Design of High Temperature Shape Memory Alloys

最近，人们对高温形状记忆合金的性能非常感兴趣，这将扩大这些材料的利用。形状记忆合金的独特之处在于它们在变形后能恢复到原来的形状。本课题的研究重点是开发具有400摄氏度以上高温形状记忆合金。晶体学和原子位移导致双胞胎的产生，原子的重排，将通过中尺度模型进行研究。将对组合物进行优化，以控制材料中二次相的强度，从而控制决定材料行为的相变的可逆性。该研究还将深入研究这些材料的样品制备过程，包括多晶和单晶。该研究将包括测量加载和卸载以及在应力下加热和冷却的行为的实验，以开发具有三元添加剂的镍，钛，钴和铁基形状记忆材料的几种潜在成分的耐高温性。提出的局部位移和应变的测量将为这些材料的原子变形面和孪生开始时的预测应力提供关键的检查。这些测量将使用数字图像相关技术进行，该技术也将在本研究中得到改进。该研究的预期收益是建立可在更高温度下工作的多组分形状记忆合金，具有驱动能力，可使航空航天和其他高温行业受益。目标是开发具有形状记忆功能的高温合金，同时不影响强度、延展性和耐久性。该研究的科学益处包括更好地理解基于潜在成分、晶体学和微观结构的机械响应。该研究的教育效益将通过准备一本关于形状记忆的专著和一系列结合原子计算和介观理论的讲座而得到加强。这将是形状记忆合金教学方法的一个进步，提升了材料科学和连续介质力学的观点和理解。

There is a recent, significant interest in high temperature shape memory alloy capabilities that will broaden the utilization of these materials. Shape memory alloys are unique in their ability to return to their original shape after deformation. The research emphasis of this proposal is on the development of new high temperature shape memory alloys with capabilities above 400 degree Celsius. The crystallography and the atomic displacements leading to the creation of twins, a rearrangement of the atoms, will be investigated via meso-scale modeling. The compositions will be optimized to control the strengths of secondary phases within the material and hence the reversibility of the phase transformations which dictate the material behavior. The research will also hone in on the processing of these materials for sample preparation, including polycrystals and single crystals. The investigation will include experiments to measure the behavior during loading and unloading and heating and cooling under stress in order to develop high temperature resistance for several potential compositions of nickel, titanium, cobalt and iron based shape memory materials with ternary additions. The proposed measurements of local displacements and strains will provide a critical check on the atomic deformation planes and the predicted stress at the onset of twinning in these materials. These measurements will be made with digital image correlation techniques, which will also be advanced during this research. The expected benefit of the research is to establish multi-component shape memory alloys that can operate at higher temperatures with actuation capabilities that can benefit the aerospace and other high temperature industries. The aim is to develop high temperature alloys with shape memory functionality without compromising strength, ductility and durability. The scientific benefits of the research include a better understanding of the mechanical response based on the underlying composition, crystallography, and microstructure. The educational benefits of the research will be enhanced with the preparation of a monograph on shape memory and a series of lectures that combine atomistic calculations with mesoscopic theories. This will be an advancement in the pedagogical treatment of shape memory alloys elevating the materials science and continuum mechanics perspectives and understanding.