Effect of crystallographic properties on low cycle fatigue crack initiation at elevated temperature for Ni-based directionally solidified superalloy

Effect of crystallographic properties on low cycle fatigue crack initiation at elevated temperature for Ni-based directionally solidified superalloy

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Low cycle fatigue tests at elevated temperature were conducted on a Ni-based directionally solidified superalloy subjected to transverse loading.To investigate the effect of the arrangement and the orientation of crystal grains on the crack initiation, the electron back-scatter diffraction (EBSD) method was applied on the surface of the tested specimens.In addition, finite element analysis that considered the plastic behavior of crystal grains and the crystal grain shape Stem Mount Gasket on the specimen surfaces was performed to evaluate the relationship between the crack initiation and the local stress that develops near the grain boundaries.

The results are summarized below.As for the effect of crystallographic properties in the specimen surface, many cracks initiated near the grain boundaries that neighbored the grains whose secondary axis was inclined to the normal direction of specimen surface by more than 35 degrees because the longitudinal stress larger than the nominal stress developed near those boundaries.The crack location was not confirmed to correlate with the grain boundary misorientation between the neighboring grains on the surface.

However, most cracks initiated near the grain boundaries that neighbored the grain whose secondary axis was more inclined than the grain located in the opposite surface.The results of FEM analysis revealed that high stress developed near those grain boundaries.In addition, the location where high resolved shear stress developed generally corresponded to the crack location and that it correlated with the number of Right Arm crack initiation cycles.