[en] A new diffusion mechanism describing the changes of the long range order parameter in A15 type compounds after both quenching from high temperatures or low temperature irradiation with high energy particles is presented. It is based on the occupation of nonequilibrium or 'virtual' sites centered halfway between two neighbouring A atoms on 6c sites, arising from the instability of a single 6c vacancy recently found by Welch and coworkers by pair potential calculations. After low temperature irradiation, the occupation of this interstitial site creates the necessary conditions for A <--> B site exchanges over several interatomic distances by focused replacement collision sequences. Due to the occupation of a certain concentration of virtual sites, atomic 'overlapping' is not only possible between A atoms on the chains or between A and B atoms (due to deviations from perfect ordering),but also between B atoms on BBB sequences. The latter are retained after low temperature irradiation only and are responsible for the observed lattice expansion and static displacement. (orig.)

[en] Loss of high temperature ductility due to thermal neutron irradiation was examined by slow strain rate test in vaccum up to 1000⁰C. The results on two heats of Hastelloy alloy X with different boron contents were analysed with respect to the influence of the temperatures of irradiation and tensile tests, neutron fluence and the associated helium production due to nuclear transmutation reaction. The loss of ductility was enhanced by increasing either temperature or neutron fluence. Simple extrapolations yielded the estimated threshold fluence and the end-of-life ductility values at 900 and 1000⁰C in case where the materials were used in near-core regions of VHTR. The observed relationship between Ni content and the ductility loss has suggested a potential utilization of Fe-based alloys for seathing of the neutron absorber materials. Decreasing the impurity boron content is also suggested to be important in increasing the threshold fluence for embrittlement. (author)

[en] The influence of pulsed 4 MeV Ni ion bombardment, with and without simultaneous helium injection, has been explored in a low swelling, Ti-modified austenitic stainless steel. Irradiations were carried out to 70 dpa at 950⁰K; the pulsing frequencies were either 60 s on/off or 1 s on/off. Compared to continuous irradiation, pulsing caused a decrease in the interstitial loop diameter at 1 dpa, although at higher doses the overall dislocation density was not affected. Pulsing and helium both promoted the stability of MC precipitates and retarded the subsequent G phase formation; in some cases G-phase was suppressed and eta phase formed instead. Small bubble-like cavities were observed to grow into large voids after steady dual beam irradiation to 70 dpa. However, this conversion was suppressed by pulse irradiation to 70 dpa and furthermore the sizes of the small cavities were somewhat reduced. The results are explained in terms of current mechanistic understanding of mean point defect kinetics and the evolution of microstructure and microcomposition during irradiation with superimposed annealing periods

[en] Irradiation creep and swelling measurements are reported for Fe-2 1/4Cr-1Mo after irradiation by fast neutrons over the temperature range 370 to 570⁰C. Diameter change measurements on thin walled pressurized tubes in a bainitic condition and density change measurements on rods in a nonstandard condition were made following irradiation in the Experimental Breeder Reactor II. The irradiation creep specimens were irradiated to a fluence of 5.7 x 10²² n/cm² (E > 0.1 MeV) or 30 dpa and the swelling specimens were irradiated to a peak fluence of 2.4 x 10²³ n/cm² or 115 dpa. These results have been used as a basis to establish in-reactor creep and swelling correlations for 2 1/4Cr-1Mo in a bainitic condition. The correlations predict moderate swelling and moderate irradiation enhanced creep at 390⁰C to 480⁰C. The in-reactor creep data at 570⁰C indicates that thermal creep mechanisms become important at this irradiation temperature

[en] In order for radioinduced segregation to occur, certain alloy elements need to be coupled to radioinduced defect fluxes. Some observations of local phase changes in Ni-based alloys during ion bombardment and high-voltage electron-microscopic irradiation are reported in this paper

