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.

The Cold-Brittleness Regularities of Low-Activation Ferritic-Martensitic Steel EK-181

“…Low-activation ferritic-martensitic steels with 9-12% chromium are thought to be the priority structural materials for fast neutron and thermonuclear reactors [1][2][3]. A significant problem with such materials is their cold brittleness (embrittlement and brittle fracture at low temperatures) [3,4].…”

“…Low-activation ferritic-martensitic steels with 9-12% chromium are thought to be the priority structural materials for fast neutron and thermonuclear reactors [1][2][3]. A significant problem with such materials is their cold brittleness (embrittlement and brittle fracture at low temperatures) [3,4]. The tendency to cold embrittlement is a distinctive property of metals and alloys with a body-centered cubic (BCC) lattice (with the exception of Ta) [3][4][5].…”

“…A significant problem with such materials is their cold brittleness (embrittlement and brittle fracture at low temperatures) [3,4]. The tendency to cold embrittlement is a distinctive property of metals and alloys with a body-centered cubic (BCC) lattice (with the exception of Ta) [3][4][5]. It is well known that face-centered cubic (FCC) alloys do not undergo a ductile-brittle transition when the test temperature is reduced.…”

“…It is well known that face-centered cubic (FCC) alloys do not undergo a ductile-brittle transition when the test temperature is reduced. The reasons for this behavior of materials with different types of crystal lattices currently remain a subject of debate [3][4][5][6][7].…”

“…According to [3,15], the mechanisms for the formation of cold brittleness in metals are based on dislocations and determine the cold brittleness as a structural multistage process. The study of internal friction in metals is an effective method for determining the viscous mobility of dislocations and estimating the coefficient of their viscous drag [16,17].…”