scholarly journals Free volumes in bulk nanocrystalline metals studied by the complementary techniques of positron annihilation and dilatometry

2012 ◽  
Vol 407 (14) ◽  
pp. 2670-2675 ◽  
Author(s):  
Roland Würschum ◽  
Bernd Oberdorfer ◽  
Eva-Maria Steyskal ◽  
Wolfgang Sprengel ◽  
Werner Puff ◽  
...  
Keyword(s):  
Positron Annihilation ◽  
Nanocrystalline Metals ◽  
Complementary Techniques ◽  
Bulk Nanocrystalline

Characterization of H-Plasma Treated ZnO Crystals by Positron Annihilation and Atomic Force Microscopy

2012 ◽  
Vol 331 ◽  
pp. 113-125 ◽  
Author(s):  
Jakub Čížek ◽  
I. Procházka ◽  
J. Kuriplach ◽  
W. Anwand ◽  
Gerhard Brauer ◽  
...  
Keyword(s):  
Atomic Force Microscopy ◽  
Positron Annihilation ◽  
Crystal Surface ◽  
Photon Momentum ◽  
Force Microscopy ◽  
Atomic Force ◽  
Before And After ◽  
Positron Lifetime Spectroscopy ◽  
Complementary Techniques

Nominally undoped, hydrothermally grown ZnO single crystals have been investigated before and after exposure to remote H-plasma. Defect characterization has been made by two complementary techniques of positron annihilation: positron lifetime spectroscopy and coincidence Doppler broadening. The high-momentum parts of the annihilation photon momentum distribution have been calculated from first principles in order to assist in defect identification. The positron annihilation results are supplemented by Atomic Force Microscopy for characterization of the crystal surface. It was found that virgin ZnO crystal contains Zn-vacancies associated with hydrogen. H-plasma treatment causes a significant reduction in concentration of these complexes. Physical mechanism of this effect is discussed in the paper.

The Clustering of Cu Atoms in Neutron Irradiated Reactor Pressure Vessel Steels Studied by Positron Annihilation

2008 ◽  
Vol 273-276 ◽  
pp. 81-86
Author(s):  
Jakub Čížek ◽  
Ivan Procházka ◽  
Jan Kocik
Keyword(s):  
Positron Annihilation ◽  
Pressure Vessel ◽  
Nuclear Power ◽  
Positron Annihilation Spectroscopy ◽  
Reactor Pressure Vessel ◽  
Maximum Diameter ◽  
Pressure Vessel Steels ◽  
Positron Lifetime Spectroscopy ◽  
Complementary Techniques ◽  
Reactor Pressure

Defect studies of neutron-irradiated Cr-Mo-V (VVER-440) type reactor pressure vessel steels were performed in the present work. The steels were irradiated in the nuclear power plant reactor under the conditions of a regular operation. Characterization of the irradiation induced defects was performed by two complementary techniques of positron annihilation spectroscopy: (i) positron lifetime spectroscopy was used for identification of defects and determination of defect densities, (ii) coincidence Doppler broadening was employed for investigation of Cu atom aggregates. Long range diffusion of Cu atoms is assisted by the irradiation induced vacancies. The solute Cu atoms form small clusters in the irradiated steels. Subsequent isochronal annealing of the irradiated steel leads to vacancy assisted clustering of Cu atoms and formation of small precipitates. The Cu clusters exhibit maximum diameter at 400oC. Above this temperature the clusters dissolve again in the matrix.

scholarly journals Processing of Bulk Nanocrystalline Metals at the US Army Research Laboratory

10.3791/56950 ◽  
2018 ◽  
Author(s):  
Vincent H. Hammond ◽  
Billy C. Hornbuckle ◽  
Anit K. Giri ◽  
Anthony J. Roberts ◽  
Thomas L. Luckenbaugh ◽  
...  
Keyword(s):  
Research Laboratory ◽  
Nanocrystalline Metals ◽  
Army Research Laboratory ◽  
Us Army ◽  
The Us ◽  
Bulk Nanocrystalline

scholarly journals An Insight into Machining of Thermally Stable Bulk Nanocrystalline Metals

