- Rate Theory of Defects Induced by Neutron and Ion Irradiation of Concentrated Fe–Cr Alloys

2016 ◽  
pp. 48-61
Keyword(s):  
Ion Irradiation ◽  
Rate Theory

Radiation-Induced Minor Element Segregation at Austenitic Stainless Steel Grain Boundaries

1996 ◽  
Vol 439 ◽  
Author(s):  
E. P. Simonen ◽  
S. M. Bruemmer
Keyword(s):  
Grain Boundaries ◽  
Neutron Irradiation ◽  
Ion Irradiation ◽  
Austenitic Stainless Steels ◽  
Minor Element ◽  
High Rate ◽  
Rate Theory ◽  
Minor Elements ◽  
Radiation Induced ◽  
Irradiation Behavior

AbstractMeasurement of minor element compositions at irradiated grain boundaries in austenitic stainless steels indicates that Si is the only element that significantly responds to radiation-induced segregation. Other minor elements, such as P or S, do not exhibit elevated grain boundary concentrations after irradiation. A rate theory evaluation of segregation is in accord with ioninduced Si enrichment, but reveals complexities in the interpretation of extrapolating behavior from ion-irradiation to neutron-irradiation behavior. The model calibrated to measured high-rate, ioninduced segregation greatly overestimates measured low-rate, neutron-irradiation segregation of Si.

A Phenomenological Model for the Effect of Nanocrystalline Microstructure on Irradiation-Induced Amorphization In U3Si

1994 ◽  
Vol 373 ◽  
Author(s):  
J. Rest
Keyword(s):  
Critical Temperature ◽  
Grain Boundaries ◽  
Ion Irradiation ◽  
Theory Model ◽  
Rate Theory ◽  
Two Phase ◽  
Thermal Crystallization ◽  
Acoustic Shock Wave ◽  
Radiation Induced ◽  
Nanocrystalline Microstructure

AbstractA rate theory model is formulated wherein amorphous clusters are formed by a damage event. These clusters are considered centers of expansion (CEs), or excess-free-volume zones. Simultaneously, centers of compression (CCs) are created in the material. The CCs are local regions of increased density that travel through the material as an elastic (e.g., acoustic) shock wave. The CEs can be annihilated upon contact with a sufficient number of CCs, to form either a crystallized region indistinguishable from the host material, or a region with a slight disorientation (recrystallized grain). Recrystallized grains grow by the accumulation of additional CCs.Preirradiation of U3Si above the critical temperature for amorphization results in the formation of nanometer-size grains. In addition, subsequent reirradiation of these samples in the same ion flux at temperatures below the critical temperature shows that the material has developed a resistance to radiation-induced amorphization (i.e., a higher dose is needed to amorphize preirradiated samples than those that have not been preirradiated). In the model, it is assumed that grain boundaries act as effective sinks for defects, and that enhanced defect annihilation is responsible for retarding amorphization below the critical temperature by, for example, preventing a buildup of vacancies adjacent to the grain boundaries. The calculations have been validated against data from ion-irradiation experiments with U3Si. For appropriate values of the activation energy of thermal crystallization, the model predicts the evolution of a two phase microstructure consisting of nanocrystalline grains and amorphous clusters.

Effets of surfaces on precipitate morphology in irradiated thin foils

1978 ◽  
Vol 36 (1) ◽  
pp. 654-655
Author(s):  
D.I. Potter ◽  
A. Taylor
Keyword(s):  
Ion Irradiation ◽  
Dark Field Image ◽  
Thin Foil ◽  
Dark Field ◽  
Al Alloy ◽  
Bright Field Image ◽  
Dislocation Loops ◽  
Precipitate Morphology ◽  
Thin Foils

Thermal aging of Ni-12.8 at. % A1 and Ni-12.7 at. % Si produces spatially homogeneous dispersions of cuboidal γ'-Ni3Al or Ni3Si precipitate particles arrayed in the Ni solid solution. We have used 3.5-MeV 58Ni+ ion irradiation to examine the effect of irradiation during precipitation on precipitate morphology and distribution. The nearness of free surfaces produced unusual morphologies in foils thinned prior to irradiation. These thin-foil effects will be important during in-situ investigations of precipitation in the HVEM. The thin foil results can be interpreted in terms of observations from bulk irradiations which are described first.Figure 1a is a dark field image of the γ' precipitate 5000 Å beneath the surface(∿1200 Å short of peak damage) of the Ni-Al alloy irradiated in bulk form. The inhomogeneous spatial distribution of γ' results from the presence of voids and dislocation loops which can be seen in the bright field image of the same area, Fig. 1b.

