Orientation-induced fluctuations of elastic modulus by Berkovich nanoindentation

Nanoindentation is widely employed to evaluate elastic properties of crystalline materials; however, the influence of in-plane rotation of non-axisymmetric indenters on elastic modulus extraction in elastically anisotropic single crystals remains insufficiently quantified. In this study, the effect of Berkovich indenter rotation on elastic modulus measurements performed on the [001] surface of a DD6 Ni-based single-crystal superalloy is systematically investigated. By combining nanoindentation experiments with finite element simulations, it is demonstrated that indenter rotation alone—without any change in crystallographic orientation—induces reproducible, orientation-dependent fluctuations in the apparent elastic modulus. Two finite element frameworks are employed for comparison: a crystal elasticity-based finite element model (CE-FEM) and a macroscopic anisotropic elastic model (Macro-FEM). Their close agreement under purely elastic conditions confirms that the observed modulus fluctuations originate from an intrinsic geometry–crystal coupling between the asymmetric Berkovich indenter and elastic anisotropy, rather than from constitutive modeling artifacts. Experimental results further reveal that the orientation-dependent modulation of the measured modulus persists under realistic testing conditions, indicating that indenter orientation can constitute a non-negligible source of systematic variation in high-precision nanoindentation measurements. By systematically comparing Berkovich and spherical indentation responses and analyzing orientation-dependent trends, this work establishes indenter rotation as an intrinsic, geometry-driven factor affecting elastic modulus extraction in anisotropic single crystals. The findings provide practical guidance for improving the reliability and interpretability of nanoindentation-based elastic characterization in anisotropic materials.