. 2 4 x 10 to the 24th power neutronsm square E 1 MeV irradiated at 1100 degrees C. 3 1 and 2 dpa from 4 MeV Ar40 ions at 60 degrees C not annealed. In mode 1, the dislocation density increased by six orders of magnitude to 10 to the 14th powercu m. Dense dislocation tangles were observed adjacent to grain boundaries and voids. No radiation-induce d voids and few black spot defects were observed. In mode 2, the dislocation density was 10 to the 13th power mcu m nut numerous unresolved black spot defects were visible. The individual black spots are Frank dislocation loops with a diameter less than 2 nm. The density of the black spots approach 5 x 10 to the 20th power cm. The argon ion damaged samples showed an unexpected loss of long range order. Neutron damage simulation with heavy ions appears to be rate dependent and may not be suitable for the investigation of ceramic materials. It can be argued that radiation damage in silicon carbide saturates when the vacancy concentration increases sufficiently to allow recombination of interstitials at sites removed from Frank interstitial dislocation tangles. This is evident microstructurally by the high density and small size of the black spots at elevated temperature and fluence. Calculations indicate that neutrons in energy transfers are the driving force in the production of dislocations in the SiC lattice.
- Physical Chemistry