Cast Inconel 718 Fracture Micrograph

This image of an investment cast Inconel 718 sample fracture surface was taken at 1000x magnification on a scanning electron microscope (SEM). This specimen has clear shearing across individual grains, indicating that the mode of fracture for this sample was brittle and largely transgranular. This sample did not experience plastic deformation before failing as seen by the voids and imperfections. The most noticeable feature of this image is the dendrite formation along the center of the image. During the casting process, this feature is formed due to directional cooling gradients along the edges of the mold cavity leading to variable rate material precipitation. A shrinkage void was created as this dendrite was formed due to the expulsion of impurities and gases. This shrinkage void weakened the sample and subsequently led to the location of the fracture in the tensile sample, by causing the fracture to form along the empty gap in the material’s structure.