Effect of grain size on deformation and fracture of Inconel718: An in-situ SEM-EBSD-DIC investigation

The effects of grain size on tensile behavior of Inconel718 superalloy have been characterized by an in-situ tensile stage inside a scanning electron microscopy (SEM) combined with electron backscatter diffraction (EBSD) and digital image correlation (DIC) at room temperature. The microstructure evolution and mechanical properties of specimens under different heat treatments were performed and compared. The in-situ tensile test showed that the yield strength, ultimate tensile strength and reduction of cross section decrease with the increasing grain size. An in-situ EBSD study showed that with increasing stress the local plastic deformation become more inhomogeneous. An analysis combined in-situ SEM morphology evolution, DIC strain distribution and EBSD results indicated that the grains deformed coordinately. Geometrically necessary dislocation (GND) density depends on the grain size and the orientation of individual grains. The coordinated deformation ability decreased with increasing grain size. The fracture morphology showed that with the increase of grain size, the fracture mechanism transformed from the ductile transgranular fracture to the brittle intergranular-transgranular mixed fracture.