Strain localization in the Alloy 718 Ni-based superalloy: From room temperature to 650 °C

Irreversible deformation in relation to the microstructure was investigated for a polycrystalline Ni-based superalloy (Alloy 718) from room temperature to 650 degrees C using high -resolution digital image correlation (HR-DIC) techniques. Interrupted tensile tests were performed under a protective atmosphere to ensure the stability of the speckle pattern to track kinematics fields from surface analyses. In -plane strain localization was captured using HR-DIC on scanning electron microscopy (SEM) images. A statistical analysis of different strain localization events in relation to the microstructural features was conducted, i.e., intragranular slip localization, slip localization parallel to and near ������3-twin boundaries (������3-TB), and grain boundary sliding (GBS). Alloy 718 exhibited slip localization at room temperature and 350 degrees C. Intense strain localization develops parallel and in the vicinity of ������3-TB from the onset of the microplasticity. Few intense slip stimulated -grain boundary sliding events were found due to slip localization on both grains adjacent to the grain boundary. At 650 degrees C, Alloy 718 experienced grain boundary sliding at the onset of the yield without particular slip localization in adjacent grains. At lower temperatures, strain localization parallel to and near 3-TB was intense, and intragranular slip localization intensified with increasing macroscopic deformation. Particular microstructural configurations were found at 650 degrees C leading to premature damage: (i) sub -surface cavitation at grain boundaries, and (ii) grain boundary cracking due to intense shearing near a 3-TB.