0000000000459325
AUTHOR
P. Horodek
Use of positron annihilation measurements to detect the defect beneath worn surface of stainless steel 1.4301 (EN) under dry sliding condition
Abstract Positron measurements were performed for detection of the subsurface zone in the stainless steel 1.4301 (EN) exposed to dry sliding. They revealed the defect profile induced by dry sliding which is extended inward the worn surface from 85 μm to 400 μm depending on the applied load during the tribo-test. This result was obtained using the positron techniques, while the microhardness profile exhibited shorter range of the microhardness depth profile, i.e., from 70 μm to 150 μm. However, at the depth of about 5 μm from the worn surface the sudden increase in the microhardness was observed. The complementary measurements of X-ray diffraction and SEM micrographs of the worn surface were…
The slowing down times of positrons emitted from selected β+ isotopes into metals
Abstract We report the GEANT4 Monte Carlo simulations and the approximated calculations of the slowing down time (SDT) for positrons emitted from three β+ isotopes, i.e., 22Na, 68Ge/68Ga and 48V. The first two isotopes are commonly used in the positron annihilation spectroscopy. The results revealed that the SDT exhibits the nonsymmetrical distribution and its average value depends on the end point energy of the isotope, the density and atomic number of the implanted material. For metals the average SDT varies from 0.4 ps to a few ps. We argue that this can affect the analysis of the measured positron lifetime and should be considered in theoretical calculations. The SDT in selected gases w…
Study of the e<sup>+</sup> Distribution in a Layered Stack Sample Using Positron Lifetime Spectroscopy
The results of the Monte Carlo (MC) simulations, using GEANT4 codes, indicate the enhancement of the fraction of the e+ in the denser regions of the sample embedded by the less dense environment. The positron lifetime measurements, performed for two stacks of layers consisting of pure aluminum and silver do not seem to reveal this effect. Some features of the e+ distribution detected in the experiments are not reproduced by the MC simulations.
The positron distribution in a layered stack sample studied with the use of positron lifetime spectroscopy
Abstract Computer simulation using GEANT4 codes indicates an enhancement of the fraction of implanted positrons stopped in the denser regions of a layered sample. However, positron lifetime measurements performed for layers of pure aluminum, silver and gold foils do not reveal this effect, indicating instead that backscattering plays an important role in determining the positron implantation profile in layered and/or heterogeneous samples.
Positron Annihilation Study of Defects Induced by Various Cutting Methods in Stainless Steel Grade 304
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,…
Positron implantation profiles in layered samples
The paper presents theoretical and experimental studies of the positron implantation profiles in layered samples. The Monte Carlo simulations performed using the GEANT4 toolkit reveal accumulation of positrons in the denser layer embedded between two less dense layers. That effect is significant not only for low energy positrons at slow monoenergetic positron beams but also for high energy positrons which are emitted from radioactive nuclei in conventional experiments. Measurements of the positron implantation profile into the samples which consist of silver and aluminium foils of different thickness show profile features which correspond well with those simulated by the GEANT4 toolkit for …
Defects in Martensitic Stainless Steel 1.4031 (EN) Exposed to Friction as Seen by Positron Annihilation
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.
The Distribution of Slowing-Down Times of Positrons Emitted from <sup>22</sup>Na and <sup>68</sup>Ge\<sup>68</sup>Ga Isotopes into Metals
The results of the Monte Carlo simulation, using GEANT4 codes, of the slowing-down time prior to the thermalization in metals for positrons emitted from the 22Na and 68Ge\68Ga sources are presented. Due to the energy spectrum and probabilistic processes accompanying positrons traversing a medium the slowing-down time exhibits a distribution which has a long tail. Nevertheless, the average value of the time is ranged from 0.4 ps to 8 ps depending on the density of the medium as it is for the 22Na positrons. For positrons emitted from the 68Ga nucleus the average value of the slowing-down time increases and it is ranged from 1 ps to 20 ps.