The three‐dimensional (3D) microstructures within the vicinity of the fine granular area (FGA) were investigated with synchrotron radiation nano‐computed tomography (CT). In this investigation, the very high cycle fatigue test of a high‐strength steel was carried out with an ultrasonic fatigue testing machine. Then, focused ion beam cutting was used to cut a part near the surface of the FGA. Finally, the 3D structure of the sample was obtained with the nano‐CT imaging. The results indicated that the base material was composed of various subgrains that are tens to hundreds nanometres in size. Through analysis of the slices, small granular areas consist of several subgrains. The statistical analysis of the subgrain size indicated that the subgrain size near the surface of the FGA is similar to that far from the surface of the FGA and near the fracture surface except the FGA. It indicated that the refinement has not been found by nano‐CT.

中文翻译：

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同步辐射纳米CT在细颗粒区域附近的结构表征

用同步辐射纳米计算机断层扫描（CT）研究了细颗粒区域（FGA）附近的三维（3D）微观结构。在这项研究中，使用超声波疲劳试验机对高强度钢进行了极高的循环疲劳试验。然后，使用聚焦离子束切割来切割FGA表面附近的部分。最后，通过nano-CT成像获得了样品的3D结构。结果表明，基材由大小为数十至数百纳米的各种亚晶粒组成。通过切片的分析，小的颗粒区域由几个子颗粒组成。对亚晶粒尺寸的统计分析表明，靠近FGA表面的亚晶粒尺寸类似于远离FGA表面且靠近断裂表面的亚晶粒尺寸，除了FGA。这表明，nano-CT尚未发现这种改进。