Tensile properties of high-purity nickel stressed in alkali metal environments

Abstract

Tensile failure of high-purity (99.99%) nickel varied systematically with the chemistry of alkali metal environments. Failure was by microvoid coalescence when stressed to destruction in argon, caesium, rubidium and potassium at 250 ~ The ultimate tensile strengths ,were about 250 MPa and the elongations at failure were approximately 45%. The fracture surfaces of samples tested in sodium displayed evidence of intergranular and transgranular cleavage, but the strength and ductility values were similar to those of samples tested in argon. However, failure in lithium was predominantly by intergranular cleavage, and the average ultimate tensile strengths and elongations to failure were only 10-7 MPa and 6%. Intergranular cleavage and severe embrittlement was caused also by sodium containing more than 0.2% lithium, but pre-exposure and slow straining had little influence. It is concluded that embrittlement by lithium is a physical process that can be related to parameters such as interfacial energies.