Helium release in uranium dioxide in relation to grain boundaries and free surfaces

2010 ◽  
Vol 268 (11-12) ◽  
pp. 2133-2137 ◽  
Author(s):  
G. Martin ◽  
P. Garcia ◽  
C. Sabathier ◽  
G. Carlot ◽  
T. Sauvage ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Uranium Dioxide ◽  
Free Surfaces

The Measurement of Light Element Segregation Using EDS and EELS

1998 ◽  
Vol 4 (S2) ◽  
pp. 772-773
Author(s):  
J.T. Busby ◽  
E.A. Kenik ◽  
G.S. Was
Keyword(s):  
Grain Boundaries ◽  
Nuclear Reactor ◽  
Reactor Core ◽  
Light Element ◽  
Free Surfaces ◽  
Spatial Redistribution ◽  
Core Components ◽  
Radiation Induced ◽  
Potential Interactions ◽  
Impurity Elements

Radiation-induced segregation (RIS) is the spatial redistribution of elements at defect sinks such as grain boundaries and free surfaces during irradiation. This phenomenon has been studied in a wide variety of alloys and has been linked to irradiation-assisted stress corrosion cracking (IASCC) of nuclear reactor core components. However, several recent studies have shown that Cr and Mo can be enriched to significant levels at grain boundaries prior to irradiation as a result of heat treatment. Segregation of this type may delay the onset of radiation-induced Cr depletion at the grain boundary, thus reducing IASCC susceptibility. Unfortunately, existing models of segregation phenomena do not correctly describe the physical processes and therefore are grossly inaccurate in predicting pre-existing segregation and subsequent redistribution during irradiation. Disagreement between existing models and measurement has been linked to potential interactions between the major alloying elements and lighter impurity elements such as S, P, and B.

INTERFACIAL SEGREGATION IN α-IRON

1993 ◽  
Vol 07 (01n03) ◽  
pp. 528-533 ◽  
Author(s):  
PAVEL LEJČEK
Keyword(s):  
Grain Boundaries ◽  
Alloy Composition ◽  
Solute Segregation ◽  
Silicon Nitrides ◽  
Free Surfaces ◽  
Si Model ◽  
Interfacial Segregation

Measurements of solute segregation to free surfaces and grain boundaries in well-defined samples of α-Fe-Si model alloys revealed pronounced differences. Segregation of C and P and depletion of Si are characteristic for grain boundaries. Cosegregation of Si and N resulting in formation of silicon nitrides prevails at the majority of free surfaces in samples containing nitrogen, but S segregation dominates at the surfaces of nitrogen free samples. The results are summarized from the viewpoint of the type of interface, alloy composition and segregation temperature.

The occurrence of dislocation-free zones at grain boundaries and free surfaces during cyclic deformation

1987 ◽  
Vol 89 ◽  
pp. L31-L34 ◽  
Author(s):  
J.I. Dickson ◽  
S. Turenne ◽  
Hong Bande ◽  
G. L'Espérance
Keyword(s):  
Grain Boundaries ◽  
Cyclic Deformation ◽  
Free Surfaces

Helium Migration Mechanisms in Polycrystalline Uranium Dioxide

2006 ◽  
Vol 985 ◽  
Author(s):  
Guillaume Martin ◽  
Pierre Desgardin ◽  
Philippe Garcia ◽  
Thierry Sauvage ◽  
Gaëlle Carlot ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Nuclear Reaction ◽  
Uranium Dioxide ◽  
Nuclear Reaction Analysis ◽  
Annealing Stage ◽  
Depth Profiles ◽  
Release Mechanisms ◽  
Helium Diffusion

AbstractThis study aims at identifying the release mechanisms of helium in uranium dioxide. Two sets of polycrystalline UO2 sintered samples presenting different microstructures were implanted with 3He ions at concentrations in the region of 0.1 at.%. Changes in helium concentrations were monitored using two Nuclear Reaction Analysis (NRA) techniques based on the 3He(d,α)1H reaction. 3He release is measured in-situ during sample annealing at temperatures ranging between 700°C and 1000°C. Accurate helium depth profiles are generated after each annealing stage. Results that provide data for further understanding helium release mechanisms are discussed. It is found that helium diffusion appears to be enhanced above 900°C in the vicinity of grain boundaries possibly as a result of the presence of defects.

