Precipitate mediated plasticity at twin boundary in Nickel-based superalloy

Abstract

Twin boundaries (TBs) were reported to be the vulnerable site for strain localization in Nickel-based superalloys, but the mechanistic origin of localized plasticity is obscure and the effect from precipitates is still controversial. To clarify the role of γ″ in the localized plasticity, in-situ high-resolution digital image correlation (HRDIC) coupled with correlative multiscale characterizations were employed to reveal the microstructural strain evolution of Inconel 718 superalloy with different γ″ sizes. Pronounced localized plasticity and strain localization were observed at TBs in all samples regardless of the γ″ size, and the governing factor for the localized plasticity is the maximum Schmid factor associated with TBs. It is found that the formation of symmetric V-shaped γ″ along TBs results in easy channels for dislocation slip by destructing the precipitation strengthening adjacent to TBs, which takes the responsibility for the severe localized plasticity at TBs regardless of the γ″ size, and the size of γ″ only determines the distance between the localized slip bands and TBs.