纳米Ni在77 K温度下压缩行为的研究

利用低温力学测试系统研究了电化学沉积纳米Ni在77 K温度下的压缩行为. 室温下纳米Ni 的屈服强度为 2.0 GPa, 77 K温度下的屈服强度为3.0 GPa, 压缩变形量则由室温的10%左右下降到5%. 借助应变速率敏感指数、激活体积、扫描电子显微和高分辨透射电子显微分析, 对纳米Ni的塑性变形机制进行了表征. 研究表明, 在77 K温度下的塑性变形主要是由晶界-位错协调变形主导, 晶界本征位错弓出后无阻碍地在晶粒内无位错区运动, 直至在相对晶界发生类似切割林位错行为. 同时分析了弓出位错的残留位错部分在协调塑性变形时起到的增加应变相容性和减小应力集中的作用. 利用晶界-位错协调机制和残留位错运动与温度及缺陷的相关性揭示了纳米Ni室温和77 K温度压缩性能差异的内在原因.关键词：塑性变形强度位错

Compression behavior of nanocrystalline nickel at 77 K

In this paper, compression test is carried on electrodeposited nano-crystalline (NC) Ni at 77 K. The results show that the NC Ni has extremely high compressive strengths: around 2.5 GPa at room temperature (RT), 3.5 GPa at 77 K, and moderate plasticity with 0.1 fracture strain at RT, 0.05 at 77 K. The strain rate sensitivity m and activation volume v are calculated, and scanning election microscope and high-resolution transmission election microscope are used to verify the deformation mechanism. Analysis indicates that the dislocation interaction with grain boundary (GB) dominates the deformation of NC Ni both at 77 K and RT. Based on the calculated values of m and v, the deformation process is described by considering the intrinsic dislocation of GB bowing out and expanding towards opposite GB in the inner grain dislocation-free zone. And the mechanism is studied in the residual dislocation parts affecting the increase of strain compatibility and the decrease of stress concentration. It is indicated that the difference in compression property between at RT and 77 K is relatated to grain boundary-dislocation coordination mechanism and relation between residual dislocation motion and temperature.
Keywords：plastic deformstrengthdislocation