V. V. Ovchinnikov

Mössbauer and resistometric study of α(bcc) → γ(fcc) phase transformation induced by ion bombardment and intraphase processes in the Fe + 8.25 at % Mn alloy

The results of the Mössbauer and resistometric studies of the atom redistribution and peculiarities of the α(bcc) → γ(fcc) structure-phase transformation in the Fe + 8.25 at % Mn alloy under irradiation by Ar+ ions (E = 20 keV, j = 50–100 μA/cm2) and heating by a light beam with a comparable power are presented. The Cowley parameter α1 of short-range atomic order, the number and composition of the α and γ phases formed during α → γ transition are calculated. An alternative character of atom redistribution in the quenched alloy caused by irradiation with ions at 250°C (atomic ordering, α1 < 0) and at 420°C (short-range separation, α1 > 0) is established. Exposure to the light beam does not cause a redistribution of atoms at 250°C (α1 = 0). At a temperature of 420°C, exposure to an ion beam repeatedly (1–2 orders of magnitude) accelerates the short-range atomic separation in the alloy and initiates the subsequent transformation of the enriched (up to ~18 at % Mn) zones into the γ phase.

Study of the texture of aluminum alloys after cold rolling, annealing, and irradiation by Ar+ ions

The crystallographic texture of samples (1–3 mm thick) of AMg6, VD1, and 1441 aluminum alloys has been studied after cold rolling, post-rolling annealing, and irradiation by accelerated Ar+ ions (E = 20–40 keV). A feature in common for the {200} and {111} pole figures of samples rolled to a medium degree of reduction (35–72%) is the absence of the pole density at the center of these figures. When the alloys under study undergo post-rolling technological furnace annealing at high temperatures, a texture is formed with a scattered main component of the {001}〈100〉 type, which also occasionally contains orientations from scatter regions of the rolling-texture components. An exposure of the cold-deformed samples to a beam of accelerated Ar+ ions generally leads to analogous textural changes (in the whole volume of the samples irradiated from one side) in a much shorter time and, most frequently, at temperatures 100–200 K lower than in the case of the furnace annealing. In the 1441 alloy, the formation of an unusual two-component cube {001}〈210〉 texture has been noted.

Effect of ion irradiation on the nanocrystallization and magnetic properties of soft magnetic Fe72.5Cu1Nb2Mo1.5Si14B9 alloy

The effect of accelerated Ar+ ions on the crystallization process and magnetic properties of nanocrystalline Fe72.5Cu1Nb2Mo1.5Si14B9 alloy has been studied using X-ray diffraction analysis, transmission electron microscopy, thermomagnetic analysis, and other magnetic methods. Irradiation by Ar+ ions with an energy of 30 keV and a fluence of 3.75 × 1015 cm–2 at short-term heating to a temperature of 620 K (which is 150 K below the thermal threshold of crystallization) leads to the complete crystallization of amorphous alloy, which is accompanied by the precipitation of the α-Fe(Si) solid solution crystals (close in composition to Fe80Si20), Fe3Si stable phase, and metastable hexagonal phases. The crystallization caused by irradiation leads to an increase in the grain size and changes the morphology of grain boundaries and volume fraction of crystalline phases, which is accompanied by changes in the magnetic properties.

Effects of ion irradiation and magnetic field on primary recrystallization of metals

On the example of a cold-rolled (110)[001] single-crystal Fe-3 wt % Si alloy, it has been shown that irradiation by accelerated Ar ions and application of an external magnetic field during annealing exert a substantial influence on the formation of structure and texture upon primary recrystallization.

Radiation Stability of Metal Fe 0.56 Ni 0.44 Nanowires Exposed to Powerful Pulsed Ion Beams

The resistance of Fe0.56Ni0.44 alloy nanowires (fabricated by template synthesis using polymer track membranes) 60 and 100 nm in diameter to radiation with powerful pulsed 85% C+ + 15% H+ ions (E = 20 keV, j = 100 A/cm2, τ = 90 ns) has been investigated. The conclusion that nanosized regions of explosive energy release, so-called thermal spikes, which are thermalized regions of dense cascades of atomic displacements heated to several thousand degrees (in which the thermal pressure can reach several tens of GPa), play an important role in the nanowire structure change is drawn. These are observed as melted nanosized regions on the nanowire surface. Calculations have shown that energy supplied by an ion beam during the action of a single pulse in the used mode (provided that thermal radiation and thermal conductivity serve as energy sinks) can be both sufficient and insufficient to completely melt nanowires depending on their orientation with respect to the ion beam. The bending and failure of nonmelted nanowires is explained by the generation and propagation of post-cascade shock waves.

Effect of powerful pulsed and continuous ion beams on the Al- Cu-Mg alloy structure

The paper considers the results of an electron microscopy study of the VD1 alloy of the Al-Cu-Mg system after cold working and subsequent irradiation with a powerful pulsed ion beam (70% C+ + 30% H+, E = 180 keV) in the pulsed-periodic mode (t = 80 ns, f = 0.1 Hz, j = 200 A/cm2, F = 1-1014 cm-2) and under the conditions of the generation of only one pulse (t = 180 ns, j = 100 A/cm2, F = 2-1015 cm-2). It is established that this irradiation noticeably affects the microstructure of the cold-worked 3 mm thick sheets of VD1 alloy. The initial cellular dislocation structure transforms into a subgrain one. The intensity of structural transformations in the alloy increases with ion current density of a pulse. A similar transformation of a dislocation structure over the entire thickness of the sample is observed under irradiation with continuous Ar+ ion beams (E = 20-40 keV) with not high fluences (1015-1016 cm-2).

Combined ion (Ar+, 20 keV) and light irradiation of the quenched Fe-8.25 at % Mn alloy. Separation between thermal and radiation induced long-range effects

Mossbauer and X-ray diffraction investigations of the radiation-induced α → γ phase transformation and short-range-order formation processes in the quenched Fe-8.25 at % Mn alloy under combined exposure (simultaneous visible light and Ar+ 20-keV ion beam irradiation) are carried out. Combined exposure made it possible to fix the target stationary temperature, and hence, the intensity of thermally-stimulated processes; an energy and ion current density could independently be varied in a wide range. As a result, an important contribution of a non-thermal constituent of ion beam exposure to the structural state of alloy was proved. Only in the presence of ion beam, an α → γ (bcc → fcc) phase transformation and accelerated intraphase processes preparing this transformation are observed in the deep layers of the target (about 103 Rp). With allowance for the relatively low level of thermally and radiation-stimulated processes, radiation-dynamic effects associated with propagation of intense post-cascade solitary waves, which can rearrange metastable matters, are considered as the cause of the observed transformations.