Irradiation-Induced Recrystallization of Cellular Dislocation Networks in Uranium-Molybdenum Alloys

2000 ◽  
Vol 650 ◽  
Author(s):  
J. Rest ◽  
G. L. Hofman
Keyword(s):  
Dislocation Structure ◽  
Cell Walls ◽  
Subgrain Boundary ◽  
Lattice Parameter ◽  
Theoretical Description ◽  
Rate Theory ◽  
Dislocation Loops ◽  
Stored Energy ◽  
Molybdenum Alloys ◽  
Structure Calculations

ABSTRACTWe developed a rate-theory-based model to investigate the nucleation and growth of interstitial loops and cavities during low-temperature in-reactor irradiation of uranium-molybdenum alloys. Consolidation of the dislocation structure takes into account the generation of forest dislocations and capture of interstitial dislocation loops. The theoretical description includes stress-induced glide of dislocation loops and accumulation of dislocations on cell walls. The loops accumulate and ultimately evolve into a low-energy cellular dislocation structure. Calculations indicate that nanometer-size bubbles are associated with the walls of the cellular dislocation structure. The accumulation of interstitial loops within the cells and of dislocations on the cell walls leads to increasing values for the rotation (misfit) of the cell wall into a subgrain boundary and a change in the lattice parameter as a function of dose. Subsequently, increasing values for the stored energy in the material are shown to be sufficient for the material to undergo recrystallization. Results of the calculations are compared with SEM photomicrographs of irradiated U- 10Mo, as well as with data from irradiated UO2.

Effect of Formation and Growth of Dislocation Loops and Cavities on Low-Temperature Swelling of Irradiated Uranium-Molybdenum Alloys

1998 ◽  
Vol 540 ◽  
Author(s):  
J. Rest ◽  
G. L. Hofman ◽  
I. I. Konovalov ◽  
A. A. Maslov
Keyword(s):  
Low Temperature ◽  
Rate Theory ◽  
Subgrain Structure ◽  
Dislocation Loops ◽  
Loop Formation ◽  
Molybdenum Alloys ◽  
Fission Gas ◽  
Swelling Mechanism ◽  
Test Reactor ◽  
Low Irradiation

AbstractScanning electron photomicrographs of U–10 wt.% Mo irradiated at low temperature in the Advanced Test Reactor (ATR) to about 40 at.% burnup show the presence of cavities. We have used a rate-theory-based model to investigate the nucleation and growth of cavities during low-temperature irradiation of uranium-molybdenum alloys in the presence of irradiation-induced interstitial-loop formation and growth. Our calculations indicate that the swelling mechanism in the U–10 wt.% Mo alloy at low irradiation temperatures is fission-gas driven. The calculations also indicate that the observed bubbles must be associated with a subgrain structure. Calculated bubble-size-distributions are compared with irradiation data.

On the interpretation of dislocation-loop growth during in-situ high-voltage Electron Microscopy

1990 ◽  
Vol 48 (4) ◽  
pp. 532-533
Author(s):  
E. Holzäpfel ◽  
F. Phillipp ◽  
M. Wilkens
Keyword(s):  
Point Defect ◽  
Rate Equations ◽  
Rate Theory ◽  
Dislocation Loops ◽  
High Voltage Electron Microscopy ◽  
Vacancy Migration ◽  
Voltage Electron ◽  
Reaction Rate Theory ◽  
Defect Reactions

During in-situ radiation damage experiments aiming on the investigation of vacancy-migration properties interstitial-type dislocation loops are used as probes monitoring the development of the point defect concentrations. The temperature dependence of the loop-growth rate v is analyzed in terms of reaction-rate theory yielding information on the vacancy migration enthalpy. The relation between v and the point-defect production rate P provides a critical test of such a treatment since it is sensitive to the defect reactions which are dominant. If mutual recombination of vacancies and interstitials is the dominant reaction, vαP0.5 holds. If, however, annihilation of the defects at unsaturable sinks determines the concentrations, a linear relationship vαP is expected.Detailed studies in pure bcc-metals yielded vαPx with 0.7≾×≾1.0 showing that besides recombination of vacancies and interstitials annihilation at sinks plays an important role in the concentration development which has properly to be incorporated into the rate equations.

