材料期刊网

应用电子背散射衍射技术 (EBSD) 和电子通道衍衬成像技术(ECC)研究了大应变量 (96%) 冷轧纯度为99.996\%的金属Ni在低温再结晶过程中Σ3晶界的
演化. 研究表明, 基于EBSD数据, Σ3晶界可以分为两类------孪晶型和非孪晶型Σ3晶界, 二者可通过晶界取向差与60°<111>的偏差Δθ来区分. EBSD定位观察再结晶过程的结果表明, 非共格孪晶是由共格孪晶发展而来; 绝大部分Σ3ⁿ (n>1)晶界由晶核与其n次孪晶相遇而形成, 并且晶界含量随着n的增加显著降低. 大部分非孪晶型Σ3晶界由孪晶型Σ3晶界与小角晶界(Σ1)相遇反应而来, 可能比孪晶型Σ3晶界更能够阻断大角晶界网络.

The concept of grain boundary engineering (GBE) has been proposed based on the fact that many studies have demonstrated that boundaries associated with low value coincident site lattice (CSL) misorientations show higher resistance to intergranular fracture and corrosion, reduced susceptibility to impurity segregation and superior ductility. It is commonly accepted that for fcc metals of low to medium stacking fault energy metals, including Ni and many Ni–alloys, the most important CSL boundary for the GBE process is a Σ3 boundary, the occurrence of which is dominated by the formation of annealing twins. Moreover, it has been found that repetitive thermo–mechanical processing can be used to increase further the fraction of Σ3 (and Σ3ⁿ (n >1)) boundaries. However, the mechanism for this is not yet clear. Therefore, an investigation on the evolution of Σ3 boundaries during recrystallization is important for understanding the mechanisms of GBE for those materials. In the present paper the evolution of Σ3 boundaries during recrystallization in a 96% cold–rolled sample of pure nickel f 99.996% purity has been explored using orientation maps obtained using electrn backscatter diffraction (EBSD). Each orientation map was taken from the same area after annealing for various times. Based on the EBSD data the Σ3 boundaries can be divided into two groups: "twin" type and "non–twin" type. These groups can be differentiated using a parameter of deviation angle (Δθ) of boundary misorientation to the ideal twin misorientation (60°<111>). During recrystallization incoherent twin boundaries are found to develop from coherent twin boundaries. It is found also that most Σ3ⁿ (n >1) boundaries are formed by impingement of a nucles with its n–order twins, and that the chance for such impingement events decreases significantly with increasing n. Most non–twin type Σ3 boundaries arise from impingement of Σ1 and twin type Σ3 boundares. Non–twin type Σ3 boundaries may be more effective than twin type Σ3 boundaries to develop a beneficial grain boundary network.