Emad A. Badawi

Effect of sample thickness on the measured mass attenuation coefficients of some compounds and elements for 59.54, 661.6 and 1332.5 keV γ-rays

Abstract Measurements have been made to determine γ-rays attenuation coefficients very accurately by using an extremely narrow-collimated-beam transmission method. The effect of the sample thickness on the measured values of the mass attenuation coefficients (μ/ρ) cm 2 / g of perspex, bakelite, paraffin, Al, Cu, Pb and Hg have been investigated at three different γ-ray energies (59.54, 661.6 and 1332.5 keV). It is seen that for these chosen materials ( μ / ρ ) remains constant in good agreement with the theoretical values up to 3 mean free paths and after that ( μ / ρ ) values for Cu, Pb and Hg decrease with further increase in the absorber thickness. This result may be attributed to the increase in the number of coherent small-angle scattering photons which reach the detector.

Investigation of defects (migration and formation) in metals by positron annihilation lifetime

Abstract In the present work a discussion of the possibilities to study defect in solids is presented. Generally, positron behavior in metals is simpler than in insulators. Migrations and formations of defects (point defects, dislocation) in metals have been studied in detail by using positron annihilation lifetime technique. Samples of Pb, Bi, Al, Mg, Ag, and Cu were deformed to 20% thickness reduction then annealed at different temperature 1 h before quenched (air cooling). In each pair of samples, lifetime spectrum was accumulated, as a function of the annealing temperature and measured at room temperature. For each metal, two stages were observed with a minimum at T=(0.52–0.62)Tm. This seems to be due to the compensation of two different processes; one for recovery and the other for defect formation. This observation of two processes is clear only on the metals have face center cubic structure such as (Al, Pb, Ag and Cu).

Detecting Defects In Aircraft Materials By Nuclear Technique (Pas)

Positron annihilation spectroscopy (PAS) is one of the nuclear techniques used in material science. The present measurements are used to study the behavior of defect concentration in one of the most important materials aluminum alloys which is the 7075 alloy. It has been shown that positrons can become trapped at imperfect locations in solids and their mean lifetime can be influenced by changes in the concentration of such defects. No changes have been observed in the mean lifetime values after the saturation of defect concentration. The mean lifetime and trapping rates are studied for samples deformed up to 58.3%. The concentration of defect range vary from 1015 to 1018cm-3 at the thickness reduction from 2.3 to 58.3%. The dislocation density varies from 108 to 1011cm/cm3.

POSITRON ANNIHILATION AND XRD FOR DETECTING Al ALLOYS (50XX)

The positron annihilation parameter (mean lifetime) increases with increasing Mg contents for annealed and quenched samples (50XX). Positron parameter τ, s (Doppler broadening) increase with increasing Q.T for the same (50XX). The preferred orientation is one of the most important parameters that can be observed by XRD for materials, for such measurements in our observation: the dependence of the preferred orientation on the Mg content, the dependence of the preferred orientation on the Q.T, and the dependence of the preferred orientation on the degree of deformation.

Vacancy Migration and Formation in A356.0 Aluminum Casting Alloys by Positron Annihilation Technique

The migration and formation curves for the A365.0 (Al-7% Si-0.4Mg) casting alloys are investigated by positron lifetime (PL) and S-parameter measurements from room Temperature (RT) to 873 K. The observed dependence of PL and S-parameter on quenching temperature (QT) is attributed to vacancy formation. PL results were analyzed applying the two state trapping model and the formation enthalpy H v f 1 was estimated by using different methods. Introduction The phenomenon of positron annihilation has been utilized in solid state physics research to probe a variety of materials. This technique has become established as a useful tool and is successfully applied for the investigation of defect structures in various materials including technologically important materials. The positron annihilation technique (PAT) is shown to be a sensitive nondestructive tool in the study of defects in solids. The advantage of PAT is its ability to distinguish different types of defects such as vacancies, vacancy clusters, dislocations, grain boundaries, voids, etc. Experimental The composition of the casting Al-Si alloy used in the present investigation is given in Table 1. Table 1. The composition of the casting Al-Si alloy used in the present work in wt. % Al-alloy Si Fe Cu Mn Mg Zn A356.0 7.0 0.2 0.2 0.1 0.3 0.1 Preparation, dimensions and polishing of the samples are described in [1,2]. Positron lifetime studies were performed at RT using a fast-fast coincidence system with a time resolution of about 281 ps (FWHM) which is described elsewhere [3,4]. Doppler broadening (D. B.), S-parameters were measured with an Ortec HPGe detector having an energy resolution 1.95 keV for the 1.33 MeV line of 60 Co[5]. Each positron lifetime spectrum was measured for 9×10 3 s and about 1.2×10 3 coincident events at the peak were accumulated. The lifetime spectra were analyzed using the program POSITRONFIT [6]. The spectra were satisfactorily analyzed as a single lifetime component after subtraction of the background and source component. Results and Discussion Migration of Thermal Defects in (A356.0) The lifetime spectra were resolved into exponential terms via least-squares fitting. The long lifetime is due to annihilation in the source while the short lifetime is a mixture of the lifetime components from bulk lattice, vacancy and grain boundaries. Mean lifetime reflects the characteristics of the defect formation and recovery processes and is a function of the quenching temperature (Q.T). All the samples were homogenized for 10 h at 823 K for the lifetime and D.B Materials Science Forum Online: 2004-01-15 ISSN: 1662-9752, Vols. 445-446, pp 45-47 doi:10.4028/www.scientific.net/MSF.445-446.45