[en] Nickel, niobium, vanadium, and titanium wire specimens were irradiated with T(d,n) neutrons, Be(d,n) neutrons, or 16-MeV protons to fluence levels ranging from 0.2 to 30 x 10²¹ m^-2. The tensile data indicated that yield strength measurements can provide a reliable method to evaluate the hardening produced by high-energy particle irradiations. The precision of the yield strength data ranged from 0.03 to 0.18 depending on radial flux gradients, material grain size, and wire diameter. Greater variations were observed in the elongation and strain-hardening data; these variations were attributed to the tapered gage sections produced by electropolishing. Tensile elongation and work hardening were also strongly dependent on specimen diameter

[en] In addition to the accumulation of the implanted species, a considerable number of processes can affect the composition of an alloy in the surface region during ion bombardment. Collisions of energetic ions with atoms of the alloy induce local rearrangement of atoms by displacements, replacement sequences and by spontaneous migration and recombination of defects within cascades. Point defects form clusters, voids, dislocation loops and networks. Preferential sputtering of elements changes the composition of the surface. At temperatures sufficient for thermal migration of point defects, radiation-enhanced diffusion promotes alloy component redistribution within and beyond the damage layer. Fluxes of interstitials and vacancies toward the surface and into the interior of the target induce fluxes of alloying elements leading to depth-dependent compositional changes. Moreover, Gibbsian surface segregation may affect the preferential loss of alloy components by sputtering when the kinetics of equilibration of the surface composition becomes competitive with the sputtering rate. Temperature, time, current density and ion energy can be used to influence the individual processes contributing to compositional changes and, thus, produce a rich variety of composition profiles near surfaces. 42 references

[en] Ion beam mixing in Pt-Si bilayered samples was measured during irradiation with projectiles ranging in mass from 4 amu (He) to 131 amu (Xe) at 10⁰K, 300⁰K and 373⁰K. Using deposited damage energy as a basis for comparing the different irradiations, it was found that the heavier ions were more efficient than the lighter ones for inducing mixing. Moreover, it was observed that the mixing was essentially independent of temperature below 373⁰K. These results are interpreted on the basis that the mixing is caused by the stimulated motion of defects during the cooling phase of energetic cascades

[en] The swelling behavior which results from simulated fusion environment irradiation of Fe-10% Cr has been characterized with transmission electron microscopy. Specimens were bombarded at 850 K with: a triple-beam of He⁺, D⁺₂, and 4 MeV Fe⁺⁺ ions to 0.3, 1, 3, 10, 30, and 100 dpa, a dual-beam of He⁺ and 4 MeV Fe⁺⁺ ions to 30 and 100 dpa; and a single-beam of 4 MeV Fe⁺⁺ ions to 30 dpa. The helium and hydrogen injection rates were approx. 10 appm He/dpa and approx. 40 appm D/dpa. Cavities were observed for damage levels of 3 dpa and greater. The swelling was <0.1% for damage levels <30 dpa, but at 100 dpa, there was an increase in the swelling to 2.5% for the triple-beam irradiation and 1.2% for the dual-beam irradiation. The swelling rates between 30 and 100 dpa correlate well with calculated values assuming a steady-state swelling-rate regime has been reached. Calculations show the rapid cavity growth associated with this swelling increase cannot be attributed to equilibrium bubble growth. For all of the bombardments, the cavities with a diameter greater than 10 nm had a truncated octahedral morphology with (111) facets and (100) truncations. Measurements indicate that the surface energy relationship was γ₁₁₁approx. =0.8 γ₁₀₀ for these cavities. At 30 dpa, the cavities in the specimen irradiated with the single-beam technique were larger and had a lower concentration than the specimens irradiated with specimens irradiated with the dual- and triple-ion beams suggests that deuterium has an effect on the damage microstructures in Fe-10% Cr

[en] The propereties of zirconium, zirconium-niobium alloys and beryllium under conditions of logn-term irradiation were investigated. Microstructure, corrosion resistance, radiation growth and swelling of the materials studied were under consideration