Swelling and radiation-induced segregation in austentic alloys

Allen, Todd R.; Cole, James I.; Gan, Jian; Was, Gary S.; Dropek, R.; Kenik, E.A.

doi:10.1016/j.jnucmat.2005.02.008

Cited by 52 publications

(24 citation statements)

References 22 publications

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“…The behavior of Ni appears poorly determined because of the uncertainty in the sign of E b (TS,X; ω 1 ), but a positive value, similar to Co, is much more likely. Overall, these observations are consistent with the RIS of Cr away from and Ni towards vacancy sinks in austenitic stainless steels [1][2][3]. Furthermore, they suggest that Co concentrations will be enhanced and Cu depleted from vacancy sinks.…”

Section: Vacancy-mediated Solute Diffusionsupporting

confidence: 84%

“…We have performed additional calculations in bcc fm Fe to provide data for the elements Sc, Zn, Y, Cd, Lu, and Hg not covered in that study. These calculations were performed in a 128 atom supercell with a greater plane wave cutoff energy of 350 eV, a finer 4 3 Monkhorst-Pack k-point grid, and a near-identical lattice parameter to the previous study [21] (see Appendix A). A comparison of results for the elements Ti, Cu, Zr, Ag, Hf, and Au, between our method and Olsson et al [21], showed that formation energies differed by no more than a few hundredths of an eV, which is more than sufficient for our purposes.…”

Section: Computational Detailsmentioning

confidence: 99%

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Transition metal solute interactions with point defects in fcc iron from first principles

2015

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We present a comprehensive set of first-principles electronic structure calculations of the properties of substitutional transition metal solutes and point defects in austenite (face-centered cubic, paramagnetic Fe). Clear trends were observed in these quantities across the transition metal series, with solute-defect interactions strongly related to atomic size, and only weakly related to more subtle details of magnetic or electronic structure. Oversized solutes act as strong traps for both vacancy and self-interstitial defects and as nucleation sites for the development of protovoids and small self-interstitial loops. The consequent reduction in defect mobility and net defect concentrations in the matrix explains the observation of reduced swelling and radiation-induced segregation. Our analysis of vacancy-mediated solute diffusion demonstrates that below about 400 K Ni and Co will be dragged by vacancies and their concentrations should be enhanced at defect sinks. Cr and Cu show opposite behavior and are depleted at defect sinks. The stable configuration of some oversized solutes is neither interstitial nor substitutional; rather they occupy two adjacent lattice sites. The diffusion of these solutes proceeds by a novel mechanism, which has important implications for the nucleation and growth of complex oxide nanoparticles contained in oxide dispersion strengthened steels. Interstitial-mediated solute diffusion is negligible for all except the magnetic solutes (Cr, Mn, Co, and Ni). Our results are consistent across several antiferromagnetic states and surprising qualitative similarities with ferromagnetic (body-centered cubic) Fe were observed; this implies that our conclusions will be valid for paramagnetic iron.

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Section: Vacancy-mediated Solute Diffusionsupporting

confidence: 84%

Section: Computational Detailsmentioning

confidence: 99%

Transition metal solute interactions with point defects in fcc iron from first principles

2015

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“…The authors concluded that the greater effectiveness of Hf was due to its larger size in the matrix relative to Pt. In a similar study using proton irradiations by Allen et al, [9] the authors concluded that there was no observed benefit of Zr on Cr depletion, although there was a reduction in the enrichment of Ni. While seeming to suggest that Zr had no effect, it should be noted that the reference alloy was irradiated to a lower dose, as compared to the +Zr alloys.…”

Section: Introductionmentioning

confidence: 92%

The Mechanism of Zr and Hf in Reducing Radiation-Induced Segregation in 316 Stainless Steel

