At higher aging times (60 and 120 min), both τ av and H v decreased with increasing aging temperature. The results revealed that the average life time, τ av, and hardness, H v, continuously increased with increasing aging temperature at lower aging times (15 and 30 min). All of the samples were then characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis as well as by hardness tests. Samples of Al-5wt% Si alloy were treated with a T6 heat treatment, that is, solution treatment at 550☌ for 2 h, quenching in cold water at 0☌, followed by aging at different temperatures for various periods of time. The present study aimed to investigate the influence of heat treatment on the microstructure and mechanical properties of Al-5wt% Si alloy by positron annihilation spectroscopy and Vickers microhardness measurements. These results are discussed on the basis of the free volume model. The back increase in the electron curve seems to be absent in the case of gamma irradiation. Meanwhile, after electron irradiation, the intensity of the o-Ps lifetime component as the dose increases exhibits two diierent regions may be identiÿed as a rapid drop, followed by a smooth increase, then, it levels oo and remains constant. In contrast, the intensity of the o-Ps component, I3, decreases with the dose, up to about 540 kGy, followed by a much smooth decrease up to 1200 kGy then it levels oo up to 1500 kGy. After gamma irradiation no detectable changes are observed in the o-Ps lifetime. The observed lifetime spectra were resolved into three components and the ortho-positronium (o-Ps) lifetime component was associated with the pick-oo annihilation of positronium trapped by the free volume. The samples were irradiated at room temperature with doses ranging from 30 up to 1500 kGy. X-ray diiraction proÿles for non-irradiated and irradiated conducting polystyrene are performed to investigate the structural nature of the samples. The eeects of electron beam and gamma irradiation on microscopic structure of a conducting polystyrene (polystyrene + 15% carbon black) have been studied using positron annihilation lifetime spectroscopy.
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