10 research outputs found
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Swelling suppression in phosphorous-modified Fe-Cr-Ni alloys during neutron irradiation
Phosphorous-containing austenitic alloys in the solution annealed condition were irradiated at 745--760/degree/K. The alloys were variations on Fe--13Cr--15Ni--0.05P with respective additions of 0.8 Si, 0.2 Ti, or 0.8 Si /plus/ 0.2 Ti; also included were low (0.01) and zero P compositions (all values in wt. %). The reference ternary and the two phosphorous-only variations contained little precipitation and numerous voids and swelled rapidly, while the three variants containing P with Si and/or Ti showed little or no void formation and profuse phosphide precipitation. Results indicate that phosphorous in solution alone does not have a major influence on void swelling, whereas fine-scale phosphide precipitation is quite effective at eliminating void formation. The principal mechanism restricting swelling is the effect of the dense precipitate microstructure. These precipitates foster profuse cavity nucleation which in turn dilutes the helium atoms (and more time) in order for individual cavities to surpass their critical size and number of gas atoms necessary for subsequent growth as voids. This mechanism for swelling suppression was not found to be particularly sensitive to moderate variations in either the dislocation or cavity densities; the mechanism is strongest at elevated temperature where the critical quantities are large and is less effective at lower temperatures where the critical quantities are small. 19 refs., 10 figs., 3 tabs
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Effects of pulsed dual-ion irradiation on phase transformations and microstructure in Ti-modified austenitic alloy
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 950/sup 0/K; 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
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Fusion-relevant basic radiation effects: theory and experiment
A summary is given of results of the basic radiation effects program at Oak Ridge National Laboratory, which are relevant to fusion reactor materials applications. The basic radiation effects program at ORNL is a large effort with the dual objectives of understanding the atomic and microstructural defect mechanisms underlying radiation effects and of determining principles for the design of radiation resistant materials. A strength of this effort is the parallel and integrated experimental and theoretical approaches in each major research area. The experimental effort is active in electron microscopy, ion irradiations and ion-beam techniques, neutron irradiations, surface analysis and in other areas. The theoretical effort is active in developing the theory of radiation effects for a broad range of phenomena and in applying it to the design and interpretation of experiments and to alloy design