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

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 ∼ (10 4 - k×10 5 ) 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 (10 4 - k×10 5 ) 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. © Published under licence by IOP Publishing Ltd

Temperature decrease and multiple acceleration of structural and phase transformations in metastable metals and alloys under cascade-forming irradiation. Part 2 - Experimental Results and Discussion

Part 2 is a continuation of Part 1 of the Review and presenting examples of recent research by the author and his colleagues which confirm the main features of low-dose processes caused by nanoscale dynamic effects under cascade-forming irradiation, namely:(1) a decrease in the temperature of structural and phase transformations by 100-300 K in pure metals and alloys which were initially in nonequilibrium (amorphous, strongly deformed, quenched) states; (2) repeatedly (by 2-3 or more orders of magnitude) increase in the flow rate as compared with thermoactivated processes; (3) propagation of transformations over distances many times exceeding the projected ranges (R p ) of ions (or the ranges of primary recoil atoms under neutron irradiation); theoretically, these distances are unlimited, in practice they reach (10 3 -10 5 )⋅R p and more (up to several mm in aluminum alloys). In the near future, the observed effects may provide a breakthrough in fundamental studies of low-temperature processes in metastable media as well as in processing and design of new functional materials. © Published under licence by IOP Publishing Ltd.The work was fulfilled in the frame of state task project № 0389-2015-0025, supported by the Act 211 of the Government of the Russian Federation (Agreement No. 02.A03.21.0006) and it was supported by the Russian Scientific Foundation, project no. 15-19-10054 (sections 3.1 and 3.4