Characterization of residual stress and its effect on mechanical properties of nickel–based single crystal superalloys by nanoindentation

Different indenters are used to measure the magnitude of residual compressive stress and characterize the influence of compressive residual stress on the mechanical response of nickel–based single crystal superalloy. Based on the reduced modulus obtained by a cylindrical flat punch indenter, the indentation hardness and actual projected contact area of the pyramidal indenter at loading segment are calculated, which avoid the effect of indentation sinking–in or piling–up. Furthermore, according to the Nix–Gao model and actual projected contact area, the indentation load–depth curves of the pyramidal indenter at loading segment can be reconstructed, which are not affected by the indentation size effect. Based on the corrected indentation load–depth curves, the magnitude of residual compressive stress is calculated according to the difference in the loading work of the pyramidal indenter, and verified by the calculation results of David's model. It is found that the elastic modulus and reduced modulus are not affected by the residual compressive stress; the indentation hardness, slope of the contact stiffness – depth curve and contact area show an increasing regime as residual compressive stress increases; residual compressive stress enhances the ability of NBSX to resist creep and plastic deformation.