Precipitation and growth of the metastable phase gamma ' in Al-1 at.% Ag under cyclic deformation at elevated temperatures

During heavy plastic deformation, precipitates of the metastable gamma' pha se nucleate in large amount. Because of a high density of moving dislocatio ns in cyclically deformed crystals, nucleation and morphology differ from t hose of thermal gamma', whereas crystallographic structures and growth mech anisms are equivalent. The resulting tiny plate-like particles display a hi ghly symmetrical hexagonal shape. Their aspect ratio (length-to-width ratio ) is small compared with that of thermally grown gamma' precipitates. Under cyclic deformation nucleation of gamma' at the interface of Guinier-Presto n zones is observed. This may be the case for thermal gamma' too, which in the past was believed to form directly from the matrix.