Microprobe-type measurement of Young's modulus and Poisson coefficient by means of depth sensing indentation and acoustic microscopy

Abstract

Nano-indentation and hyper frequency scanning acoustic microscopy (SAM) are mechanical microprobe techniques allowing measurement of the near-surface elastic response. In the first case, the composite modulus E/(1−ν 2) can be assessed using the slope of the elastic unloading plot. The second technique allows measurement of Rayleigh wave velocity, which depends on Young's modulus, Poisson ratio and density, to be measured through material acoustic signature. In both cases only one of the elastic constants may be determined using a hypothesis on the other one (usually on the Poisson coefficient). In the present paper we show that by joining both techniques for the same specimens, E and ν can be deconvoluted. Effectiveness of this deconvolution method is first tested on two well-known materials. Results on fused silica ( E=72.9 GPa; ν=0.17) as well as bulk aluminium ( E=69.6 GPa; ν=0.33) are in very good agreement with values commonly found in the literature. The method is finally applied on AlCuFe alloys presenting similar compositions but with different phases (icosahedral, tetragonal and cubic). This study shows the importance of crystallographic structure on elastic behaviour, especially on the Poisson ratio which ranges from ν=0.39 for the icosahedral phase down to ν=0.12 for the tetragonal phase.