Search results for " ANN"
showing 10 items of 1343 documents
Defects in Martensitic Stainless Steel 1.4031 (EN) Exposed to Friction as Seen by Positron Annihilation
2010
We present experimental results of measurements of the Doppler broadening of annihilation line and positron annihilation lifetimes in martensitic stainless steel 1.4031 (EN) samples exposed to the dry sliding under different loads. In particular, we tested the subsurface zone under the worn surfaces. As a main result, we obtained information about the defect profiles in this zone and the total extent of the damage region induced by the dry sliding.
Porphyrin Antenna-Enriched BODIPY–Thiophene Copolymer for Efficient Solar Cells
2018
International audience; Low bandgap A−π–D copolymer, P(BdP-DEHT), consisting of alternating BOronDIPYrromethene (BODIPY) and thiophene units bridged by ethynyl linkers, and its porphyrin-enriched analogue, P(BdP/Por-DEHT), were prepared, and their optical and electrochemical properties were studied. P(BdP-DEHT) exhibits strong absorption in the 500–800 nm range with an optical bandgap of 1.74 eV. On the basis of cyclic voltammetry, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels are evaluated to be −5.40 and −3.66 eV, respectively. After the anchoring of zinc(II) porphyrin on the BODIPY unit, P(BdP/Por-DEHT) displays broadened absor…
Recrystallization in subsurface zone seen by positron annihilation
2010
Abstract The paper presents studies of the defect distribution, detected by the positron annihilation method in the subsurface zone (SZ) of copper samples after dry sliding wear. It takes advantage of a new experimental technique based on scanning of the positron implantation profile. It allowed us to detect the defect profile in copper to the depth of 200 μm in a nondestructive way and study isochronal annealing behavior of this profile. We determined that annealing induces a recrystallization process which runs faster close to the surface than in deeper regions. After sliding, the complete recrystallization of the substructure takes place at temperature c.a. 600 °C. Some changes in the de…
Melting Process of the Sn-45 wt.% In and Sn-77 wt.% In Alloys as Viewed by Positron Annihilation
2006
The temperature dependences of the positron annihilation parameters F and R were determined for Sn–45 wt.% In and Sn–77 wt.% In alloys. The obtained results enabled to verify the vacancy and the quasicrystalline models of the melting process. It was found that for metals transforming into the liquid state from the structures different than the close packed structure, the melting transition are hardly explainable in terms of the vacancy model of melting. The strong trapping of positrons in metallic liquids is an indication of the presence of microvoids (vacancy clusters) or microcrystals containing defects more immense than vacancies. The share of these positron trapping centers in the volum…
Inverse simulated annealing: Improvements and application to amorphous InSb
2014
An improved inverse simulated annealing method is presented to determine the structure of complex disordered systems from first principles in agreement with available experimental data or desired predetermined target properties. The effectiveness of this method is demonstrated by revisiting the structure of amorphous InSb. The resulting network is mostly tetrahedral and in excellent agreement with available experimental data.
Positron Annihilation Study of Defects Induced by Various Cutting Methods in Stainless Steel Grade 304
2011
We report in this article the comparison of the subsurface zones (SZs) in austenitic stainless steel 304 samples created by three cutting techniques, i.e., the laser cutting (LC), abrasive water jet (AWJ), and traditional milling cutting (MC). The crystal lattice defects distribution in this zone were investigated using the positron annihilation method. It was shown that the MC creates the great number mainly edge dislocations decorated by vacancies. Their concentration decreases with the increase of the depth from the cut surface. The total depth of the SZ is extended up to 150 μm from the cut surface. Similar dependency was observed for the AWJ machining but the total depth is much lower,…
Application of Positron Annihilation Spectroscopy to Studies of Subsurface Zones Induced by Wear in Magnesium and Its Alloy AZ31
2011
Interaction of sliding bodies is an important aspect of numerous applications and subject of many studies (Solecki, 1989). Generally, when two surfaces are loaded together the true contact area is much smaller than the apparent one. The true contact is only at high points or asperities of the surfaces where the interactions in the atomic scale take place. Relative movement between the surfaces leads to friction and wear processes. The rate of wear is controlled by the load, the relative velocity and the behaviour of the material near asperities. The region of asperities can be plastically deformed and the stress is transported to the deeper laying region that becomes elastically deformed (F…
'Cold' crystallization in nanostructurized 80GeSe2-20Ga2Se3 glass
2015
International audience; 'Cold' crystallization in 80GeSe 2-20Ga 2 Se 3 chalcogenide glass nanostructurized due to thermal annealing at 380°C for 10, 25, 50, 80, and 100 h are probed with X-ray diffraction, atomic force, and scanning electron microscopy, as well as positron annihilation spectroscopy performed in positron annihilation lifetime and Doppler broadening of annihilation line modes. It is shown that changes in defect-related component in the fit of experimental positron lifetime spectra for nanocrystallized glasses testify in favor of structural fragmentation of larger free-volume entities into smaller ones. Nanocrystallites of Ga 2 Se 3 and/or GeGa 4 Se 8 phases and prevalent GeSe…
Measurements of Positrons Lifetimes in Corroded Nickel
1999
It is over twenty years now that the nuclear method of conducting investigations into defects in the volume and on the surface of solids, based on positron annihilation phenomenon, has been developing on a quite intensive scale [1-3]. The present work is an attempt at adopting positron annihilation to investigations of the phenomenon of pitting corrosion in metals. Pitting occurs mainly in environments containing chlorides and affects metals and alloys covered with passivating oxide layers. Research carried out for many years by the use of various methods . has proved that pittings, which could — after some time — take sizes as large as the tenth of the millimeter order, are formed in the p…
Temperature- and illumination-induced charge-state change in divacancies of GaTe
2010
Temperature-dependent positron annihilation lifetime spectroscopy measurements have been performed in GaTe samples, with and without illumination. The average lifetime shows a monotonous temperature evolution but the lifetime decomposition shows a rich behavior. It is produced by two types of vacancy defects. The vacancy-type defects characterized by their shorter lifetime change their charge state below 100 K and when illuminating with light of an energy of 0.8 eV.