The sequence of precipitation in Cu-2w/0 Be alloys
Abstract
We present herein a summary of the morphologies and TEM diffraction effects of the several metastable phases observed when a supersaturated Cu-2w/0 Be alloy decomposes at temperatures ranging from 500°C (773 K) to room temperature. These observations are correlated with previously recorded ones and a consistent nomenclature of the metastable phases is given. A metastable equiaxed phase has been found to form prior to the well-known plate-like G.P. zones. Also the sequence of precipitation is recorded as a function of temperature and quenching method. The results are discussed in terms of nucleation theory.
Résumé
Nous présentons ici un résumé des morphologies et des effets de diffraction électronique des diverses phases métastables que l'on observe lorsqu'un alliage Cu-2% Be sursaturé se décompose entre 500°C (773 K) et la température ambiante. Nous comparons nos observations avec celles qui ont été publiées antérieurement, et nous proposons une nomenclature cohérente des phases métastables. Nous avons mis en évidence la formation d'une phase metastable équiaxe, antérieure aux zones GP en plaquettes bien connues. Nous analysons également la suite des précipitations en fonction de la température et de la méthode de trempe. Nous discutons des résultats à partir de la théorie de la germination.
Zusammenfassung
Wir fassen hier die Formen und die Effekte verschiedener metastabiler Phasen, die während des Zerfalles einer übersättigten Cu-2 Gew.-% Be-Legierung zwischen 500°C (773 K) und Raumtemperatur auftreten, auf die Elektronenbeugung zusammen. Die Beobachtungen werden mit früheren verglichen; eine konsistente Bezeichnung der metastabilen Phasen wird angegeben. Es wurde gefunden, daβ sich eine gleichachsige metastabile Phase vor der wohlbekannten plattenförmigen Guinier-Preston-Ausscheidung bildet. Auβerdem wird die Folge der Ausscheidungsbildung in Abhängigkeit von Temperatur und Abschreckmethode angegeben. Die Ergebnisse werden mit der Keimbildungstheorie diskutiert.
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