The Mechanism of Stress Corrosion Fracture of a Copper-Beryllium Alloy

Abstract

Abstract The process of stress corrosion fracture was investigated in a copper-beryllium alloy specimen exposed to different ammonia environments. Two basically different stages occur in this process. First, reactions leading to the formation of a crack, then formation and propagation of the crack. In the first stage, dissolution is probably the main effect of the corrosive environment resulting in a preferential attack on grain boundaries or on crystallographic planes. The distribution of solutes determines the areas of preferential attack (grain boundaries or crystallographic planes) and it depends on the aging conditions of the specimens. Plastic deformation and applied stress are not important factors in this stage. In the second stage, during the formation and propagation of the crack, the amount of plastic deformation, the value of applied stress and distribution of solutes are important. The main effect of the corrosive environment, in this stage, consists in the decrease of the surface free energy by a sorption process. Based on these observations a mechanism of stress-corrosion fracture in a copper-beryllium alloy specimen is proposed.