Xenon ion irradiation of superconducting YBa2Cu3O7 thin films

1990 ◽  
Vol 48 (4) ◽  
pp. 92-93
Author(s):  
H. Watanabe ◽  
B. Kabius ◽  
B. Roas ◽  
K. Urban
Keyword(s):  
Defect Formation ◽  
Ion Irradiation ◽  
High Resolution Electron Microscopy ◽  
Structural Disorder ◽  
Flux Lines ◽  
Pinning Effect ◽  
Magnetic Flux Lines ◽  
Resolution Electron ◽  
Radiation Induced ◽  
Induced Defects

Recently it was reported that the critical current density(Jc) of YBa2Cu2O7, in the presence of magnetic field, is enhanced by ion irradiation. The enhancement is thought to be due to the pinning of the magnetic flux lines by radiation-induced defects or by structural disorder. The aim of the present study was to understand the fundamental mechanisms of the defect formation in association with the pinning effect in YBa2Cu3O7 by means of high-resolution electron microscopy(HRTEM).The YBa2Cu3O7 specimens were prepared by laser ablation in an insitu process. During deposition, a substrate temperature and oxygen atmosphere were kept at about 1073 K and 0.4 mbar, respectively. In this way high quality epitaxially films can be obtained with the caxis parallel to the <100 > SrTiO3 substrate normal. The specimens were irradiated at a temperature of 77 K with 173 MeV Xe ions up to a dose of 3.0 × 1016 m−2.

Structural relationships in the synthesis of cubic boron nitride thin films by ion-assisted deposition

1994 ◽  
Vol 52 ◽  
pp. 638-639
Author(s):  
D. L. Medlin ◽  
T. A. Friedmann ◽  
P. B. Mirkarimi ◽  
M. J. Mills ◽  
K. F. McCarty
Keyword(s):  
Boron Nitride ◽  
Ion Irradiation ◽  
Cubic Boron Nitride ◽  
Film Stress ◽  
Bonded Phases ◽  
Structural Relationships ◽  
Precursor Material ◽  
Pressure Synthesis ◽  
Microstructure Of The Material

The allotropes of boron nitride include two sp2-bonded phases with hexagonal and rhombohedral structures (hBN and rBN) and two sp3-bonded phases with cubic (zincblende) and hexagonal (wurtzitic) structures (cBN and wBN) (Fig. 1). Although cBN is synthesized in bulk form by conversion of hBN at high temperatures and pressures, low-pressure synthesis of cBN as a thin film is more difficult and succeeds only when the growing film is simultaneously irradiated with a high flux of ions. Only sp2-bonded material, which generally has a disordered, turbostratic microstructure (tBN), will form in the absence of ion-irradiation. The mechanistic role of the irradiation is not well understood, but recent work suggests that ion-induced compressive film stress may induce the transformation to cBN.Typically, BN films are deposited at temperatures less than 1000°C, a regime for which the structure of the sp2-bonded precursor material dictates the phase and microstructure of the material that forms from conventional (bulk) high pressure treatment.

Electron and ion irradiation-induced dissolution of mechanical twins in the intermetalic U3Si: An in situ HVEM study

1989 ◽  
Vol 47 ◽  
pp. 652-653
Author(s):  
Charles W. Allen ◽  
Robert C. Birtcher
Keyword(s):  
Elevated Temperatures ◽  
Ion Irradiation ◽  
Ion Beam ◽  
National Laboratory ◽  
Argonne National Laboratory ◽  
Heavy Ion ◽  
High Energy ◽  
Mechanical Twinning ◽  
In Situ Experiments

The uranium silicides, including U3Si, are under study as candidate low enrichment nuclear fuels. Ion beam simulations of the in-reactor behavior of such materials are performed because a similar damage structure can be produced in hours by energetic heavy ions which requires years in actual reactor tests. This contribution treats one aspect of the microstructural behavior of U3Si under high energy electron irradiation and low dose energetic heavy ion irradiation and is based on in situ experiments, performed at the HVEM-Tandem User Facility at Argonne National Laboratory. This Facility interfaces a 2 MV Tandem ion accelerator and a 0.6 MV ion implanter to a 1.2 MeV AEI high voltage electron microscope, which allows a wide variety of in situ ion beam experiments to be performed with simultaneous irradiation and electron microscopy or diffraction.At elevated temperatures, U3Si exhibits the ordered AuCu3 structure. On cooling below 1058 K, the intermetallic transforms, evidently martensitically, to a body-centered tetragonal structure (alternatively, the structure may be described as face-centered tetragonal, which would be fcc except for a 1 pet tetragonal distortion). Mechanical twinning accompanies the transformation; however, diferences between electron diffraction patterns from twinned and non-twinned martensite plates could not be distinguished.

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