Martensitic phase transformations and twinning in epitaxially grown Nickel Titanium films

外延生长镍钛薄膜中的马氏体相变和孪生

• 批准号: 383432286
• 负责人: Privatdozent Dr. Sebastian Fähler
• 金额: --
• 依托单位: Institut für Ionenstrahlphysik und Materialforschung
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2017
• 资助国家: 德国
• 起止时间: 2016-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/383432286?language=en
• 关键词: Martensitic; phase; transformations; twinning; epitaxially

In this research project we study epitaxially grown NiTi shape memory alloy films. These thin films (with thicknesses ranging from about 100 nm to several microns) are used as a model system for highly precise, fundamental investigations on martensitic transformations, for instance to analyze on several length scales the self-similar martensitic microstructures in NiTi. Most importantly, we will consider the key question whether the morphology of martensitic microstructures in NiTi is determined by thermodynamic equilibrium processes or by the most easily accessible transformation paths. The planned experimental work considers epitaxial growth of NiTi films on different MgO and Al2O3 substrates. Moreover, we use X-ray diffraction, atomic force microscopy and electron microscopy methods to analyze the twinned microstructures and the corresponding textures of NiTi martensites. In in-situ investigations, the martensitic phase transition is documented by atomic force microscopy measurements during cooling, with a particular focus on nucleation mechanisms. The stress-induced transformation is triggered using nanoindentation and small-scale tensile testing of free-standing thin films; the activated twinning systems are analyzed by means of micromechanical and continuum mechanical calculations considering elastic anisotropy of both high and low temperature phases. The experimental and theoretical results of our investigations on the well-defined model system will allow to describe formation of martensitic microstructures in NiTi across several relevant length-scales. The effect of different twin boundary energies on the formation of hierarchically structured martensites will be considered, and a comparison with the multi-step nucleation model, where the kinetics of the phase transition is determined by the pathway with the lowest energy barrier, will be performed.

在此研究项目中，我们研究了外延生长的NITI形状记忆合金膜。这些薄膜（厚度从约100 nm到几微米不等）用作模型系统，用于高度精确，基本研究Martensenitic变换，例如，分析了NITI中自相似的Martensenitic微观结构的几个长度。最重要的是，我们将考虑NITI中马氏体微观结构的形态是由热力学平衡过程或最容易访问的转换路径确定的。计划的实验工作认为NITI膜在不同的MGO和AL2O3底物上的外延生长。此外，我们使用X射线衍射，原子力显微镜和电子显微镜方法来分析二元的显微结构和NITI Martensites的相应纹理。在原位研究中，在冷却过程中，原子力显微镜测量值记录了马氏体相变，特别关注成核机制。使用纳米凹痕和自制薄膜的小尺度拉伸测试触发了应力诱导的转化。考虑到高温和低温相的弹性各向异性，通过微力机械和连续机械计算对激活的双胞胎系统进行了分析。我们对定义明确的模型系统的研究的实验和理论结果将允许描述在几个相关长度尺度上NITI中马氏体微观结构的形成。将考虑不同的双边界能对层次结构化的马氏体形成的影响，并与多步成核模型进行比较，其中相变的动力学由具有最低能量屏障的途径确定。