On the influence of crystallography and dendritic microstructure on micro shear behavior of single crystal Ni-based superalloys

Abstract

An in-situ SEM micromechanical test technique is used to investigate the response of a Ni-based single crystal superalloy to double shear loading. The present work shows that micro double shear testing can detect mechanical differences between interdendritic and dendritic regions with γ′-volume fractions of 77% and 72%, respectively, i.e., the interdendritic regions exhibit a larger flow stress than the dendritic regions. These micromechanical differences are apparent when micro double shear specimens are oriented for single-slip while they appear to be overshadowed by dislocation interactions, when multiple-slip is promoted. Sudden deformation events are observed to occur concomitantly with the formation of shear steps (localized plastic deformation) at the surface of the shear zones during single-slip. The micro double shear specimens oriented for single-slip show very low work-hardening. In contrast, much higher stresses are required to plastically deform micro double shear specimens oriented for multiple-slip which exhibit stronger work-hardening. No sudden deformation events could be detected for multiple-slip which results in a more homogeneous deformation of the shear zones (absence of localized plastic deformation).