Investigation of precipitation hardening in Cu-2Be-0.2Co by Vickers microhardness and electrical resistance

Abstract

Samples of the commercial alloy Cu-2Be were aged at 325, 280, 250, and 230°C in a high purity helium atmosphere. Vickers micro hardness testing was carried out taking advantage of the fact that in the case of this very fine grained alloy the microhardness is almost independent of load. It is shown that a precise microhardness measurement when combined with an electrical resistance measurement is highly suitable for investigations of the GP zone stage and the γ′ phase. Isotherms of microhardness indicate the beginning of growth of the γ′ phase by a marked steepening of their slopes. The maximum hardness can be taken as a measure of the completion of the hardening process. Isotherms of the change in electrical resistance show two other significant points: the resistance maximum which records the GP zone density, and thereafter the intersection of the resistance curve with the abscissa which indicates a time related to the disappearance of GP zones.