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

摘要

A stress-oriented formation of plate-shaped Guinier-Preston (GP) zones in single crystals of a Cu-0.9 wt. percent Be alloy aged at 200 deg 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 deg C after compressive-stress ageing at 200 deg 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.