Amorphous Transformation of Laves Phase in Zircaloy and Austenitic Stainless Steel Upon Neutron Irradiation PDF Download
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Author: LL. Harris
Publisher:
ISBN:
Category : Amorphous transformation
Languages : en
Pages : 15
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Book Description
A variety of forms of irradiation have been observed to induce an amorphous phase: heavy ion, proton, and electron. More recently neutron irradiation has been observed to induce an amorphous transformation in Laves precipitates found in Zircaloy and austenitic steel. Up to this point, only conjectures have been made about the irradiation conditions necessary to achieve the amorphous transformation and about the characteristics of a material susceptible to the amorphous transformation. From these conjectures, a theory to explain the amorphous transformation is developed, and its application illustrated by simulation with a computer model. The amorphous transformation of the Zr(Fe, Cr)2 phase in Zircaloy induced by neutron irradiation is used as the example in the model. The theory proposes that during irradiation the free energy of the crystalline state increases beyond that of the amorphous state, and thus in efforts to minimize the free energy of the system the amorphous transformation occurs. The factors that contribute to this increase in free energy include the defect formation energies and the energies of mixing that arise as the lattice is disordered. The later contribution is found to be significant. It is this factor that makes the amorphous transformation possible at defect concentrations lower than required for transformation when defect generation alone is considered.
Author: LL. Harris
Publisher:
ISBN:
Category : Amorphous transformation
Languages : en
Pages : 15
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Book Description
A variety of forms of irradiation have been observed to induce an amorphous phase: heavy ion, proton, and electron. More recently neutron irradiation has been observed to induce an amorphous transformation in Laves precipitates found in Zircaloy and austenitic steel. Up to this point, only conjectures have been made about the irradiation conditions necessary to achieve the amorphous transformation and about the characteristics of a material susceptible to the amorphous transformation. From these conjectures, a theory to explain the amorphous transformation is developed, and its application illustrated by simulation with a computer model. The amorphous transformation of the Zr(Fe, Cr)2 phase in Zircaloy induced by neutron irradiation is used as the example in the model. The theory proposes that during irradiation the free energy of the crystalline state increases beyond that of the amorphous state, and thus in efforts to minimize the free energy of the system the amorphous transformation occurs. The factors that contribute to this increase in free energy include the defect formation energies and the energies of mixing that arise as the lattice is disordered. The later contribution is found to be significant. It is this factor that makes the amorphous transformation possible at defect concentrations lower than required for transformation when defect generation alone is considered.
Author: F. A. Garner
Publisher: ASTM International
ISBN: 0803109628
Category : Conferences
Languages : en
Pages : 919
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![101 [Hunderteins] Fragen und Antworten über Republik China PDF](https://books.google.com/books/content/images/frontcover/vW--jwEACAAJ?fife=w80-h100)
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Category :
Languages : en
Pages :
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Category : Metallurgy
Languages : en
Pages : 810
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Author: Arthur Moses Thompson Motta
Publisher:
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Category :
Languages : en
Pages : 170
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Author: WJS Yang
Publisher:
ISBN:
Category : Amorphous transformation
Languages : en
Pages : 15
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Book Description
Zircaloy-4, a zirconium base alloy used extensively as cladding and core structural material in water cooled nuclear reactors, was examined by transmission electron microscopy after neutron irradiation and postirradiation annealing. Phase instabilities found during irradiation include the amorphous transformation and the dissolution of intermetallic precipitate Zr(Fe,Cr)2 in the ?-recrystallized matrix and the dissolution of the metastable precipitate Zr4(Fe,Cr) in the ?-quenched matrix. The alloy is driven toward a single phase solid solution during the irradiation. The presence of fast diffusion iron species in the matrix due to the precipitate dissolution may have caused the irradiation growth breakaway phenomenon. The microstructural evolution during irradiation consists of ̄c dislocation development and grain boundary migration. The presence of ̄c dislocations indicates permanent strain in the matrix. The postirradiation annealing at 833 K does not anneal out the ̄c dislocations. The ̄c dislocation is postulated to have developed due to the intergranular constraints under the continuous growth in the breakaway region.
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Category : Aeronautics
Languages : en
Pages : 892
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Category : Alloys
Languages : en
Pages : 1040
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Author: AT. Motta
Publisher:
ISBN:
Category : Charged-particle irradiation
Languages : en
Pages : 22
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Book Description
The crystalline-amorphous transformation of the intermetallic precipitates Zr(Cr,Fe)2 and Zr2(Ni,Fe) in Zircaloy under charged-particle and neutron irradiation is studied.
Author:
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Category :
Languages : en
Pages : 19
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Book Description
At neutron flux levels typical for Zircaloy fuel cladding in commercial power reactors, there is insufficient thermal energy below about 600 K to maintain long-range order in hexagonal close packed (hcp) Zr(Fe, Cr)2 precipitates, and these Laves-phase intermetallics gradually become amorphous. The transformation is homogeneous with no change in composition at low temperatures, but above 500 K an amorphous zone containing only 10 at% Fe grows inward from the periphery as Fe moves outward to the adjacent alloy matrix. The shrinking central cores of Zr(Fe, Cr)2 precipitates in Zircaloy-4 remain crystalline, while in Zircaloy-2 these precipitates quickly undergo partial transformation and the low-Fe amorphous front advances into a random mixture of amorphous and crystalline regions, each with the original composition. Above 600 K, the Zr(Fe, Cr)2 precipitates tend to retain both their hcp structure and original chemical composition. These observations suggest that a dynamic competition between kinetic excitation to an amorphous state and thermal recrystallization makes some fraction of the Fe atoms available for flux-assisted diffusion to the alloy matrix by displacing them from hcp lattice positions into metastable, probably interstitial, sites. With one set of kinetic constants, a simple analytic representation of these processes accurately predicts precipitate amorphization as a function of neutron flux, temperature, and time for either Zircaloy-2 or -4. By implication, over the composition range of interest, hcp Zr(Fe, Cr)2 is most stable thermodynamically with about 33 at% Fe, typical of Zircaloy-2, but amorphous Zr(Fe, Cr)2 has the smallest activation energy for recrystallization with the slightly higher Fe content typical of Zircaloy-4.
