Control of helium effects in irradiated materials based on theory and experiment

Mansur, L.K.; Lee, E.H.; Maziasz, P.J.; Rowcliffe, A.F.

doi:10.1016/0022-3115(86)90066-8

Cited by 152 publications

(60 citation statements)

References 46 publications

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“…7,13,79 Direct exchange with a neighboring solute atom provides an alternative mechanism 79 but is highly unlikely to contribute significantly to diffusion due to the large activation energy for the process. For example, our best estimate of the barrier height in Ni is 3.50 eV, which compares well with that found using an embedded atom model (EAM) potential of 3.1 eV by Adams and Wolfer 79 and means that substitutional He is, essentially, immobile.…”

Section: Substitutional He Migrationmentioning

confidence: 99%

“…As such, the diffusion coefficient by this mechanism is inversely proportional to the vacancy concentration. 7,8,79 If thermal vacancies dominate, the activation energy is given by 7,8,13,79 …”

Section: Substitutional He Migrationmentioning

confidence: 99%

“…[5][6][7][8][9][10][11][12] As such, it aids the nucleation, stabilization, and growth of voids (He bubbles), resulting in swelling of the material. 10,[13][14][15][16] The formation of He bubbles has also been implicated in hightemperature embrittlement of materials. 10,17,18 It is therefore of critical importance to gain a deep understanding of the behavior of He in these materials and the part it plays in the underlying mechanisms of microstructural evolution.…”

Section: Introductionmentioning

confidence: 99%

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First-principles study of helium, carbon, and nitrogen in austenite, dilute austenitic iron alloys, and nickel

et al. 2013

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An extensive set of first-principles density functional theory calculations have been performed to study the behavior of He, C, and N solutes in austenite, dilute Fe-Cr-Ni austenitic alloys, and Ni in order to investigate their influence on the microstructural evolution of austenitic steel alloys under irradiation. The results show that austenite behaves much like other face-centered cubic metals and like Ni in particular. Strong similarities were also observed between austenite and ferrite. We find that interstitial He is most stable in the tetrahedral site and migrates with a low barrier energy of between 0.1 and 0.2 eV. It binds strongly into clusters as well as overcoordinated lattice defects and forms highly stable He-vacancy (V m He n ) clusters. Interstitial He clusters of sufficient size were shown to be unstable to self-interstitial emission and VHe n cluster formation. The binding of additional He and V to existing V m He n clusters increases with cluster size, leading to unbounded growth and He bubble formation. Clusters with n/m around 1.3 were found to be most stable with a dissociation energy of 2.8 eV for He and V release. Substitutional He migrates via the dissociative mechanism in a thermal vacancy population but can migrate via the vacancy mechanism in irradiated environments as a stable V 2 He complex. Both C and N are most stable octahedrally and exhibit migration energies in the range from 1.3 to 1.6 eV. Interactions between pairs of these solutes are either repulsive or negligible. A vacancy can stably bind up to two C or N atoms with binding energies per solute atom up to 0.4 eV for C and up to 0.6 eV for N. Calculations in Ni, however, show that this may not result in vacancy trapping as VC and VN complexes can migrate cooperatively with barrier energies comparable to the isolated vacancy. This should also lead to enhanced C and N mobility in irradiated materials and may result in solute segregation to defect sinks. Binding to larger vacancy clusters is most stable near their surface and increases with cluster size. A binding energy of 0.1 eV was observed for both C and N to a [001] self-interstitial dumbbell and is likely to increase with cluster size. On this basis, we would expect that, once mobile, Cottrell atmospheres of C and N will develop around dislocations and grain boundaries in austenitic steel alloys.

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Section: Substitutional He Migrationmentioning

confidence: 99%

Section: Substitutional He Migrationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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First-principles study of helium, carbon, and nitrogen in austenite, dilute austenitic iron alloys, and nickel

et al. 2013

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“…According to the rate theory of swelling due to void growth in irradiated metals [21,22,23]: under steady-state conditions, the radial growth rate of helium-contained cavity is determined by both excess vacancy flux (S) and helium gas pressure (P g ) that in turn is determined by the content of helium atoms (N g ) in each cavity. The increase in both S and N g in the high-energy neutron damage environment of fusion reactors can lead to the decrease in the critical radius of cavity ( ) for rapid void growth and therefore gives rise to accelerated swelling.…”

Section: Bubble Formation In Dual-beam Irradiated K3-ods Steelmentioning

confidence: 99%

HRTEM study of oxide nanoparticles in K3-ODS ferritic steel developed for radiation tolerance

Hsiung

Fluss

Tumey

et al. 2011

Journal of Nuclear Materials

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Crystal and interfacial structures of oxide nanoparticles and radiation damage in 16Cr-4.5Al-0.3Ti-2W-0.37 Y 2 O 3 ODS ferritic steel have been examined using high-resolution transmission electron microscopy (HRTEM) techniques. Oxide nanoparticles with a complex-oxide core and an amorphous shell were frequently observed. The crystal structure of complex-oxide core is identified to be mainly monoclinic Y 4 Al 2 O 9 (YAM) oxide compound. Orientation relationships between the oxide and the matrix are found to be dependent on the particle size. Large particles (> 20 nm) tend to be incoherent and have a spherical shape, whereas small particles (< 10 nm) tend to be coherent or semi-coherent and have a faceted interface. The observations of partially amorphous nanoparticles and multiple crystalline domains formed within a nanoparticle lead us to propose a three-stage mechanism to rationalize the formation of oxide nanoparticles containing core/shell structures in as-fabricated ODS steels. Effects of nanoparticle size and density on cavity formation induced by (Fe 8+ + He + ) dual-beam irradiation are briefly addressed.

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“…The existence of a critical radius and corresponding critical number of gas atoms as a requirement for cavity growth by excess vacancy absorption is now well established [8]. If the cavity contains a number of gas atoms ng that is less than a critical number of gas atoms, ng, then the critical radius for bias driven cavity growth r£ is larger than the minimum critical radius r^.…”

Section: Cascade-induced Cavity Transitionsmentioning

confidence: 99%

Cascade Diffusion Theory of Displacement-Induced Point Defect Concentration and Flux Fluctuations

Mansur

Brailsford

Coghlan

1987

MSF

Self Cite

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A theoretical approach, which has been developed to assess the fluctuations in point defect concentrations and fluxes to sinks that are induced by the production of point defects in spatially and temporally discrete cascades, is summarized. Solutions for cascade dissipation are outlined for the case where cascades occur in a homogeneous lossy medium as well as for the more involved geometries where cascades occur in the presence of a nearby dislocation or cavity. By superposition of solutions representing discrete cascades under conditions of interest, time profiles of point defect concentrations and fluxes are generated. The profiles exhibit extreme fluctuations. Continuum rate theory results arise by applying limits and approximations to cascade diffusion theory. Application of the theory to microstructural processes shows that property changes, especially creep are affected by the fluctuations.

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Control of helium effects in irradiated materials based on theory and experiment

Cited by 152 publications

References 46 publications

First-principles study of helium, carbon, and nitrogen in austenite, dilute austenitic iron alloys, and nickel

First-principles study of helium, carbon, and nitrogen in austenite, dilute austenitic iron alloys, and nickel

HRTEM study of oxide nanoparticles in K3-ODS ferritic steel developed for radiation tolerance

Cascade Diffusion Theory of Displacement-Induced Point Defect Concentration and Flux Fluctuations

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