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Electrical Resistivity and Positron Lifetime Studies of Precipitation Effects in Al-Cu Alloy

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Αda P., Cieslar M., Vostrý P., Bečvář F., Νovotný I., Procházka I.

Acta Physica Polonica A

1995

vol. 88

issue 1

111-117

Decomposition of the supersaturated solid solution of 2 at.% Cu in Al was investigated by means of electrical resistivity and high-resolution positron lifetime measurements. The phase composition of this alloy was determined by transmission electron microscopy. Electrical resistivity measurements were performed by a classical four-point method. Positron lifetime spectra were measured by means of a spectrometer consisting of two BaF_{2} detectors and a standard fast-slow coincidence system. The specimens were first exposed to the solution heat treatment at 783 K for 19 hours with a subsequent quenching. Then the specimens were isochronally annealed in the temperature range 293 ÷ 573 K. Annealing responses of electrical resistivity and positron annihilation were studied. Resistivity measurements as well as transmission electron microscopy observations confirmed the well-known decomposition sequence of the Al-Cu alloy. The decomposition of the alloy was manifested by the decrease in the intensity of positron lifetime component τ_{2} = (207 ±2 ) ps correlated with simultaneous appearance and increase in the intensity of τ_{3} = (180 ± 5) ps component. Component τ_{2} originates from positron annihilation in vacancies trapped at the Guinier-Preston zones while τ_{3} comes from annihilation of the positrons localized in the misfit dislocations at coherent precipitates of the Al_{2}Cu phase. The shortest observed component τ_{1} apparently belongs to annihilation of untrapped positrons.

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1 Acta Physica Polonica A

1 1995

1 Bečvář F.

1 Cieslar M.

1 Procházka I.

1 Vostrý P.

1 Αda P.

1 Νovotný I.

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Electrical Resistivity and Positron Lifetime Studies of Precipitation Effects in Al-Cu Alloy