Correlation between structure, energy, and ideal cleavage fracture for symmetrical grain boundaries in fcc metals

1990 ◽  
Vol 5 (8) ◽  
pp. 1708-1730 ◽  
Author(s):  
D. Wolf
Keyword(s):  
Phase Space ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Cleavage Fracture ◽  
Good Description ◽  
Random Boundary ◽  
Free Surfaces ◽  
Symmetrical Tilt ◽  
Boundary Model ◽  
Twist Boundaries

The misorientation phase space for symmetrical grain boundaries is explored by means of atomistic computer simulations, and the relationship between the tilt and twist boundaries in this three-parameter phase space is clucidated. The so-called random-boundary model (in which the interactions of atoms across the interface are assumed to be entirely random) is further developed to include relaxation of the interplanar spacings away from the grain boundary. This model is shown to include fully relaxed free surfaces naturally, thus permitting a direct comparison of the physical properties of grain boundaries and free surfaces, and hence the determination of ideal cleavage-fracture energies of grain boundaries. An extensive comparison with computer-simulation results for symmetrical tilt and twist boundaries shows that the random-boundary model also provides a good description of the overall structure-energy correlation for both low- and high-angle tilt and twist boundaries. Finally, the role of the interplanar spacing parallel to the grain boundary in both the grain-boundary and cleavage-fracture energies is elucidated.

The Segregation of Boron and Its Effect on the Fracture of An Ni3Si Based Alloy

1986 ◽  
Vol 81 ◽  
Author(s):  
W. C. Oliver ◽  
C. L. White
Keyword(s):  
Intermetallic Compound ◽  
Low Temperature ◽  
Grain Boundaries ◽  
Cohesive Energy ◽  
Auger Spectroscopy ◽  
Free Surfaces ◽  
Boron Segregation ◽  
Grain Boundary Fracture ◽  
Boundary Fracture ◽  
The Relationship

AbstractIt is now well established that microalloying additions of B to Ni3Al drastically reduce low temperature grain boundary fracture and consequently increase the ductility of this intermetallic compound. One possible explanation for such effects involves the relationship between boron segregation to grain boundaries and free surfaces, and the resulting effect of such segregation on the cohesive energy of the grain boundaries. This study involves the extension of these concepts to an alloy based on Ni3Si. Auger spectroscopy has been carried out on fractured grain boundaries, grain interiors, and free surfaces to determine how B segregates in Ni3(Si,Ti). The consequences of the segregation of B on the cohesive energy of grain boundaries in Ni3Si based alloys are discussed.

Investigation of the effects of boron on Ni3Al grain boundaries by atomistic simulations

1990 ◽  
Vol 5 (5) ◽  
pp. 955-970 ◽  
Author(s):  
S.P. Chen ◽  
A.F. Voter ◽  
R.C. Albers ◽  
A.M. Boring ◽  
P.J. Hay
Keyword(s):  
Grain Boundaries ◽  
Electronic Band Structure ◽  
Cohesive Strength ◽  
Atomistic Simulations ◽  
Electronic Band ◽  
Free Surfaces ◽  
Embedded Atom ◽  
Band Structure Calculations ◽  
Structure Calculations ◽  
Good Agreement

A series of simulations has been performed on grain boundaries in Ni and Ni3Al with and without boron doping using embedded atom-style potentials. A new procedure of obtaining “reference” data for boron related properties from electronic band structure calculations has been employed. Good agreement with existing experimental structural and energetic determinations was obtained. Boron is found to segregate more strongly to grain boundaries than to free surfaces. Adding boron to grain boundaries in Ni and Ni3Al increases their cohesive strength and the work required to pull apart the boundary. This effect is much more dramatic for Ni-rich boundaries than for stoichiometric or Al-rich boundaries. In some Ni-rich cases, adding boron increases the cohesive strength of the boundary to such an extent that the boundaries become stronger than the bulk. Bulk Ni3Al samples that are Ni-rich produce Ni-rich grain boundaries. The best cohesive properties of Ni3Al grain boundaries are obtained when the boundary is Ni saturated and also with boron present. Boron and nickel are found to cosegregate to the grain boundaries.

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