Dryburgh Paul, Smith Richard J, Marrow Paul, Lainé Steven J, Sharples Steve D, Clark Matt, Li Wenqi
Optics and Photonics Group, Faculty of Engineering, University Park, University of Nottingham, NG7 2RD, UK.
Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, CB3 0FS, UK.
Ultrasonics. 2020 Dec;108:106171. doi: 10.1016/j.ultras.2020.106171. Epub 2020 May 29.
Throughout our engineered environment, many materials exhibit a crystalline lattice structure. The orientation of such lattices is crucial in determining functional properties of these structures, including elasticity and magnetism. Hence, tools for determining orientation are highly sought after. Surface acoustic wave velocities in multiple directions can not only highlight the microstructure contrast, but also determine the crystallographic orientation by comparison to a pre-calculated velocity model. This approach has been widely used for the recovery of orientation in cubic materials, with accurate results. However, there is a demand to probe the microstructure in anisotropic crystals - such as hexagonal close packed titanium. Uniquely, hexagonal structure materials exhibit transverse isotropic linear elasticity. In this work, both experimental and simulation results are used to study the discrete effects of both experimental parameters and varying lattice anisotropy across the orientation space, on orientation determination accuracy. Results summarise the theoretical and practical limits of hexagonal orientation determination by linear SAW measurements. Experimental results from a polycrystalline titanium specimen, obtained by electron back scatter diffraction and spatially resolved acoustic spectroscopy show good agreement (errors of ϕ=5.14° and Φ=6.99°). Experimental errors are in accordance with those suggested by simulation, according to the experimental parameters. Further experimental results demonstrate dramatically improved orientation results (Φ error <1°). Demonstrating the possibility of achieving results near the theoretical limit by strict control of the experimental parameters.
在我们构建的整个环境中，许多材料呈现出晶格结构。这种晶格的取向对于确定这些结构的功能特性（包括弹性和磁性）至关重要。因此，用于确定取向的工具备受追捧。多个方向上的表面声波速度不仅可以突出微观结构的差异，还可以通过与预先计算的速度模型进行比较来确定晶体取向。这种方法已广泛用于立方材料的取向恢复，结果准确。然而，人们需要探测各向异性晶体（如六方密堆积钛）的微观结构。独特的是，六方结构材料表现出横向各向同性的线性弹性。在这项工作中，实验和模拟结果都被用于研究实验参数以及整个取向空间中变化的晶格各向异性对取向确定精度的离散影响。结果总结了通过线性表面声波测量确定六方取向的理论和实际限制。通过电子背散射衍射和空间分辨声学光谱法从多晶钛试样获得的实验结果显示出良好的一致性（φ误差为5.14°，Φ误差为6.99°）。根据实验参数，实验误差与模拟结果相符。进一步的实验结果表明取向结果有了显著改善（Φ误差<1°）。这表明通过严格控制实验参数有可能获得接近理论极限的结果。
