A further look at the nano/micro-indentation method for measuring and ranking Young’s modulus and hardness of materials

Abstract

Determination of the intrinsic Young's modulus (E) is essential for material design and applications. However, the commonly used micro/nano-indentation method does not give accurate intrinsic Young's modulus, since the measured modulus comes from the damaged zone under the indent tip. In this study, we analyze the intrinsic Young’s modulus or that without local damage caused by indentation, and determine that the intrinsic Young’s modulus can be determined by extrapolation of the E ~ load curve as the indentation load approaches zero. To support this finding, indentation behaviors of five ceramic materials (Al2O3, Si3N4, ZrO2, glass and cemented WC/Co) were analyzed and compared with those determined using an acoustic method. The intrinsic Young's modulus measured, e.g., using the acoustic method, are appropriate for material ranking, while Young's moduli of different materials measured by indentation under the same load could give misleading information because of different degrees of local damage to the materials under the indenter. Underlying mechanisms for the observed phenomena shown in this novel and unqiue study are elucidated based on the interatomic bonding. Hardness versus load curves show trends similar to those of Young’s modulus. However, unlike the Young’s modulus, the hardness values measured under the same load can be directly used to rank materials; the reason behind is also discussed.