This work addresses the process of ageing in Al-4wt.% Cu at two temperatures (150 °C, 180°C) and in conditions of secondary ageing at temperatures up to 60°C, after artificial ageing treatment at 150°C. Positron lifetime and coincidence Doppler broadening measurements are reported. The analysis shows an initial association of positron trapping sites with Cu (about 9 at. % Cu at the annihilation site) that decreases to 7˜6 % in the initial stages of ageing, but then increases sharply (up to 25 at. % Cu after 300 hours at 180°C). The positron lifetime also displays an initial decrease followed by a final increase. The results confirm the hypothesis that positrons are not trapped in GP zones, but show that trapping occurs in GP zones formed at 150°C. During secondary ageing, the vacancy-Cu association as well as the positron lifetime decrease with the ageing time. This is attributed to the formation of GP zones due to residual supersaturation.
|Titolo:||Positron Spectroscopy Analysis of Vacancy-Solute Nanoaggregates in Al-Cu|
|Data di pubblicazione:||2004|
|Appare nelle tipologie:||01.1 Articolo in Rivista|
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|Ferragut et al MatSciForum 2004.pdf||PDF editoriale||Accesso riservato|