Cold brittleness of metals as a structural multistage dislocation process

Abstract

The cold brittleness of metals under conditions "before --- during --- after" irradiation in nuclear and thermonuclear reactors is considered. The conditions and mechanisms of cold brittleness are determined depending on the type of their crystal lattices, structures, physical and mechanical properties and external influences (temperature, stress, reactor irradiation). The mechanisms of cold brittleness are dislocational and define cold brittleness as a structural multistage process. Stress relaxation at the front of a subcritical crack stops its growth (cold brittleness is not formed). The stacking fault energy of the metal determines the critical level of stress for the beginning of its relaxation by mechanical twinning at the crack front (external stress concentrator). In irradiated metals (cold-brittle "before" irradiation), the temperature range of cold-brittleness expands. "During" irradiation, cold brittleness is not formed. Keywords: alloys, steels, low temperatures, reactor irradiation, crack nucleation, brittle fracture, stages, mechanisms.