Jerzy Dryzek

Positron annihilation studies of subsurface zones incopper

This paper presents the results of positron annihilation studiesof defect profiles in well-annealed copper samples whosesurfaces were exposed to wear and friction processes. The defectprofiles exhibited exponential decay. The dependence of thedefect distribution behavior on the load, duration of the pin-on-disc test, the temperature of the sample and the velocity ofthe ball were studied. The defect profile induced bytribotesting was compared with its analogues in samplessubjected to cutting or compression.

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, i.e., 40 μm. The laser cut machining generates the zone with the lowest concentration of defects which does not vary with the depth. However, LC affects the sample up to the depth of about 500 μm. The degree of the surface roughness is similar for laser cut and AWJ, but for the MC it is five times smaller.

Migration of vacancies in stainless steel measured by positron annihilation

Abstract The results of Doppler broadening studies of annealing processes in the commercial stainless steel are presented. Two stages were established in the temperature dependence of the S -parameter. The first one corresponds to the steep decrease of the S parameter in the temperature range from room temperature up to 500°C and reflects annealing of defects introduced during the manufacture process. Three models of vacancy sinking and migration were considered. Taking into account diffusion of vacancies to the surface as well as to the grain boundaries gave the activation energy of vacancy diffusion equal to 1.215 ± 0.016 eV. The increase and consequent decrease of the S -parameter in the temperature range from 600°C up to 1060°C in the second stage is considered as caused by the precipitation of the carbide M 23 C 6 .

Subsurface zone studied by positron lifetime measurements

Measurements of the positron lifetime in the subsurface zones of copper samples are presented. The samples were slid against a graphite cylinder and the measurements performed just at the first stages of the creation of the subsurface zone. From the positron lifetime we were able to deduce the shear stress in this zone. The depth profile of the subsurface zone measured by positron annihilation exhibited different types of open volume defects in well-annealed samples. The depth profile was not observed when imperfections were present in the samples.

Subsurface Zones Created Under Lubrication Conditions Studied by Positron Annihilation

We present positron annihilation studies of the subsurface zones induced in the sliding contact of two metals under lubrication conditions. The surfaces of copper samples were exposed to the sliding of a small steel ball and the open volume defects induced under the surface were detected using both a positron beam experiment and a conventional positron experiment. From our studies we deduced that the total range of subsurface zones was almost independent of the lubrication conditions. For the highest load of the ball we observed that the subsurface zone created under lubrication condition extends deeper than for the case where the zone was induced in the dry sliding contact. We found that sliding with lubricant induces a layer on the surface whose properties, as detected by positrons, were different than those of other samples. It seems that this layer could contain open volume defects that are larger than those in deeper layers. Our studies have shown that the positron beam technique is a suitable tool for defect characterization in tribotested samples.

Determination of free-electron parameters of thin films

Abstract Relations for the optical transmission and reflection coefficients expressed in terms of electron transport parameters are presented. The effects of various parameters on transmission and reflection in free-electron metallic films are investigated. It is found that the ratio of the electron mean free path to the film thickness, the plasma frequency and the parameter S describing interband transitions and core electrons can be determined with reasonable accuracy from the optical data. A combined analysis of optical and electrical data enables the scattering parameter p to be determined. This method is used to analyse experimental data for r.f. sputtered gold and silver films.

Study of the Mg-Cd system by positron annihilation methods

The problem of preferential positron annihilation in binary alloys has not been satisfactorily solved in the past. We examine this effect experimentally in Mg-Cd alloys using the new technique of Doppler broadening measurements with background reduction which allows us to observe positron annihilation with core electrons. Conventional positron lifetime spectroscopy is applied as well. We measure the Doppler spectra and positron lifetimes for selected alloys in the whole concentration range of the Mg-Cd system. The analysis of experimental results is supported by theoretical calculations. The conclusion is given that a small positron preferential annihilation occurs at Mg sites. Besides, the temperature dependencies of the peak counting rate of the angular correlation curve are measured for several samples and the vacancy formation energies are established. In the case of Mg-20 at.% Cd alloy, the increase of the peak counting rate characteristic for generation of thermal vacancies shows a discontinuity close to the order-disorder transition temperature.

DIFFERENCES BETWEEN CRYSTALLIZATION OF LDPE AND IPP IN EPDM MATRIX

Supermolecular structure of blends made of low density polyethylene (LDPE) or isotactic polypropylene (iPP) and ethylene-propylene- diene rubber (EPDM) was studied with X-ray diffraction (WAXS and SAXS), differential scanning calorimetry (DSC) and positron annihilation spectroscopy. Experimental data reveals different behaviour of the plastomers in the elastomer matrix. The crystalline phase of LDPE is to some extent solvated by the amorphous EPDM, whereas addition of iPP enhances the degree of the blends crystallinity. This additional crystalline phase is of imperfect nature and probably originates from cocrystallization of propylene monomer units from EPDM onto iPP particles. LDPE recrystallizes in the blends with EPDM at a lower temperature, the higher the plastomer content. Contrary to this, iPP recrystallizes in the rubber matrix at higher temperature. The blends composition influences the morphology of the crystalline phase. Interlamellar amorphous layer thickness slightly increases with an increase of LDPE content, being simultaneously accompanied by a slight decrease of the crystalline lamella thickness. The long period values remain practically constant. In the case of iPP/EPDM blends, the crystalline lamella thickness increases with an increase of the plastomer content, whereas the interlamellar amorphous layer remains constant, which results in an increase of the long period. The reversed tendency, observed for high-filled samples containing ⩾ 50 phr of iPP, is likely to be associated with too many nucleation centres, finally reducing the spherulite size. Despite annihilation taking place in the amorphous as well as the crystalline phase of polymers, the positron lifetime data stays in good agreement with the postulated supermolecular structure of the blends.

Study of subsurface zones induced by friction and wear using positron annihilation method

Abstract The positron annihilation studies of defect profiles in well annealed gold and copper samples whose surfaces were exposed to the friction and wear processes are presented. In the case of copper samples the defect profile was obtained by etching the layers and measuring the lineshape parameter of annihilation radiation. The defect profile detected in such a case exhibited the exponential decay dependence. For gold samples the concentration of defects in the near surface laying region were obtained using the monoenergetic positrons. Close to the surface the defect concentration is an order 10−4 and the type of the defects as positron traps did not change with the depth.

Positron Absorption Studies in Electrodeposited Copper Layers

Positron annihilation studies within the standard methods in copper layers electrodeposited on the copper substrate are presented. The main interest was focused on the studies of the S-parameter evaluated from the annihilation line as a function of the thickness of the covered layer. The thickness of the layer ranged from 5 to 250 μm and we were interested in the fraction of positrons absorbed in it. From that we tested two relations linking the local and the measured positron annihilation characteristics, and the positron implantation profile. The reasonable description of the experimental data was obtained when the fraction of positrons implanted in the layer was deduced from the exponential positrons profile averaged over a solid angle. The experimental studies have been performed with 22 Na and 68 Ge positron sources. The present considerations could be dedicated to positron studies of inhomogeneous solids.