Lin Yao, Liu Shan, Wu Tao, Wang Guangchun
Key Laboratory for Liquid-Solid Structural Evolution and Processing of Materials (Ministry of Education), Shandong University, Jinan 250061, China.
Materials (Basel). 2021 Dec 29;15(1):236. doi: 10.3390/ma15010236.
The "torsion and annealing" grain boundary modification of pure nickel wires with different diameters was carried out in this paper. The effects of torsional cycles as well as unidirectional/bidirectional torsion methods on grain boundary characteristic distribution and plasticity were investigated. The fraction of special boundaries, grain boundary characteristic distributions and grain orientations of samples with different torsion parameters were detected by electron backscatter diffraction. Hardness measurement was conducted to characterize the plasticity. Then, the relationship between micro grain boundary characteristics and macro plasticity was explored. It was found that the special boundaries, especially Σ3 boundaries, are increased after torsion and annealing and effectively broke the random boundary network. The bidirectional torsion with small torsional circulation unit was the most conducive way to improve the fraction of special boundaries. The experiments also showed that there was a good linear correlation between the fraction of special boundaries and hardness. The plasticization mechanism was that plenty of grains with Σ3 boundaries, [001] orientations and small Taylor factor were generated in the thermomechanical processes. Meanwhile, the special boundaries broke the random boundary network. Therefore, the material was able to achieve greater plastic deformation. Moreover, the mechanism of torsion and annealing on the plasticity of pure nickel was illustrated, which provides theoretical guidance for the pre-plasticization of nickel workpieces.
本文对不同直径的纯镍丝进行了“扭转与退火”晶界改性。研究了扭转循环次数以及单向/双向扭转方法对晶界特征分布和塑性的影响。采用电子背散射衍射检测不同扭转参数样品的特殊晶界比例、晶界特征分布和晶粒取向。通过硬度测量来表征塑性。然后，探索了微观晶界特征与宏观塑性之间的关系。研究发现，扭转和退火后特殊晶界，尤其是Σ3晶界增加，有效地打破了随机晶界网络。采用小扭转循环单元的双向扭转是提高特殊晶界比例的最有效方式。实验还表明，特殊晶界比例与硬度之间存在良好的线性相关性。其塑化机制是在热机械过程中产生了大量具有Σ3晶界、[001]取向且泰勒因子较小的晶粒。同时，特殊晶界打破了随机晶界网络。因此，材料能够实现更大的塑性变形。此外，阐述了扭转和退火对纯镍塑性的作用机制，为镍工件的预塑化提供了理论指导。
