Huang Xiangyang, Ackland Graeme J, Rabe Karin M
Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08854-8019, USA.
Nat Mater. 2003 May;2(5):307-11. doi: 10.1038/nmat884.
Shape-memory alloys (SMAs) are a unique class of metal alloys that after a large deformation can, on heating, recover their original shape. In the many practical applications of SMAs, the most commonly used material is NiTi (nitinol). A full atomic-level understanding of the shape-memory effect in NiTi is still lacking, a problem particularly relevant to ongoing work on scaling down shape-memory devices for use in micro-electromechanical systems. Here we present a first-principles density functional study of the structural energetics of NiTi. Surprisingly, we find that the reported B19' structure of NiTi is unstable relative to a base-centred orthorhombic structure that cannot store shape memory at the atomic level. However, the reported structure is stabilized by a wide range of applied or residual internal stresses. We propose that the memory is stored primarily at the micro-structural level: this eliminates the need for two separate mechanisms in describing the two-way shape-memory effect.
形状记忆合金（SMA）是一类独特的金属合金，在经历大变形后，加热时能恢复其原始形状。在形状记忆合金的众多实际应用中，最常用的材料是镍钛合金（镍钛诺）。目前仍缺乏对镍钛合金形状记忆效应的完整原子级理解，这一问题与当前为微机电系统缩小形状记忆装置的研究工作尤为相关。在此，我们展示了对镍钛合金结构能量学的第一性原理密度泛函研究。令人惊讶的是，我们发现所报道的镍钛合金B19'结构相对于一种不能在原子水平存储形状记忆的底心正交结构是不稳定的。然而，所报道的结构通过广泛的外加或残余内应力得以稳定。我们提出，记忆主要存储在微观结构层面：这消除了在描述双向形状记忆效应时需要两种单独机制的需求。
