Brittle behavior of a dilute copper-beryllium alloy at 200°C in air

Abstract

Intergranular cracking in a Cu-Be alloy tested in low-cycle fatigue at various partial pressures of oxygen was observed more than 20 years ago by Coffin. This phenomenon has also been observed in other copper alloys. Minute additions of zirconium were shown to improve the high temperature ductility of these alloys. This led to experiments to determine the effects of a zirconium addition to a cobalt-containing high strength, high conductivity Cu-Be alloy which showed intergranular cracking during hot-deformation processing. It is of interest to examine this phenomenon in the light of recent studies of dynamic embrittlement related to sulfur-induced intergranular cracking of low-alloy steels (stress-relief cracking) and to tin-induced intergranular cracking of Cu-Sn alloys. The dynamic embrittlement phenomenon involves the ingress of low-melting surface-adsorbed elements along grain boundaries under the influence of an applied tensile stress, in the manner of Coble creep. At any given temperature, the rate of ingress of low-melting surface-adsorbed elements along grain boundaries under the influence of an applied tensile stress, in the manner of Coble creep. At any given temperature, the rate of ingress, and thus the rate of cracking, varies with some power of the local stress. Because Cu-Be alloys can support very high stresses,more » one would anticipate that they could be susceptible to dynamic embrittlement in the presence of oxygen, a common embrittling element in metals. Accordingly, some preliminary experiments have been carried out on a dilute Cu-Be alloy with and without the presence of zirconium to see if its behavior is consistent with the dynamic embrittlement phenomenon.« less