Materials World Network: Deformation via the Transformation of Hierarchical Microstructures

该材料世界网络研究项目由Peter Müllner教授、William Knowlton教授和Res.Assisted共同完成。博伊西州立大学(BSU)的Paul Lindquist教授和德国波鸿鲁尔大学的Steffen Brinckmann和Alexander Hartmaier专注于具有层次化孪晶微结构的材料的变形机制。虽然这种微结构存在于形状记忆合金和铁弹性陶瓷等许多功能材料中，但本研究的实验部分主要集中在磁性形状记忆合金(MSMA)上。磁性形状记忆合金的力学性能和磁机械性能强烈依赖于孪晶组织的细节，而孪晶组织的细节可以通过适当的热-磁-机械训练处理来改变。对于具有单一孪生系统的训练有素的单晶，孪生应力很低(约0.1 Mpa)，磁场感应应变大(6-10%)，疲劳寿命短(约10,000次)。未经训练的马氏体层状孪晶单晶的孪生应力较高(约2 Mpa)，磁场感应应变小(约0.1%)，疲劳寿命长(超过1亿次)。层状孪晶组织的变形机制将在博伊西州立大学通过原位变形实验在所有长度尺度上进行实验研究，而数值研究将在鲁尔大学波鸿大学进行。实验包括在透射电子显微镜(微尺度)、扫描探针显微镜(介观尺度)和光学成像试验台(宏观尺度)中进行原位应变。孪晶组织的缺陷含量将通过实验研究得到。位错偶极子，即具有剪切位移场的介观线缺陷，代表了孪晶在所有层次上的位移场。将开发一个倾错动力学程序，并将其应用于大规模的数值研究。通过为数值研究提供实验数据，通过系统地改变实验和数值参数，将对具有复杂分层孪晶组织的(磁)形状记忆合金的力学(和磁力)性质有一个定量的基本理解。预计将对技术产生重大影响：通过这项研究获得的量化理解将使快速、高撤销、大行程和长寿命的MSMA执行器的开发成为可能，包括喷墨打印机的阀门和生物医学系统的微泵。该项目将产生将MSMA从研究实验室带入工业技术所需的计算工具。

This Materials World Network research project between Prof. Peter Müllner, Prof. William Knowlton, and Res. Assist. Prof. Paul Lindquist at Boise State University (BSU) and Profs. Steffen Brinckmann and Alexander Hartmaier at the Ruhr University Bochum, Germany, focuses on the deformation mechanism of materials with hierarchically twinned microstructures. While such microstructures occur in many functional materials including shape-memory alloys and ferroelastic ceramics, the experimental part of this study concentrates on magnetic shape-memory alloys (MSMAs). The mechanical and magneto-mechanical properties of magnetic shape-memory alloys strongly depend on details of the twin microstructure, which can be varied via appropriate thermo-magneto-mechanical training treatments. For well-trained single crystals with a single operating twinning system, the twinning stress is very low (about 0.1 MPa), the magnetic-field-induced strain is large (6-10 %), and the fatigue life is short (about 10,000 cycles). For un-trained single crystals with self-accommodated, hierarchically twinned martensite, the twinning stress is relatively high (about 2 MPa), the magnetic-field-induced strain is small (about 0.1 %), and the fatigue life is long (exceeding 100 million cycles). The deformation mechanism of hierarchically twinned microstructures will be studied experimentally at Boise State University on all length scales with in-situ deformation experiments while numerical studies will be performed at the Ruhr University Bochum. The experiments include in-situ straining in the transmission electron microscope (microscale), in the scanning probe microscope (mesoscale), and with optical imaging in the tensile test bench (macroscale). The defect content of the twin microstructure will be obtained from the experimental study. Disclination dipoles, i.e. mesoscopic line defects with a shear displacement field, represent the displacement fields of twins on all hierarchical levels. A disclination dynamics code will be developed and applied to a large scale numerical study. By supplying the numerical study with experimental data, and by systematically varying experimental and numerical parameters, a quantitative fundamental understanding of the mechanical (and magneto-mechanical) properties of (magnetic) shape-memory alloys with complex hierarchical twin-microstructures will be generated. A strong impact on technology is anticipated: The quantitative understanding gained with this study will allow the development of fast and high-rescission MSMA actuators with large stroke and long lifetime for applications including valves for ink-jet printers and micropumps for biomedical systems. This project will produce the computational tools required for leading MSMAs from the research laboratory to industrial technologies.