选用直流电沉积制备平均晶粒尺寸为27.2 nm,宽晶粒尺寸分布(5～120 nm)的纳米镍(简称宽晶纳米镍),在室温采用拉伸应变速率(ζ)突变法测量其应变速率敏感指数(m).发现m随的减小而增加,特别在小于2×10-5s-1时,m快速增加,m在=5×10-6s-1时达到0.054,表明塑性变形过程中晶界扩散、晶界滑移很可能被激活.在室温进行循环加载-卸载拉伸测试,结果表明宽晶纳米镍晶内存储位错的能力十分有限,当拉伸应力达到1052 MPa,应变为7.8%时,晶内位错密度达到饱和.通过对拉伸断口附近的TEM观察,证实宽晶纳米镍在塑性变形过程中存在显著的类似粗晶中的晶内位错滑移.
The electrodeposited nanocrystalline (nc) Ni with an average grain size of 27.2 nm and with a broad grain size distribution (BGSD) ranging from 5 to 120 nm was prepared. The tensile strain rate ((ε)) jump test was performed at room temperature to measure the strain rate sensitivity (m). The result shows that m increases with decreasing of . In particular, when is less than 2×10-5 s-1, m increases rapidly which reaches 0.054 at =5×10-6 s-1, indicating that the deformation mechanisms involved in grain boundary diffusion and sliding are possibly activated. The room temperature loading-unloading tensile test was carried out. The results show that the capability of storing dislocations in BGSD nc Ni is very limited and the dislocation density is saturated when the stress reaches 1052 Mpa with a strain of 7.8%. From the observation of TEM microstructures in the vicinity of tensile fracture, it is confirmed that there is significant intragranular dislocation sliding similar to that in coarse-grained materials in the process of plastic deformation of BGSD nc Ni.
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