Dimensionless contact stiffness model to unveil the strain rate effect of nickel-based single crystal superalloy by nanoindentation

The strain rate effect of nickel-based single crystal superalloy DD6 is studied by nanoindentation experiments. Nanoindentation tests are conducted under load control to investigate the indentation response of nickel-based single crystal superalloy DD6 at loading rates varied from 10 to 1000 mN/min. It is found that when the loading rate is 110mN/min, the contact stiffness mechanism changes as the loading rate changes from low to high. The indentation residual morphology also shows that, when the loading rate is higher than 110mN/min, the residual indentation morphology begins to show obvious slip trace, which is consistent with the transition mechanism of contact stiffness. The relationship between the contact stiffness and the strain rate measured by nanoindentation is revealed, the theoretical framework between them is established and the dimensional analysis is conducted. The dimensionless contact stiffness model proposed can effectively calculate the indentation response of nickel-based single crystal superalloy DD6 in the loading rate range of 10-1000mN/min. Once the loading rate is determined, the model can extract the contact stiffness of the material.