Geometrical influence for creep damage evaluation of IN738LC using electron backscatter diffraction

Abstract

The Ni-based superalloy IN738LC is an outstanding heat-resistant material, but it does have the disadvantage of being brittle. Therefore creep degradation such as deformation of components or initiation of microscopic creep voids only appear at the end of its available creep life. To date, electron backscatter diffraction (EBSD) in conjunction with scanning electron microscopy has been used for damage evaluation. Some results showed that the misorientation was correlated with the magnitude of macroscopic plastic or creep strains. In this study, by using the EBSD method, the characteristics of the change and distribution tendencies of crystallographic misorientation on creep life have been investigated. In addition, the geometrical influence of stress concentrated areas for misorientation analysis has been investigated, which is important to evaluate damage in practical components like blades. As a result, the grain reference orientation deviation parameter which corresponds to the spread of creep strain has been found to be useful to estimate creep life among the misorientation parameters. Also, misorientation analysis allows the evaluation of creep damage before the appearance of obvious defects without being subjected to the geometrical influence of the stress concentrated areas.