孿晶界在316L不銹鋼三維晶界網絡中的分布特征

孿晶界在316L不銹鋼三維晶界網絡中的分布特征Distribution characteristics of Twin-boundaries in Three-dimensional Grain Boundary Network of 316L Stainless Steel

使用三維電子背散射衍射技術（3D-EBSD）對316L不銹鋼的3D晶界網絡進行表征分析，研究了孿晶界在三叉界角和四叉界角中的分布規律，以及孿晶界沿晶粒和沿晶界的分布規律，揭示孿晶界在316L不銹鋼3D晶界網絡中的分布特征。分析結果表明，316L不銹鋼3D晶界網絡中的孿晶界數量比低于面積比；大部分三叉界角中有1個或者沒有孿晶界，含有2個孿晶界的三叉界角很少；大部分四叉界角中有1~2個孿晶界，含有3個孿晶界的四叉界角很少；每個3D晶粒平均有11個晶界面，其中孿晶界面數平均為2.03；平均每個晶界與9.35個晶界線接觸，其中孿晶界個數平均為1.99。另外，從整個晶界網絡層面上討論了3D隨機晶界網絡的連通性問題。

Grain boundaries are sources of failure and weakness due to their relatively excess free volume compared to the lattice of polycrystalline materials exposed to aggressive environment. The control of grain boundary degradation has become one of the key issues of Materials Science and Engineering. It has been found that the coincidence site lattice (CSL) boundaries, especially ∑3 (the twin boundaries), have stronger resistance to intergranular degradation than random boundaries. Materials with a high proportion of CSL boundaries that could disrupt the connectivity of random boundaries have better performance to resist intergranular failures. However, the distribution characteristics of twin boundaries in grain boundary network are still unclear. In this work, three-dimensional electron backscatter diffraction (3D-EBSD) was used to map the 3D grain boundary network of a 316L stainless steel. The topological characteristics of triple junction and quadruple junction in the presence of twin boundaries were investigated. The distribution of twin boundaries around grains and grain boundaries was analyzed. The results show that the twin boundary number fraction in the 3D grain boundary network is lower than the measured twin boundary area fraction, indicating that the average area per twin boundary is larger than random boundary. Most of triple junctions in the 316L stainless steel have one twin boundary. The proportion of triple junctions with two twin boundaries is about 9.4%. A quadruple junction has three twin boundaries at most. Most of quadruple junctions have one or two twin boundaries. About 7.9% of quadruple junctions have three twin boundaries. The 3D-EBSD data of 316L includes 1840 grains, 7353 random boundaries and 1824 twin boundaries. On average, a 3D grain in the 3D microstructure has 11 faces (39.85 neighboring faces that includes all boundaries of the grain and all boundaries that connected with the grain by lines or points), in which the number of twin boundaries is 2.03 (8.02) on average. A 3D grain boundary has 9.35 neighboring boundaries, in which the number of twin boundaries is 1.99 on average.

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