S. I. Rokhlin, L. Yang, E. Kahana, L. Wang, X. Bin, The Ohio State University, Columbus, OH; P. B. Nagy, University of Cincinniti, Cincinnati, OH; M. P. Blodgett, US Air Force Research Laboratory, Wright-Patterson AFB, OH
Nondestructive evaluation of residual stresses and of residual stress relief in service conditions has great significance for reliability of turbine engine components. It is important to achieve better fundamental understanding of relations between nondestructive signature and material properties such as hardness, plasticity, cold-work and residual stress. In this work a nanoindentation technique is explored to determine the micromechanical properties and their relation to different levels of cold work in Ni based superalloys. It is shown that cold work has strong effect on hardness and yield stress. Significant size effect has been observed in indentation responses. Nanoindentation measurements were performed on the shot peened Ni based superalloy sample. For this, the sample was cross-sectioned and hardness was measured as function of depth from the sample surface. Reasonable correlation has been observed between dependences on depth of hardness and of cold work and residual stresses measured by X-ray diffraction. Also the cold work induced by spherical indentation, which produce roughness comparable to that from shot peening, has been investigated. The nanoindentation results are compared with non contact measurements of electrical conductivity.
Summary: Nondestructive evaluation of residual stresses and of residual stress relief in service conditions has great significance for reliability of turbine engine components. It is important to achieve better fundamental understanding of relations between nondestructive signature and material properties such as hardness, plasticity, cold-work and residual stress. In this work a nanoindentation technique is explored to determine the micromechanical properties and their relation to different levels of cold work in Ni based superalloys. It is shown that cold work has strong effect on hardness and yield stress. Significant size effect has been observed in indentation responses. Nanoindentation measurements were performed on the shot peened Ni based superalloy sample. For this, the sample was cross-sectioned and hardness was measured as function of depth from the sample surface. Reasonable correlation has been observed between dependences on depth of hardness and of cold work and residual stresses measured by X-ray diffraction. Also the cold work induced by spherical indentation, which produce roughness comparable to that from shot peening, has been investigated. The nanoindentation results are compared with non contact measurements of electrical conductivity.
