Development of microscale bicrystal tensile testing for strength measurement of oxidized grain boundaries of alloy 600 exposed to PWR environments

Abstract

Abstract Nickel based alloys are widely used in power plants due to their superior corrosion and stress corrosion cracking resistance. Alloy 600 is the material of choice in steam generator tubes in pressurized water reactors (PWR). However, even in these materials oxidized grain boundaries are found which may lead to stress corrosion cracking in service. This work evaluates the cracking of oxidized grain boundaries on alloy 600. Novel micro tensile testing procedure was developed, delivering not just yield strength, ultimate tensile strength and elongation data, but also direct observation of the failure. The information obtained will help to understand the stress corrosion cracking susceptibility of this alloy. It was found that the orientations of the two grains adjacent to a grain boundary play an important role in determining its propensity to crack; it also determines whether blocked volume ratio is an important consideration. Furthermore, it is found that the grain boundary shear stress needs to be considered in addition to the grain boundary normal stress.