Hardening by point defects in neutron irradiated AIN and SIC

Pressureless-sintered AIN and hot-pressed, pressureless-sintered and reaction-bonded SiC were neutron irradiated at temperatures between 100 and 785°C up to a fluence of 5.2xlO²⁴n/m².The hardness was increased by up to 51% in AIN and 9A% in SiC. The hardness decreased after annealing at temperatures around the irradiation temperature. At the same temperatures, the macroscopic length, which was increased by irradiation, also began to decrease. The hardness and length were almost recovered after 1,200-1,400°C annealing. Thus, hardening in irradiated AIN and SiC is controlled by the number of point defects, or, more precisely, by the strain caused by small point defect clusters which pin down dislocation movement. Dislocation loops were still observed in some samples after 1,400°C annealing while the hardness was almost recovered to that in the unirradiated state. Thus, the existence of dislocation loops is not grounds for hardening in irradiated AIN and SiC.