Grain size effect on stress hysteresis of nanocrystalline NiTi alloys
Grain size effect on stress hysteresis of nanocrystalline NiTi alloys
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晶粒尺寸对纳米晶 NiTi 合金应力滞后的影响
DOI：
10.1016/j.jallcom.2016.07.168
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发表时间：
2016-12-15
影响因子：
6.2
通讯作者：
Cui, L. S.
中科院分区：
文献类型：
--
作者：
Shi, X. B.;Guo, F. M.;Cui, L. S.
本文通过对两种冷拔变形量分别为39%和75%的样品进行超弹性循环试验，研究了晶粒度对纳米晶NiTi合金超弹循环应力滞后的影响。透射电子显微镜和差示扫描量热仪分析表明，面积缩小率为75%的样品在加热时经历了一个晶化过程，退火后含有少量的位错。分析了NiTi合金晶界迁移的激活能，得到晶界迁移激活能为353.6+/-15.3kJ/m ol。滞后分析表明，退火后样品的应力滞后随晶粒度的减小而增大。我们认为在纳米晶NiTi合金中，晶界的单位体积能量耗散大于晶核的单位体积能量耗散，这是造成这种晶粒度效应的原因。然而，面积缩小率为39%的样品在加热时没有经历晶化过程，并且在退火后的样品中出现了许多位错。退火后变形量为39%的样品的应力滞后随位错密度的增加而减小。结果表明，晶粒度效应和位错密度效应对纳米晶NiTi合金应力滞后的影响是不同的。(C)2016爱思唯尔B.V.保留所有权利。
In this paper, the grain size effect on the stress hysteresis of a nanocrystalline NiTi alloy during superelastic cycling was investigated by testing two types of samples with 39% and 75% cold-drawn area reduction. The TEM microstructure and DSC analysis reveal that the sample with 75% area reduction experiences a crystallization process upon heating and contains few dislocations after annealing. The activation energy for grain boundary migration of the NiTi alloy was analysed and found to be 353.6 +/- 15.3 kJ/mol. The hysteresis analysis shows that the stress hysteresis of the samples after annealing increases with decreasing grain size. We propose that the energy dissipation per volume of grain boundary is larger than that of the grain core in the nanocrystalline NiTi alloy, which contributes to this grain size effect. However, the sample with 39% area reduction does not experience the crystallization process upon heating, and many dislocations are encountered in the samples after annealing. The stress hysteresis of the samples with 39% area reduction after annealing decreases with increasing dislocation density. The results clarify the difference between the grain size effect and the dislocation density effect on the stress hysteresis of nanocrystalline NiTi alloys. (C) 2016 Elsevier B.V. All rights reserved.