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

通过对快中子辐照AlN陶瓷的显微组织研究，发现在低剂量辐照下，AlN中主要出现了Frenkel缺陷等点缺陷，而在高于1 × 10^<24>n/m^2的高剂量辐照下，在500‰左右的辐照温度下，AlN中也形成了位错环。引入点缺陷后，试样的维氏硬度和断裂韧性提高了约30%，随后位错环的形成进一步提高了这些数值。试样的杨氏模量和弯曲强度不受中子辐照的影响。辐照后等时退火至1400℃后，其维氏硬度恢复到与宏观长度平行。结果表明，AlN的硬度主要受试样中点缺陷数量的影响。中子通量的进一步增加导致AlN的抗弯强度下降，这是由于沿晶界形成微裂纹导致的。晶界微裂纹是由位错环优先形成的各向异性晶格扩展引起的。SiC的点缺陷主要是在1 × 10^<26> n/m^2的中子辐照下产生的，并且在500℃左右的辐照温度下也形成了位错环。含点缺陷的试样经辐照退火后主要表现为维氏硬度和宏观长度的平行恢复。点状缺陷的数量是导致碳化硅辐照硬化的主要因素。研究了快中子辐照后非化学计量尖晶石单晶的缺陷类型及其对力学性能的影响。对于以点缺陷为主的试样，其维氏硬度的变化与宏观长度的变化相对应。另一方面，含有低密度位错环的试样的维氏硬度变化不大。尖晶石硬度升高的主要原因是点缺陷。少

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