Facile measurement of single-crystal elastic constants from polycrystalline samples

Abstract

Elastic constants are among the most fundamental properties of materials. Simulations of microstructural evolution and constitutive/micro-mechanistic modeling of materials properties require elastic constants that are predominately measured from single crystals that are labor intensive to grow. A facile technique is developed to measure elastic constants from polycrystalline samples. The technique is based upon measurements of the surface acoustic wave velocities with the help of a polydimethylsiloxane film grating that is placed on a polished surface of a polycrystalline sample to confine surface acoustic waves that are induced by a femtosecond laser and measured using pump-probe time-domain thermoreflectance. Electron backscatter diffraction is employed to measure the crystallographic orientation along which the surface acoustic wave propagates in each grain (perpendicular to the polydimethylsiloxane grating). Such measurements are performed on several grains. A robust mathematical solution was developed to compute the surface acoustic wave velocity along any crystallographic orientation of any crystal structure with given elastic constants and density. By inputting various starting values of elastic constants to compute the surface acoustic wave velocities to match experimental measurements in several distinct crystallographic orientations using an optimization algorithm, accurate elastic constant values have been obtained from seven polycrystalline metal samples to be within 6.8% of single-crystal measurements. This new technique can help change the current scenario that experimentally measured elastic constants are available for only about 1% of the estimated 160,000 distinct solid compounds, not to mention the significant need for elastic constants of various solid solution compositions that are the base of structural materials.

Mechanical Properties in Metal–Organic Frameworks: Emerging Opportunities and Challenges for Device Functionality and Technological Applications

“…Brillouin spectroscopy measurements require large MOF single crystals that preclude the study of polycrystalline morphologies. Recently, a novel technique was presented, in which surface acoustic wave velocities induced by a femtosecond laser are measured using polished surfaces of polycrystalline samples under a polydimethylsiloxane film grating . This approach was demonstrated through the accurate measurement of the elastic constants in seven polycrystalline metal samples and yielded agreement within 6.8% of the single crystal measurement values.…”

Thermal diffusivity determination using heterodyne phase insensitive transient grating spectroscopy

“…TGS measurements are carried out along primary surface directions 100 {001}, 111 {011}, and 112 {111} by fixing the rotation of the sample with respect to the optical arrangement. These directions are indicated by the manufacturer and confirmed by comparing the measured surface acoustic wave velocity to values computed for these surface directions using elastic theory [20,21]. In materials with phonon-dominated thermal transport, several authors have shown that thermal diffusivities measured using short-wavelength excitations, like those used in TGS, will be smaller than bulk diffusivities [4,11].…”

Resonant ultrasound spectroscopy: Sensitivity analysis for anisotropic materials with hexagonal symmetry

“…Unlike RUS, SAW is a directional phenomenon; phase speed depends on both the crystallographic plane on which the measurements are taking place and the direction of wave propagation on that plane. Moreover, SAW measurements can be conducted on extremely small surfaces, such as on single grains in polycrystalline samples [28].…”