Artificial Ageing Effect on Mechanical, Electrical Properties and Positron Lifetime of Aircraft 2024 Alloy

Heat Treatments for Different Aging Times Were Performed on 2024 Aluminum Alloy. the Effect on the Positron Lifetime, Electrical and Mechanical Properties of the 2024 (Al-Cu-Mg) Alloy Was Studied. Artificial Ageing Was Conducted by Heating at a Constant Rate to a Specific Temperature, Followed by Annealing. the Alloy Was Treated at 192°C for Various Times, Followed by Annealing. Measurements as a Function of Aging Time Were Found to Exhibit Prominent Changes Related to the Formation of Precipitates.

Positron Annihilation & Micro-Hardness Measurement of 6063 and 6066 with Compromise with Ingot Al

The aim of this work was to study the resistance of this type of alloy to quenching. Hardness measurements can be defined as macro-, micro- or nano- scale, according to the forces applied and the displacements obtained. This effect can also be studied using a nuclear, (PALT): positron annihilation lifetime, technique [1]. Microhardness is the hardness of a material, as determined by forcing an indenter such as a Vickers or Knoop indenter into the surface of the material under a 15 to 1000gf load; the indentations are usually so small that they must be measured using a microscope. These samples were quenched at different temperatures ranging from 50 to 500oC. We studied the effect of the quenching temperature upon the hardness measurements. We also studied this variation via the positron annihilation (lifetime) parameter. It is clear from the Vickers hardness that 1050 has the lowest value of Hv, while 6063 is higher and 6066 has the highest values of Hv. Also we could observe ( recognize) that the Hv (number) is reduce as a function of temperature (6066) but for (1050) and (6063) there is no observation of a variation in Hv (number) as a function of quenching temperature. The same observation was also made for 1050, 6063 and 6066 via the lifetime measurements. Here, 6063, 6066 give higher values than 1050. It is clear that the data from both techniques (positron annihilation lifetime and Vickers hardness) for 1050 ingot Al gives lower values of both parameters for Hv and lifetime technique. While Hv for 6066 is higher than the values of 6063 alloy at the same quenching temperature. Using the lifetime technique, one cannot distinguish between the 6063 and 6066 alloys. The applied force has no real effect upon the levels of the hardness values. Also, alloys 6066 and 6063 were defined as heat-treatable alloys but 1050 is not a heat-treatable alloy. The Hv of the 1050 is not affected by the changes in quenching temperature. Alloy 6066 heat-treatable alloy is more affected by the heat treatment than is 6063 alloy, and this is related to the structure of the precipitates in these alloys since 6066 alloy has much more Si and Mg than does the 6063 alloy. The Hv values vary from 14 to 23.9 for 6063 alloy and from 15.7 to 69.8 for 6066 alloy; in comparison with ingot alloy (1050) where it varies from 10.4 to 18.6.

Activation Enthalpy of Dislocation Migration in Aircraft (Aerospace) (2024) Alloy by Positron Spectroscopy

Positron annihilation lifetime is one of the most important nuclear techniques, used to study the isochronal and isothermal annealing in one of the most important engineering aluminum alloys which is 2024 alloy. Samples of 25 % deformation have been used for these studies. Two recovery stages during the isochronal annealing [1] were observed which were ascribed to the recovery of point defects and dislocations introduced by the deformation. The isothermal annealing measurements were performed at 583, 603, 623 and 643 K from which the activation energy obtained was 1.24 ± 0.08 eV.

Defect Investigation of Plastically Deformed Al 5454 Wrought Alloy Using PADBS and Electrical Measurements

Positron Annihilation Doppler Broadening Spectroscopy (PADPS) is a nondestructive technique used in materials science. Electrical measurements are one of the oldest techniques also used in materials science. This paper aims to discuss the availability of using both PADPS and electrical measurements as diagnostic techniques to detect defects in a set of plastically deformed 5454 wrought aluminum alloys. The results of the positron annihilation measurements and the electrical measurements were analyzed in terms of the two-state trapping model. This model can be used to investigate both the defect and dislocation densities of the samples under investigation. Results obtained by both nuclear and electrical techniques have been reported.

Study the Effect of Plastic Deformation in 8006 Al-Alloys by Positron Lifetime Spectroscopy, Vickers Hardness and X-Ray Diffraction

Due to the great effect of defects on the properties of the material including strength, ductility, resistivity and opacity, there are many techniques that are used in defect detecting. Positron annihilation spectroscopy (PAS), Vickers hardness, and X-ray diffraction were used to study the influence of plastic deformation on the properties of 8006 Al-alloy in this work. An increase in the positron lifetime and Vickers hardness with a bit Broadening of XRD peaks was observed with increasing the degree of deformation reflecting a large dislocation density produced by plastic deformation.