Grazing incidence ultrasonic microscopy (GIUM) is an experimental method for visualising the microstructures of polycrystals with local preferential orientations. It has previously been demonstrated on an austenitic stainless steel weld, exposing grains much smaller than the propagating wavelength, but the physical mechanism of the method has only been proposed as a hypothesis. In this paper, we use grain-scale finite element simulations based on the EBSD measurements to verify the principles behind GIUM images further and to assess how deep does the method penetrate the component under examination. The simulations indicate that while lateral contraction of grains contains microstructure signatures, the free surface effect is the crucial factor contributing to the generation of the images. Further, we show that only features up to the depth in the order of the average grain size in that direction can be visualised.

掠入射超声显微镜（GIUM）是一种用于可视化具有局部优先取向的多晶微观结构的实验方法。先前已经在奥氏体不锈钢焊缝上进行了证明，该晶粒暴露出的晶粒远小于传播波长，但该方法的物理机理仅作为假设提出。在本文中，我们使用基于EBSD测量值的晶粒度有限元模拟来进一步验证GIUM图像背后的原理，并评估该方法能深入到所检查的组件中。模拟表明，尽管晶粒的横向收缩包含微观结构特征，但自由表面效应是促成图像生成的关键因素。进一步，