Papers by Keyword: Positron Lifetime Technique

Abstract: Positron annihilation lifetime (PAL) , electrical and mechanical techniques have been used to study the thermal vacancies in one of the most important engineering aluminum alloys which is 2024 alloy. Quenching experiments were usually performed on thin specimens to ensure a uniform quenching rate throughout the specimen. The specimens were prepared with dimensions of 0.15 × 1.5 × 1.5cm³. After grinding, polishing and etching, samples of 2024 were homogenized for 12 h at 673 K and annealed for 90-min., before quenched in water (277 K) and then subject to positron lifetime, electrical and mechanical for measurements. From such measurements it is possible to deduce the vacancy formation enthalpy, which in combination with the results of self-diffusion measurements, give a value for migration enthalpy of the vacancy. These are very important quantities in the study of the annealing of irradiation induced defects.

Abstract: 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.

Abstract: A comprehensive and systematic study using PALS technique, Vickers hardness test and electrical LCR meter were undertaken to follow property development during the recently promoted interrupted ageing treatment for 2024 aluminum alloy. In this work, solution heat treatments at different temperatures were performed in aircraft materials 2024 aluminum alloy. This work describes the development of the dependence of mechanical, electrical properties of 2024 Al-alloys on heat treatment to characterize microstructural changes during heat treatment. PALS, mechanical and electrical testing will be used to measure the features of the material as a function of time for each ageing temperatures.

Abstract: Positron annihilation lifetime (PAL) measurement is one of the most important nuclear techniques used in materials science. Electrical measurements are also used in materials science. Both PAL and electrical measurements were used here to determine the activation energy of migration of dislocations in one of the most important engineering aluminum alloys: 2024. Samples of 25% deformed (thickness reduction) material have been used for these studies. The isothermal annealing measurements were performed at 583, 603, 623 and 643K for both techniques. The activation energy of migration of the dislocation was found to be equal to 1.24 ± 0.08eV by using PAL measurements and to 1.35 ± 0.01eV by using the electrical technique.

Abstract: 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.