Rate Theory for Dislocation Loops Evolution in AL-6XN Austenitic Stainless Steel under Proton Irradiation

2018 ◽  
Vol 913 ◽  
pp. 237-246 ◽  
Author(s):  
Yan Xia Yu ◽  
Li Ping Guo ◽  
Zheng Yu Shen ◽  
Yun Xiang Long ◽  
Zhong Cheng Zheng ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Austenitic Stainless Steel ◽  
Supercritical Water ◽  
Proton Irradiation ◽  
Theory Model ◽  
Average Density ◽  
Rate Theory ◽  
Dislocation Loops ◽  
Average Size ◽  
Supercritical Water Cooled Reactor

The average size and density evolution of dislocation loops in AL-6XN austenitic stainless steel, a candidate fuel cladding material for supercritical water-cooled reactor, under proton irradiation were simulated through a rate theory model. The simulation results exhibit relatively good agreement with the experimental results at 563 K. The size and density of defect clusters are calculated under irradiation temperature between 550 K and 900 K and irradiation doses up to 15 dpa which satisfies the working condition in supercritical water-cooled reactor. The fast nucleation between self-interstitials happens at the initial stage of irradiation. The average size of dislocation loops increases while the average density of these loops reduces with the increasing temperature, and the average density approaches to a constant when irradiated at higher irradiation doses. The mechanism is discussed based on the variation of rate constants of defect reactions and the variation of the diffusion coefficients of interstitials and dislocation loops with dose and temperature.

scholarly journals Electron dynamics in strained graphene

2019 ◽  
Vol 33 (28) ◽  
pp. 1930001 ◽  
Author(s):  
Dawei Zhai ◽  
Nancy Sandler
Keyword(s):  
Theoretical Description ◽  
Charge Accumulation ◽  
Electron Dynamics ◽  
Specific System ◽  
Band Structure Calculations ◽  
Local Charge ◽  
Resonant States ◽  
Out Of Plane ◽  
Structure Calculations ◽  
Dirac Formalism

This paper presents a theoretical description of the effects of strain induced by out-of-plane deformations on charge distributions and transport on graphene. A review of a continuum model for electrons using the Dirac formalism is complemented with elasticity theory to represent strain fields. The resulting model is cast in terms of scalar and pseudo-magnetic fields that control electron dynamics. Two distinct geometries, a bubble and a fold, are chosen to represent the most commonly observed deformations in experimental settings. It is shown that local charge accumulation regions appear in deformed areas, with a peculiar charge distribution that favors occupation of one sublattice only. This unique phenomenon that allows to distinguish each carbon atom in the unit cell, is the manifestation of a sublattice symmetry broken phase. For specific parameters, resonant states appear in localized charged regions, as shown by the emergence of discrete levels in band structure calculations. These findings are presented in terms of intuitive pictures that exploit analogies with confinement produced by square barriers. In addition, electron currents through strained regions are spatially separated into their valley components, making possible the manipulation of electrons with different valley indices. The degree of valley filtering (or polarization) for a specific system can be controlled by properly designing the strained area. The comparison between efficiencies of filters built with this type of geometries identifies extended deformations as better valley filters. A proposal for their experimental implementations as component of devices, and a discussion for potential observation of novel physics in strained structures are presented at the end of the paper.

Lattice Parameter, Volume, and Length Changes in Crystals Containing Dislocation Loops

1970 ◽  
Vol 41 (2) ◽  
pp. 814-815 ◽  
Author(s):  
A. N. Goland ◽  
D. T. Keating
Keyword(s):  
Lattice Parameter ◽  
Dislocation Loops ◽  
Length Changes

Quantification of metallic aluminum profiles in Al+ implanted MgAL2O4 spinel by EELS

1991 ◽  
Vol 49 ◽  
pp. 728-729
Author(s):  
N. D. Evans ◽  
S. J. Zinkle ◽  
J. Bentley ◽  
E. A. Kenik
Keyword(s):  
Lattice Parameter ◽  
Dark Field ◽  
Magnesium Aluminate ◽  
Fusion Reactors ◽  
Phase Identification ◽  
Magnesium Aluminate Spinel ◽  
Metallic Aluminum ◽  
Dislocation Loops ◽  
Aluminum Profiles ◽  
Microstructure Of Material

Magnesium aluminate spinel (MgAl2O4) is being considered as an insulator material within fusion reactors because of its favorable damage characteristics. The microstructure of material implanted at 650°C with 2 MeV Al+ ions is shown in cross-section in Fig. 1. Little damage occurs near the surface, whereas at greater depths (0.5 - 1.0 μm) dislocation loops are formed on {110} and {111} planes. Small features thought to be metallic aluminum colloids were observed in the implanted volume near end-of-range. Phase identification by electron diffraction is complicated because the lattice parameter of spinel (0.8083 nm) is almost exactly twice that of aluminum (0.4049 nm). However, the spinel <222> reflection is weak but the aluminum <111> reflection is intense. In <222>sp<111>Al dark-field images of the implanted volume near end-of-range (Fig. 2) the bright 5-10nm diameter features were presumed to be metallic aluminum colloids.

