Dynamic embrittlement of nickel-based alloys

High-temperature brittle intergranular fracture is known to affect a wide range of engineering alloys in specific environments. Dynamic embrittlement is a time-dependent form of brittle intergranular fracture that occurs in many alloys when stress and elevated temperatures are applied in the presence of a surface-adsorbed embrittling element. The influence of grain-boundary character on the susceptibility to dynamic embrittlement has been recognized in prior studies, but a quantitative look at this influence has yet to be performed. Bicrystals with crystallographic orientations meant to mimic those of grain boundaries found in partially cracked IN718 polycrystalline material were tested in four-point bending. The results of these experiments along with a study of the composite effects of special grain boundaries in the polycrystal were used to show that well-ordered structures such as low-angle, Sigma3 and Sigma5 boundaries can be particularly resistant to the effects of dynamic embrittlement. Also, experiments with other nickel-based alloys showed dynamic embrittlement to be a generic phenomenon in high-strength engineering alloys exposed to aggressive environments.