Effect of applied stress on precipitation of Guinier-Preston zones in a Cu-0.9 wt.% Be single crystal

A stress-oriented formation of plate-shaped Guinier - Preston (GP) zones in single crystals of a Cu - 0.9 wt.% Be alloy aged at 200 degrees C has been found. A compressive stress applied in the [ 001] direction assists the formation of the GP zones perpendicular to the [ 001] axis, while a tensile stress results in the preferential formation of the GP zones parallel to the stress axis. The applied stress strongly affects the nucleation of the GP zones. Free ageing at 275 degrees C after compressivestress ageing at 200 degrees C produces plate-shaped gamma '' precipitates perpendicular to the stress axis, indicating a continuous change in the structure of the GP zones into that of the gamma '' phase. From length-change measurements during ageing, the misfit strains of the GP zone or gamma '' precipitate in directions parallel and perpendicular to the plate plane are estimated, respectively, as - 0.01 and - 0.10 for the GP zone and - 0.01 and - 0.11 for the gamma '' precipitate.