Evaluation of single crystal elastic stiffness coefficients of a nickel-based superalloy by electron backscatter diffraction and nanoindentation

J. Everaerts; C. Papadaki; W. Li; A. M. Korsunsky

Journal of the Mechanics and Physics of Solids 131 (2019) 303-312

A new methodology was developed in order to obtain single crystal elastic coefficients from nanoindentation experiments on a cubic polycrystal. The method consists of locating grains that are oriented with a 〈100〉, 〈110〉 or 〈111〉 direction near-parallel to the sample surface normal by means of electron backscattering diffraction. The reduced Young’s moduli of the selected grains are then determined by nanoindentation. Finally, the average reduced modulus and Euler angles of each grain are used as input for a least-squares optimisation to calculate the three independent stiffness coefficients, which can then be used to obtain Young’s modulus in any crystallographic direction. This technique, which was validated on a single crystal nickel-based superalloy (CMSX-4) with known elastic coefficients, was applied to a polycrystalline nickel-based superalloy (RR1000) with unknown elastic coefficients, resulting in a correct prediction of the general trend of increasing Young’s modulus from the 〈100〉 to the 〈110〉 to the 〈111〉 direction. The stiffness coefficients C11, C12 and C44 were found to be 282, 121 and 108 GPa, respectively. These results, which are representative of the γ/γ’ structure as a whole, are in good agreement with literature data on similar superalloys. By constructing a visual representation of the elastic anisotropy based on the crystallographic factor, it is shown that the observed anisotropy is lower compared to other alloys.

DOI: https://doi.org/10.1016/j.jmps.2019.07.011