High-cycle fatigue behavior of Haynes 282 superalloy subjected to accelerated ageing

The room temperature high-cycle fatigue behavior of Haynes 282 subjected to accelerated ageing at 750, 800 and 850 degrees C for different durations was studied. Ageing promotes the growth of gamma' precipitate and the formation of M6C and M23C6 carbides, topologically closed packed mu phase, but has limited influence on the grain growth. Although, fatigue strength increases with increasing ageing duration, at both 750 degrees C and 800 degrees C, contrasting variations in the same were observed with increasing ageing temperature. By measuring the fatigue striation spacings on fractured surfaces and using the results of a finite element model developed for unnotched bend specimens available in the literature, the Paris slopes, m, of aged and unaged samples were determined to be in the range of 3-4. The fatigue crack initiation stage, which is > 99 % of the total fatigue life, increases with increasing size of gamma', except for alloys aged at 800 degrees C and 850 degrees C. Deviations in the trend are attributed to the evolution of M6C carbides at temperatures > 800 degrees C at the MC/gamma interface. Implications of these results are discussed in the context of predicting the fatigue strength of Haynes 282 utilized in service for long durations.