2018 ◽  
Vol 20 (12) ◽  
pp. 1800405 ◽  
Author(s):  
Vincent H. Hammond ◽  
Thomas L. Luckenbaugh ◽  
Michael Aniska ◽  
David M. Gray ◽  
Joshua A. Smeltzer ◽  
...  
Keyword(s):  
Nanocrystalline Metals ◽  
Thermally Stable ◽  
Bulk Nanocrystalline ◽  
Insight Into

scholarly journals Positron Annihilation Spectroscopy and Small Angle Neutron Scattering Characterization of Nanostructural Features in Irradiated Fe-Cu-Mn Alloys

2000 ◽  
Vol 650 ◽  
Author(s):  
B. D. Wirth ◽  
P. Asoka-Kumar ◽  
R. H. Howell ◽  
G. R. Odette ◽  
P. A. Sterne
Keyword(s):  
Neutron Scattering ◽  
Positron Annihilation ◽  
Small Angle ◽  
Small Angle Neutron Scattering ◽  
Nuclear Reactor ◽  
Positron Annihilation Spectroscopy ◽  
Peak Hardness ◽  
The Matrix ◽  
Complementary Techniques

ABSTRACTRadiation embrittlement of nuclear reactor pressure vessel steels results from a high number density of nanometer sized Cu-Mn-Ni rich precipitates (CRPs) and sub-nanometer matrix features, thought to be vacancy-solute cluster complexes (VSC). However, questions exist regarding both the composition of the precipitates and the defect character and composition of the matrix features. We present results of positron annihilation spectroscopy (PAS) and small angle neutron scattering (SANS) characterization of irradiated and thermally aged Fe-Cu and Fe-Cu-Mn alloys. These complementary techniques provide insight into the composition and character of both types of nanoscale features. The SANS measurements indicate populations of CRPs and VSCs in both alloys. The CRPs are coarser in the Fe-Cu alloy and the number densities of CRP and VSC increase with the addition of Mn. The PAS involved measuring both the positron lifetimes and the Doppler broadened annihilation spectra in the high momentum region to provide elemental sensitivity at the annihilation site. The spectra in Fe-Cu-Mn specimens thermally aged to peak hardness at 450°C and irradiated at 288°C are nearly identical to elemental Cu. Positron lifetime and spectrum measurements in Fe-Cu specimens irradiated at 288°C clearly show the existence of long lifetime (∼500 ps) open volume defects, which also contain Cu. Thus the SANS and PAS provide a self-consistent picture of nanostructures composed of CRPs and VSCs and tend to discount high Fe concentrations in the CRPs.

scholarly journals Deformation twinning in bulk nanocrystalline metals: Experimental observations

JOM ◽  
2008 ◽  
Vol 60 (9) ◽  
pp. 60-64 ◽  
Author(s):  
Y. T. Zhu ◽  
X. Z. Liao ◽  
X. L. Wu
Keyword(s):  
Deformation Twinning ◽  
Nanocrystalline Metals ◽  
Bulk Nanocrystalline

scholarly journals Strategy for Electrodeposition of Highly Ductile Bulk Nanocrystalline Metals with a Face-Centered Cubic Structure

2014 ◽  
Vol 55 (12) ◽  
pp. 1859-1866 ◽  
Author(s):  
Isao Matsui ◽  
Yorinobu Takigawa ◽  
Daisaku Yokoe ◽  
Takeharu Kato ◽  
Tokuteru Uesugi ◽  
...  
Keyword(s):  
Face Centered Cubic ◽  
Nanocrystalline Metals ◽  
Cubic Structure ◽  
Face Centered ◽  
Bulk Nanocrystalline
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