Temperature decrease and multiple acceleration of structural and phase transformations in metastable metals and alloys under cascade-forming irradiation. Part 1 – General questions and theory

Abstract

Classical radiation physics describes well a number of known phenomena observed under irradiation of metals and alloys (radiation embrittlement, swelling, radiation creep), based on relatively slow processes of thermo- and radiation-enhanced diffusion. Mechanisms based on the description of the defect migration processes can not, however, explain the “low- dose effect” under neutron irradiation and the low-dose “long-range effect” under irradiation with accelerated ions E ∼ (104 – k×105) eV (1<k≲3). The paper is devoted to a brief review of the model that takes into account the nanoscale dynamic effects during cascade-forming irradiation. We are talking about explosive energy release in the regions of dense cascades of atomic displacements (thermal spikes) emitting powerful post-cascaded solitary waves, which can initiate structural-and-phase transformations in metastable media, theoretically, at unlimited distances. The distances at which the effect of accelerated (104 – k×105) eV ion beams is observed (in the continuous irradiation mode) are sometimes more than a few tens/hundreds of micrometers (at projected ion ranges of less than 1 μm) and, as recent studies have shown, can reach 1-10 millimeters. These effects are considered on the basis of experimental research data of more than ten different systems. The foundations of the theory of undamped propagation of plane and spherical waves in metastable media are presented. It is noted that the most probable energy of recoil atoms generated by reactor neutrons and fission fragments also belong to the above energy range, which indicates the need to take into account the nanoscale dynamic effects, regardless of the type of the cascade-forming irradiation.