Origin of strain localization at twin boundary in Inconel 718 superalloy fabricated by laser powder bed fusion

Abstract

Microscale strain evolution and mechanistic origin of strain localization of Inconel 718 superalloy fabricated by laser powder bed fusion was investigated. Strain maps obtained by in-situ high resolution digital image correlation (HRDIC) demonstrate that localized dislocation activities and severe strain localization occur along the coherent twin boundaries (TBs). Such localized dislocation plasticity along TBs exhibits no dependency on the elastic anisotropy and the length of TBs, and the determining factor of the occurrence of localization is the maximum Schmid factor of the TBs. By employing correlative characterizations of TBs, γ″ precipitate and dislocation slip bands, it is found out that the precipitation of V-shaped γ″ along TBs incurs the formation of precipitates denuded zones, which takes the responsibility for localized plasticity and severe strain localization at TBs.