使用连续截面法结合三维电子背散射衍射(3D-EBSD)技术研究了316L不锈钢的三维显微组织,重点分析了晶粒和晶界的三维形貌特征及各特征参数的分布规律,包括晶粒尺寸、晶粒表面积、晶粒的晶界面数、晶界尺寸和晶粒的平均晶界尺寸,并统计分析了各特征参数之间的关系。结果表明：316L不锈钢的三维晶粒和三维晶界的形貌特征参数均服从对数正态分布,各参数与晶粒尺寸之间的关系符合幂函数。另外,由于存在大量孪晶,造成316L不锈钢的三维晶粒形貌十分复杂,且尺寸越大的晶粒形貌越复杂,晶界面数越多,表面积越大,与等轴晶的偏离也越大。

Three-dimensional characterization of grains and grain boundaries is significant to study the microstructure of polycrystalline materials, and is the key to advance the subject of three-dimensional materials science (3DMS). In this work, the technique of serial sectioning by mechanical polishing coupled with 3D electron backscatter diffraction (3D-EBSD) mapping was used to measure the microstructure of a 316L stainless steel in 3D. Volume of the collected 3D-EBSD microstructure is 600 μm×600 μm×257.5 μm, which is quite large to study the 3D microstructure of structural materials with conventional grain size (20~60 μm). Dream3D and in-house developed Matlab programs were used to process the 3D-EBSD data, and subsequently ParaView was used to visualize the grains and grain boundaries in 3D. Combined usage of these tools and in-house programs make the possibility that not only 3D grains but also 3D grain boundaries can be studied in both morphology and quantification. In total, 1840 grains and 9177 grain boundaries are included in the measured 3D-EBSD microstructure. The 3D morphological characteristics and size distributions of grains and grain boundaries in the 316L stainless steel were investigated, including 3D grain size, grain surface area, boundary quantity per grain, grain boundary size and the average boundary size per grain, as well as relationships between these morphological parameters were discussed. Results showed that distributions of all of these morphological parameters of 3D grains and grain boundaries in the polycrystalline 316L steel can be well represented by log-normal distribution, and all relationships of these parameters versus grain size can be well represented by power function. Additionally, the 3D morphologies of most grains in the 316L stainless steel deviate from the ideal equiaxed grains, having complex shapes due to existing of twins, such as semi-sphere shaped, plate shaped and some very complex grains. In many ways, the larger grains have more complex morphology with greater number of faces, larger surface area and larger deviation from equiaxed grains.