Deformation behaviour and microstructure of nanocrystalline electrodeposited and high pressure torsioned nickel
Deformation behaviour and microstructure of nanocrystalline electrodeposited and high pressure torsioned nickel
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DOI：
10.1016/j.actamat.2005.01.041
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发表时间：
2005-05-01
期刊：
影响因子：
9.4
通讯作者：
Victoria, M
中科院分区：
文献类型：
--
作者：
Dalla Torre, F;Sp채tig, P;Victoria, M
对两种类型的纳米晶（NC）Ni样品进行了显微组织分析和力学测试，并与粗晶（CG）Ni进行了比较。NC电沉积（艾德）Ni的特征在于21 nm的平均晶粒尺寸，窄的晶粒尺寸分布和在未变形条件下观察到的位错的情况下。NC高压扭转（HPT）Ni显示出105 nm的平均晶粒尺寸，具有宽的晶粒尺寸分布。在透射电子显微镜下观察到的晶粒显示出位错和位错胞。从拉伸和压痕试验中推导出的力学性能表明，NC艾德Ni的强度明显高于NC HPT Ni。这两种材料都显示出小于5%的有限总塑性变形和随着应力增加的加工硬化率的准线性下降。应变率跳跃试验表明，这两种材料的应变率敏感性相似，这是一个数量级高于CG镍。与CG Ni相比，NC Ni的表观活化体积V，p显著较小。NC艾德Ni显示Vap随应力增加而降低，而NC HPT Ni测量到V-ap增加。使用重复应力松弛技术，一个有效的激活体积和相关的参数描述的移动的位错密度的变化已被估计为NC艾德镍和CG镍，并讨论在可能的变形动力学。结果表明，NC艾德Ni的松弛实验表观活化体积是跳跃实验表观活化体积的3倍以上，而CG Ni的松弛实验和跳跃实验表观活化体积基本一致。这可以被认为是在将这种分析应用于20 nm晶粒尺寸的金属时失败的指示。(c)2005 Acta Materialia Inc.由爱思唯尔有限公司出版。保留所有权利。
Microstructural analysis and mechanical testing have been performed on two types of nanocrystalline (NC) Ni samples and compared to coarse-grained (CG) Ni. The NC electrodeposited (ED) Ni is characterized by a mean grain size of 21 nm, a narrow grain size distribution and the absence of dislocations observed in undeformed conditions. NC high pressure torsioned (HPT) Ni shows a mean grain size of 105 nm with a broad grain size distribution. Grains observed in transmission electron microscopy exhibit dislocations and dislocation cells. The mechanical properties deduced from tensile and indentation tests of NC ED Ni show a significantly higher strength than the one of NC HPT Ni. Both materials show a limited total plastic deformation of less than 5% and a quasi-linear decrease in the work hardening rate with increasing stress. Strain rate jump tests have shown for both materials similar strain rate sensitivities, which are one order of magnitude higher than in CG Ni. A significantly smaller apparent activation volume V,p has been measured for NC Ni as compared to CG Ni. NC ED Ni shows a decrease in Vap with increasing stress, while an increase of V-ap was measured for NC HPT Ni. Using the repeated stress relaxation technique, an effective activation volume and associated parameters describing the change in the mobile dislocation density have been estimated for NC ED Ni and CG Ni and are discussed in terms of the possible deformation kinetics. Results have shown that the apparent activation volume of NC ED Ni deduced from relaxation tests is more than three times higher than the one deduced from jump tests, while in CG Ni both methods give consistently similar values. This can be taken as an indication for a breakdown in the application of such analysis to 20 nm grain sized metals. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.