Hackett

Busby

Was

2007

Metall Mater Trans A

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The addition of oversized solutes has the potential to reduce the effects of radiation-induced segregation (RIS) in austenitic alloys. This RIS has been implicated as one of several factors in enhancing stress corrosion cracking (SCC) under irradiation, so oversized solute additions could promote SCC resistance. Either Zr or Hf was added to 316-type stainless steel, at levels between 0.05 and 0.37 at. pct. Samples were irradiated with 3 MeV protons to 3 dpa at 400°C and analyzed using high-resolution-scanning transmission electron microscopy (HR-STEM) with energy-dispersive X-ray spectroscopy (EDS), to measure the grain-boundary (GB) composition. The Zr additions substantially reduced the amount of RIS, while the Hf was much less effective. Despite similar sizes, first-principles calculations using the Vienna Ab Initio Simulation Package (VASP) demonstrate that solute-vacancy binding for Zr is 1.05 eV vs 0.69 eV for Hf. This difference results in the greater effectiveness of Zr in reducing RIS, as determined by kinetic rate theory calculations, in agreement with experimentally-measured results.

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“…There is, however, strong experimental evidence that increasing Ni content suppresses void formation. 64,65 The inclusion of small quantities (<1 at.%) of oversized solutes, such as Zr and Hf, in austenitic FeCr-Ni alloys was also found to significantly suppress void formation and radiation-induced segregation (RIS) at grain boundaries.…”

Section: A Defect-solute Interactionmentioning

confidence: 99%

Defect and solute properties in dilute Fe-Cr-Ni austenitic alloys from first principles

2012

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We present results of an extensive set of first-principles density functional theory calculations of point defect formation, binding, and clustering energies in austenitic Fe with dilute concentrations of Cr and Ni solutes. A large number of possible collinear magnetic structures were investigated as appropriate reference states for austenite. We found that the antiferromagnetic single-and double-layer structures with tetragonal relaxation of the unit cell were the most suitable reference states and highlighted the inherent instabilities in the ferromagnetic states. Test calculations for the presence and influence of noncollinear magnetism were performed but proved mostly negative. We calculate the vacancy formation energy to be between 1.8 and 1.95 eV. Vacancy cluster binding was initially weak at 0.1 eV for divacancies but rapidly increased with additional vacancies. Clusters of up to six vacancies were studied and a highly stable octahedral cluster and stacking fault tetrahedron were found with total binding energies of 2.5 and 2.3 eV, respectively. The 100 dumbbell was found to be the most stable self-interstitial with a formation energy of between 3.2 and 3.6 eV and was found to form strongly bound clusters, consistent with other fcc metals. Pair interaction models were found to be capable of capturing the trends in the defect cluster binding energy data. Solute-solute interactions were found to be weak in general, with a maximal positive binding of 0.1 eV found for Ni-Ni pairs and maximum repulsion found for Cr-Cr pairs of −0.1 eV. Solute cluster binding was found to be consistent with a pair interaction model, with Ni-rich clusters being the most stable. Solute-defect interactions were consistent with Ni and Cr being modestly oversized and undersized solutes, respectively, which is exactly opposite to the experimentally derived size factors for Ni and Cr solutes in type 316 stainless steel and in the pure materials. Ni was found to bind to the vacancy and to the 100 dumbbell in the tensile site by 0.1 eV and was repelled from mixed and compressive sites. In contrast, Cr showed a preferential binding to interstitials. Calculation of tracer diffusion coefficients found that Ni diffuses significantly more slowly than both Cr and Fe, which is consistent with the standard mechanism used to explain radiation-induced segregation effects in Fe-Cr-Ni austenitic alloys by vacancy-mediated diffusion. Comparison of our results with those for bcc Fe showed strong similarity for pure Fe and no correlation with dilute Ni and Cr.

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Swelling and radiation-induced segregation in austentic alloys

Cited by 52 publications

References 22 publications

Transition metal solute interactions with point defects in fcc iron from first principles

Transition metal solute interactions with point defects in fcc iron from first principles

The Mechanism of Zr and Hf in Reducing Radiation-Induced Segregation in 316 Stainless Steel

Defect and solute properties in dilute Fe-Cr-Ni austenitic alloys from first principles

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