Effect of the grain size on the microtensile deformation and fracture behaviors of a nickel-based superalloy via EBSD and in-situ synchrotron radiation X-ray tomography

Two-dimensional (2D) and three-dimensional (3D) characterizations of microtensile deformation of a nickel based superalloy were realized by scanning electron microscope (SEM), transmission electron microscope (TEM), electron backscatter diffraction (EBSD), and in-situ synchrotron radiation X-ray tomography (SRXT). The mechanical properties, strain evolution, defect development and fracture behavior were studied. Analysis of the orientation distribution function indicated that the applied tensile deformation plays a key role in the shear deformation texture components, with a mixture of {0 1 1}<2-1 1>and {1 1 2}<1 1 1>components being observed. The yield strength, tensile strength, and fracture elongation decrease with the grain size. A 2D visualization study using EBSD showed that the increase of grain size induces inhomogeneous plastic deformation. A 3D visualization study using in-situ SRXT showed that voids preferentially formed at grain boundaries. The free surface roughening increases with the grain size. The occurrence of the free surface roughening leads to the strain localization and a decreased fracture strain when there are only a few grains across the specimen thickness during microtensile deformation. Defect development and fracture morphology analysis showed that the intergranular fracture and the transgranular fracture jointly control the fracture behavior of the superalloy.