High temperature embrittlement of metals due to helium: is the lifetime dominated by cavity growth or crack growth?

Trinkaus, H.; Ullmaier, H.

doi:10.1016/0022-3115(94)90076-0

Cited by 60 publications

(37 citation statements)

References 10 publications

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“…As much as 1500 appm He may be implanted at 10 appm/dpa in the plasma facing walls of tokomaks 19 . The subsequent nucleation of He bubbles at GBs promotes void growth and leads to embrittlement 20 . At large He concentrations and elevated temperatures, bubbles can grow into voids and blisters 21 .…”

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The effect of excess atomic volume on He bubble formation at fcc–bcc interfaces

Demkowicz

Bhattacharyya

Usov

et al. 2010

Applied Physics Letters

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Atomistic modeling shows that Cu-Nb and Cu-V interfaces contain high excess atomic volume due to constitutional vacancy concentrations of ~5%at. and ~0.8%at., respectively. This finding is supported by experiments demonstrating that a ~5-fold higher He concentration is required to observe He bubbles via throughfocus transmission electron microscopy at Cu-Nb interfaces than in Cu-V interfaces.Interfaces with structures tailored to minimize precipitation and growth of He bubbles may be used to design damage-resistant composites for fusion reactors.Unlike pure metals 1 , some materials contain constitutional vacancies that are thermodynamically stable at arbitrarily low temperature, for example grain boundaries (GBs) in ceramics 2 and semiconductors 3 , compounds with wide phase fields like NiAl 4 , and certain metal hydrides 5 . We use atomistic modeling to show that Cu-Nb and Cu-V interfaces contain high constitutional vacancy concentrations.Indirect experimental verification of this prediction is obtained by measuring the critical He concentration at which bubbles become detectable at these interfaces in transmission electron microscopy (TEM).

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The effect of excess atomic volume on He bubble formation at fcc–bcc interfaces

Demkowicz

Bhattacharyya

Usov

et al. 2010

Applied Physics Letters

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“…6,7) Because of the accumulation of helium at the grain boundary due to these mechanisms, the reduction of bonding strength of the grain boundary and grain boundary embrittlement (helium embrittlement) would occur. 8) From the viewpoint of material design and lifetime prediction of components, helium embrittlement is a common and important issue for the structural materials of nuclear plants.…”

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High-Temperature Helium Embrittlement of 316FR Steel

Nogami

Hasegawa

Tanno

et al. 2011

Journal of Nuclear Science and Technology

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The helium embrittlement behavior of 316FR austenitic stainless steel was investigated by a tensile test at 750 C using miniature tensile specimens, which were helium-implanted below 100 C up to 5, 30, and 100 appm using a cyclotron accelerator, and were post-implantation-annealed at 750C for 10 and 100 h. The helium-implanted specimens showed a fully intergranular fracture regardless of the helium concentration and annealing time. No microstructural changes in the as-implanted specimen up to 30 appm and formation of a small number of helium bubbles due to the post-implantation annealing were observed. The gradual release of the helium during the tensile test started after the yielding, and a sharp peak of the helium release was detected in the final fracture phase. The total number of helium atoms released was strongly dependent on the implanted helium concentration, rather than on the annealing time.

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“…The coarsening of gaseous cracklike pores (see, for example, [15] and references therein) requires diffusion of the impurities towards the crack, while elastic deformations arise due to the nonvanishing gas volume and pressure. We also mention the transition of a metastable metallic crystal phase into an insulating amorphous state.…”

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Coarsening Kinetics with Elastic Effects

Brener¹,

Марченко²,

Müller‐Krumbhaar³

et al. 2000

Phys. Rev. Lett.

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We discuss the coarsening process of melt inclusions inside a solid phase. Elastic effects lead to an oblate shape of the particles, resulting in a system with strong diffusional and elastic interactions between inclusions. The usual mean-field approximation breaks down and several independent length scales have to be taken into account. In a system of parallel oriented particles we find scaling laws for the coarsening of the different length scales involved. In particular, the lateral size of the particles obeys a nontrivial growth law, R ϳ t 5͞12 .PACS numbers: 81.10. Aj, 62.20.Mk, 81.40.Np The growth of crystals from the melt or from a solution is a typical example of first-order phase transition. Ostwald ripening is the late-stage process by which a new phase coarsens in order to lower the interfacial free energy. During this process the characteristic length scale of the precipitates increases in time, the supersaturation decreases, and the system moves towards phase equilibrium.The classical coarsening theory was given by Lifshitz, Slyozov, and Wagner (LSW) [1] in the framework of a mean-field approach which is valid in the limit of small volume fractions of the new phase. In this approach all precipitated particles are assumed to be spherical and remote from each other. If the diffusional transport of mass or heat is the limiting kinetics of the process, the average size of the particles grows with a power law in time with an exponent of 1͞3. The particle distribution function shows a characteristic scaling behavior.Novel aspects of kinetics of phase transitions appear if the initial metastable phase is a crystal. Generally, it is known that long-range elastic fields, which are inevitable in this situation, destroy the universal features of LSW growth, allowing other kinetics (see, for example, [2] and references therein). An oblate shape of the inclusions is often observed in experiments [3][4][5] and in computer simulations [2,6].Because of a difference in the densities of the two cooperating phases, part of the crystal surrounding a particle of the new phase becomes deformed if the slow diffusion of the point defects is neglected. This modifies the system's behavior in comparison to an unstressed situation. If one assumes incoherence at the interface, as is definitely the case for the melting process or for gas inclusions, the precipitates have an oblate shape which is more favorable compared to a spherical shape because of its lower elastic energy. This effect leads to a substantial modification of the laws of nucleation and growth [7,8].The main purpose of this Letter is to describe the last coarsening stage of this process which should also be very different from the one of classical LSW theory. The system inevitably arrives at a stage where the characteristic size of the particles is comparable to the distance between them. Indeed, if one assumes that these particles are very oblate lentils of radius R, height h ø R, and distance L between them, the volume fraction D 0 ϳ hR 2 ͞L 3 should remain ...

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High temperature embrittlement of metals due to helium: is the lifetime dominated by cavity growth or crack growth?

Cited by 60 publications

References 10 publications

The effect of excess atomic volume on He bubble formation at fcc–bcc interfaces

The effect of excess atomic volume on He bubble formation at fcc–bcc interfaces

High-Temperature Helium Embrittlement of 316FR Steel

Coarsening Kinetics with Elastic Effects

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