Effects of Point Defects and Dislocations on Mechanical Properties of Neutron-Irradiated Ceramics

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Basing on the microstructural investigation of fast-neutron irradiated AlN ceramic, it was clarified that point defects such as Frenkel defect were mainly introduced in AlN under low dose irradiation, whereas dislocation loops were also formed under higher dose irradiation than 1x10^<24>n/m^2 at about irradiation temperature of 500ﾟC. Vicker's hardness and fracture toughness of specimens increased about 30% by introduction of point defects and those values further increased by succeeding formation of dislocation loops. Young's modulus and bending strength of the specimens were not influenced by the neutron irradiation. After post-irradiation isochronal annealing up to 1400ﾟC, Vicker's hardness was recovered parallel to that of macroscopic length. It was concluded that hardness of AlN was affected mainly by the amount of point defects in the specimens. Further increase in neutron fluence caused degradation of bending strength of AlN due to the microcrack formed along grain boundary of t … More he specimens. The grain boundary microcracks was caused by the anisotropic lattice expansion due to the preferential formation of dislocation loops.In the case of SiC, point defects would be mainly introduced by the neutron irradiation up to 1x10^<26> n/m^2, and over that fluence dislocation loops were also formed at irradiation temperature of about 500ﾟC. The specimens contained point defects mainly showed parallel recovery of Viker's hardness and macroscopic length by post- irradiation annealing. It was also concluded that the main factor of irradiation hardening in SiC was the amount of point defects.Type of defects and those effects on mechanical properties of non-stoichiometric spinel single crystals were investigated after fast-neutron irradiation. For the specimens containing mainly point defects, the change in Vicker's hardness corresponded to the change of macroscopic length. On the other hand, the specimen containing low density dislocation loops showed slight change in Vicker's hardness. It seemed that the main cause in hardness increase in spinel was point defects. Less