孪晶界在316L不锈钢三维晶界网络中的分布特征

Distribution Characteristics of Twin-Boundaries in Three-Dimensional Grain Boundary Network of 316L Stainless Steel

使用三维电子背散射衍射(3D-EBSD)技术对316L不锈钢的3D晶界网络进行表征分析,研究了孪晶界在三叉界角和四叉界角中的分布规律,以及孪晶界沿晶粒和沿晶界的分布规律,揭示孪晶界在316L不锈钢3D晶界网络中的分布特征。分析结果表明,316L不锈钢3D晶界网络中的孪晶界数量比低于面积比;大部分三叉界角中有1个或者没有孪晶界,含有2个孪晶界的三叉界角很少;大部分四叉界角中有1～2个孪晶界,含有3个孪晶界的四叉界角很少;每个3D晶粒平均有11个晶界面,其中孪晶界面数平均为2.03;平均每个晶界与9.35个晶界线接触,其中孪晶界个数平均为1.99。另外,从整个晶界网络层面上讨论了3D随机晶界网络的连通性问题。

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 Σ3 （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.