E. Gomaa

A study on commercial pure Al (1050) after cold rolling at room temperature with various deformations using positron annihilation

Positron annihilation lifetime (PAL), Doppler broadening (DB), and Vickers microhardness measurements (Hv) were performed to study the isochronal annealing of commercial pure Al (1050) in the temperature range from room temperature (RT) to 823 K after cold rolling at RT with various deformations of 16%, 37%, and 54%. PAL measurements show a decrease in the average lifetime of positron (τav) followed by saturation at 190 ps as a function of annealing temperature. The results of Doppler broadening of annihilation radiation (S and W parameters) are found to be consistent with PAL measurements. The correlation between the characteristics of positron annihilation and Hv shows three annealing stages of microstructure in commercial Al, which are attributed to recovery, partial recrystallization, and complete recrystallization.

Application of Positron Annihilation Spectroscopy to Study the Recovery of Commercial Pure Al and Al-0.96 wt.% Si Alloys

Isochronal annealing of quenched commercial pure Al (99.95%) and Al-0.96 wt.% Si was investigated between room temperature (RT) and 550 °C. The annealing of defects was studied using positron lifetime and Doppler broadening (DB) techniques. The retardation of annealing defects in the two alloys is interpreted in terms of precipitation of impurities and Si atoms, as well as defect properties (size and concentration) in the framework of the two state trapping model.

Correlation between free-volume parameters and physical properties of polyethylene-nitrile rubber blend

Positron annihilation lifetime spectroscopy (PALS) was used to study the immiscibility of a polar nitrile rubber (NBR) that had been blended with pure and waste, low- and high-density polyethylene (PE). The effect of the weight percent of the rubber added to the PE was also investigated. It was found that a complicated variation (positive and negative) in both free-volume parameters (τ3 and I3) from the values of the initial polymers forms an immiscible blend. These results are supported by a significant broadening in the free-volume hole size distributions. This has been interpreted in terms of interfacial spaces created between the boundaries of the two phases. Furthermore, a correlation was established between the free-volume parameters (τ3 and I3) and the electrical and mechanical properties of the before mentioned polymer blends as a function of the weight percent of waste PE.

Correlation of Mechanical Properties with Defect Structure in Commercial Pure Al and Al-Mn Alloys Studied by Positron Annihilation Spectroscopy

The variations during isochronal annealing of cold-rolled commercial pure Al (1050) and Al-Mn (3004) has been investigated between room temperature (RT) and 823 K. The annealing stages have been identified as recovery, partial recrystallization, complete recrystallization and grain growth using positron annihilation lifetime (PAL) spectroscopy, Doppler broadening of annihilation radiation (DBAR) spectroscopy and Vickers microhardness (Hv) measurements. The retardation of complete recovery in Al-Mn alloys is due to the presence of vacancy-Mn complexes. A positive correlation has been found between positron annihilation parameters (τav & Snor) and mechanical properties (Hv) for the two alloys under investigation.