Abstract
Abstract Alloy 908 (UNS N09908), a Ni-based, low-thermal expansion superalloy, has been developed as a structural material for high-field, Nb3Sn, superconducting magnets. Alloy 908 is characterized by high strength and toughness at cryogenic temperatures while, at the same time, exhibiting a thermal expansion coefficient close to that of Nb3Sn. While ideally suited for service at cryogenic temperatures, Alloy 908 is susceptible to embrittlement if exposed to an oxygen-containing environment in the temperature range from 350°C to 750°C. In this study oxygen-induced embrittlement (OIE) in Alloy 908 has been investigated. Constant ΔK fatigue crack growth testing was used as a tool to explore the effect of oxygen on embrittling behavior. Crack growth rate, da/dN, was evaluated as a function of loading frequency, oxygen partial pressure, ΔK, and load ratio over the temperature range from 350°C to 750°C. The effect of oxygen manifested itself as a change in crack growth rate and crack path. Transgranular (TG) a...
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