Effect of crystallographic compatibility and grain size on the functional fatigue of sputtered TiNiCuCo thin films
Effect of crystallographic compatibility and grain size on the functional fatigue of sputtered TiNiCuCo thin films
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DOI：
10.1098/rsta.2015.0311
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发表时间：
2016-08
期刊：
影响因子：
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通讯作者：
C. Chluba;Wenwei Ge;T. Dankwort;C. Bechtold;R. L. Miranda;L. Kienle;M. Wuttig;E. Quandt
中科院分区：
文献类型：
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作者：
C. Chluba;Wenwei Ge;T. Dankwort;C. Bechtold;R. L. Miranda;L. Kienle;M. Wuttig;E. Quandt
晶体相容性对热转变稳定性的积极影响已经在文献中得到了广泛的研究。然而，它对实际应用中使用的形状记忆效应或超弹性稳定性的影响仍未得到解决。在本研究中，将一种高度相容的TiNiCuCo成分的溅射膜暴露在热循环和超弹性循环中，其变换矩阵的中间特征值为1±0.01。与以往的结果一致，该合金的热转变在40次循环中温度变化小于0.1 K，非常稳定；另一方面，发现超弹性降解行为强烈依赖于热处理参数。采用透射电子显微镜、原位应力极化显微镜和同步加速器分析了不同热处理试样的微观组织，揭示了不同热处理试样的相变差异。发现良好的晶体稳定性并不是避免缺陷产生的充分判据，而缺陷是保证高超弹性稳定性的保证。对于所研究的合金，小晶粒尺寸是提高组合物屈服强度和减少超弹性循环中功能退化的决定因素。本文是“低温材料相变温度的测量”主题的一部分。
The positive influence of crystallographic compatibility on the thermal transformation stability has been already investigated extensively in the literature. However, its influence on the stability of the shape memory effect or superelasticity used in actual applications is still unresolved. In this investigation sputtered films of a highly compatible TiNiCuCo composition with a transformation matrix middle eigenvalue of 1±0.01 are exposed to thermal as well as to superelastic cycling. In agreement with previous results the thermal transformation of this alloy is with a temperature shift of less than 0.1 K for 40 cycles very stable; on the other hand, superelastic degradation behaviour was found to depend strongly on heat treatment parameters. To reveal the transformation dissimilarities between the differently heat-treated samples, the microstructure has been analysed by transmission electron microscopy, in situ stress polarization microscopy and synchrotron analysis. It is found that good crystallographic stability is not a sufficient criterion to avoid defect generation which guarantees high superelastic stability. For the investigated alloy, a small grain size was identified as the determining factor which increases the yield strength of the composition and decreases the functional degradation during superelastic cycling. This article is part of the themed issue ‘Taking the temperature of phase transitions in cool materials’.