Defect clusters of molybdenum alloys bombarded by HVEM

1978 ◽  
Vol 36 (1) ◽  
pp. 402-403
Author(s):  
N. Igata ◽  
A. Kohyama ◽  
H. Murakami ◽  
K. Itadani ◽  
H. Tsunakawa
Keyword(s):  
Incident Beam ◽  
In Situ Observation ◽  
Dislocation Loops ◽  
Defect Clusters ◽  
Voltage Electron ◽  
Molybdenum Alloys ◽  
Damage Process ◽  
Hot Rolled

As a simulation study of heavy radiation damage by neutrons, in-situ observation of damage process in molybdenum alloys was performed by a high voltage electron microscope. The objectives of this study are to clarify the processes of defect cluster nucleation and growth, and the role of alloying elements on these in the temperature range from 300K to 1300K.The used molybdenum alloys were Mo-(150-1000)at.ppm.C, Mo-(0.06-0.6)at.%Nb, MO-0.29at.%Hf, MO-(0.026-26)at.%Re and Mo-0.56at.%Ni. The used materials were electron-beam melted and hot rolled at 200-400°C and annealing was performed in the vacuum of l×l0-7torr. at 1800°C for 1.0 hr. The standard irradiation conditions were as follows,Accelerating voltage: 1250KV, Beam intensity: l-6×l019 e/cm2 sec, Incident beam direction: <100>, g-vector: {110},The density of defect clusters was determined by the thickness gradient method.The logarithmic density of interstitial dislocation loops, logNi, increased with the reciprocal irradiation temperature, 1/T. The relation between logNiand 1/T was divided into two Arrhenius type relations above and below 500K.

The structure of rapidly solidified Fe-Ni-Mo-Co-B ribbons

1989 ◽  
Vol 47 ◽  
pp. 290-291
Author(s):  
D. M. Vanderwalker
Keyword(s):  
Electron Microscopy ◽  
Cell Walls ◽  
Lattice Parameter ◽  
Rapid Solidification Processing ◽  
Solidification Processing ◽  
Casting Technique ◽  
Transmission Electron ◽  
Structural Applications ◽  
Melt Spun ◽  
Rapidly Solidified

Fundamental aspects of solidification can be examined by experimentation in rapid solidification processing. The structure produced depends on parameters such as cooling rate, degree of undercooling, heat flow, and growth rate. Rapidly solidified iron base alloys are being developed for structural applications.RSR I Fe-19.7Mo-14.4Ni-7.3Co-1.9Bwt % and RSR II Fe-15.0Ni-11.1Mo-7.4Co-0.84B wt% ribbons were melt spun by a jet casting technique. RSR I ribbons were annealed for one hour at 816°C.Specimens were prepared for transmission electron microscopy by punching 3 mm discs from ribbons and electropolishing in a methanol 5% perchloric acid solution.The TEM was performed on the JEM 200CX electron microscope.As solidified RSR I was found to be canposed of fine (7nm) polycrystalline α-Fe. There is evidence for the presence of Ni Mo and FeB (Fig.1). On annealing, the α-Fe transforms to γ-Fe and FeB2Mo2, with significant grain growth (Fig.2). The as-solidified RSR II contains cellular γ-Fe with fcc-Fe2 3B6 of lattice parameter a=l.067nm at the cell walls (Fig. 3).

EELS of colloids in Mg+ implanted MgAl2O4 spinel

1994 ◽  
Vol 52 ◽  
pp. 980-981
Author(s):  
N. D. Evans ◽  
S. J. Zinkle
Keyword(s):  
Electron Diffraction ◽  
Elevated Temperatures ◽  
Lattice Parameter ◽  
Dark Field ◽  
Phase Identification ◽  
Dislocation Loops ◽  
Void Swelling ◽  
Electron Energy Loss Spectrometry ◽  
Diffraction Patterns ◽  
Electron Energy Loss

Because magnesium aluminate spinel (MgAl2O4) shows a strong resistance to void swelling during neutron irradiation at elevated temperatures, it is a candidate material for specialized applications in proposed fusion reactors. During implantation at 25°C with 2 MeV Mg+ ions to ∼2.8 × 1021 Mg+/m2, dislocation loops are formed at midrange depths (∼0.5 - 1.0 μm) on {110} and {111}. The microstructurc in the implanted ion region (∼1.5 - 2.0 μm) is shown in cross-section in Fig. 1. Within this implanted ion region, small features (4 - 10 nm diam.) were observed in dark field (DF) images using a spinel 222 reflection (Fig. 2). No evidence was found in electron diffraction patterns to suggest these features are (hexagonal) metallic Mg. However, in an earlier study, similar features in Al+ implanted spinel were identified by parallel electron energy loss spectrometry (PEELS) as metallic Al colloids. Phase identification of metallic Al within this spinel by electron diffraction is complicated because the lattice parameter of spinel (0.8083 nm) is almost exactly twice that of aluminum (0.4049 nm) and the phases are oriented cube-on-cube.

Sign in / Sign up

Export Citation Format

Share Document