Fracturing of borides under neutron irradiation

The neutron irradiation of high-temperature borides results in high internal stresses. This leads to considerable swelling and micro- and macrofracturing. The results of direct investigations of the boride degradation process under neutron irradiation over a wide range of temperatures and fluences have been summarized. A change in the mechanism of radiation damage of borides within the temperature interval of 400 to 530 C is discussed. The macrocracking with formation of annular and radial cracks is observed below this temperature range. The accumulation of microfractures and the process of gas-induced swelling take place at irradiation temperatures above 530 C. The results obtained were conformed by resistance measurement data. The effect of high internal stresses is compared with that of external pressure. (orig.)