We study a system of classical particles in two dimensions interacting through an isotropic pair potential that displays a martensitic phase transition between a triangular and a rhomboidal structure upon the change of a single parameter. Previously it was shown that this potential is able to reproduce the shape memory effect and super-elasticity, among other well known features of the phenomenology of martensites. Here we extend those previous studies and describe the development of the more subtle two-way shape memory effect. We show that in a poly-crystalline sample, the effect can be associated to the existence of retained martensite within the austenite phase. We also study the case of a single crystal sample where the effect is associated to particular orientations of the dislocations, either induced by training or by an ad hoc construction of a starting sample.
How to enable bulk-like martensitic transformation in epitaxial films
本研究致力于不同的衬底和缓冲层材料的影响，在溅射沉积外延形状记忆Heusler合金的马氏体相变。为此，磁热Heusler合金Ni-Co-Mn-Al \cite{Teichert2015b}在MgO（001）、MgAl $_{2}$ O $_{4}$（001）和MgO（001）/V衬底上生长，这些衬底表现出与$-1.2\%$和$3.6\%$之间的Ni-Co-Mn-Al的晶格失配。由温度依赖的X射线衍射测量结果表明，形状记忆Heusler膜的最佳缓冲层不是具有最小晶格失配的缓冲层，而是具有最小杨氏模量和适度失配的缓冲层，因为弹性缓冲层可以在Heusler层的马氏体相变期间变形。此外，适度的晶格失配引起的外延应变不会显着改变马氏体相变温度。
Tunability of martensitic behavior through coherent nanoprecipitates and other nanostructures
分子动力学模拟结果表明，共格析出相对Ni $_{63}$ Al $_{37}$合金的马氏体相变有显著影响。由非马氏体Ni $_{50}$ Al $_{50}$组成的沉淀物改变了支配相变的自由能景观，并导致热滞后的显著降低，而相变应变的代价非常小，并且改变了相变温度。重要的是，本文表明，自由能景观工程是可能的纳米结构可能通过标准的冶金加工路线。探讨了纳米沉淀体系中原子级成核和转化机制，并与外延纳米层压材料和纳米线进行了比较。模拟揭示了三种不同的制度的转变机制和马氏体纳米结构的非马氏体相的体积分数的函数。自由能景观工程是普遍适用的，并可能有助于设计新的记忆合金与新的性能，如在室温下操作的轻质合金。
Ferromagnetic interactions and martensitic transformation in Fe doped Ni-Mn-In shape memory alloys
采用差示扫描量热法、磁化强度、电阻率、X射线衍射（XRD）和EXAFS研究了Fe掺杂的Ni-Mn-In磁性记忆合金的结构、磁性和马氏体性能。虽然Ni $_{2}$ Mn In $_{1-x}$ Fe $_{x}$（$0 \le x \le 0.6$）合金是铁磁性的和非马氏体的，但是Ni $_{2}$ Mn $_{1.5} $ In $_{1-y}$ Fe $_{y}$和Ni $_{2}$ Mn $ _{1.6} $ In $_{1-y}$ Fe $_{y}$中的马氏体转变温度在较高Fe浓度急剧降低之前对于较低Fe浓度（$y \le 0.05$）增加。XRD分析揭示了在室温下Ni $_{2}$ Mn In $_{1-x}$ Fe $_{x}$中存在立方和四方结构相，四方相含量随着Fe掺杂而增加。尽管这些Fe掺杂合金中Mn和Ni周围的局部结构与马氏体富锰Ni-Mn-In合金相似，但铁磁相互作用的存在和Fe诱导的结构无序会影响Mn-Ni-Mn反铁磁相互作用，从而抑制这些Fe掺杂合金中的马氏体转变。
We describe a novel approach for the rational design and synthesis of self-assembled periodic nanostructures using martensitic phase transformations. We demonstrate this approach in a thin film of perovskite SrSnO3 with reconfigurable periodic nanostructures consisting of regularly spaced regions of sharply contrasted dielectric properties. The films can be designed to have different periodicities and relative phase fractions via chemical doping or strain engineering. The dielectric contrast within a single film can be tuned using temperature and laser wavelength, effectively creating a variab…
Superelastic shape-memory alloys (SMAs) are unique smart materials with a considerable energy dissipation potential for dynamic loadings with varying strain-rates. The energy dissipation depends on the latent heat generated by the austenitic-martensitic transformation and the convection of that heat. Due to the thermomechanical coupling, the martensitic nucleation stress level and thus the propagation of martensitic phase fronts strongly depends on the material temperature. High strain-rate interferes with the release of the latent heat to the environment and determines quantity, position and …
The inverse magnetocaloric effect (MCE) in Ni-Mn-based Heusler compounds occurs during the magnetostructural transition between low-temperature, low-magnetization martensite and high-temperature, high-magnetization austenite. In this study, we analyze the metamagnetic transformation of a $Ni_{49.8}Mn_{35}In_{15.2}$ compound by simultaneous adiabatic temperature change and strain measurements in pulsed magnetic fields up to 10 T. We observe an adiabatic temperature change of -10 K and a strain of -0.22 % when the reverse martensitic transition is fully induced at a starting temperature of 285 K…
Effect of the temperature and magnetic field induced martensitic transformation in bulk Fe$_{45}$Mn$_{26}$Ga$_{29}$ alloy on its electronic structure and physical properties
研究了温度和磁场诱发马氏体相变（MT）对Fe $_{45.2}$ Mn $_{25.9}$ Ga $_{28.9}$ Heusler合金电子结构和某些物理性质的影响。{根据DSC、磁性和输运测量的实验结果，在没有外部磁场的情况下，在194 $\leq T \leq$-328 K温度范围内发生直接和反向马氏体相变，滞后高达$ΔT \approx$ 100 K，定义为$ΔT$ = $A_{f,s}$ - $M_{s,f}$，其中$A_{f,s}$和$M_{s,f}$是直接和反向马氏体相变的临界温度。$μ_{0}H$ = 5 T的外部磁场导致MT温度的高温偏移。} MT从母奥氏体L_2PDMATHABMV相转变为马氏体四方畸变L_2PDMATHABMV相（即，e.到L1 $_{0}$）引起合金电子结构的显著变化、合金磁化强度的急剧增加、合金电阻率的降低以及电阻率温度系数的符号从负到正的反转。同时，实验确定的光学性质的Fe $_{45.6}$ Mn $_{25.9}$ Ga $_{28.9}$ Heusler合金在奥氏体和马氏体状态下看起来相当相似，在微观性质上有明显的不同，这可以从第一原理计算得出结论。实验观察到的合金的物理性能的变化进行了讨论的奥氏体和马氏体相的电子结构。
Determination of the vibrational contribution to the entropy change at the martensitic transformation in Ni-Mn-Sn metamagnetic shape memory alloys: A combined approach of time-of-flight neutron spectroscopy and ab-initio calculations
We present a unifying description for the martensitic transformation of steel that accounts for important experimentally observable features of the transformation namely, the Neumann bands, the interfacial (habit) plane between the transformed and untransformed phases and their orientation relationship (OR). It is obtained through a simple geometric minimization of the total distance traveled by all the atoms from the austenite (FCC or $γ$) phase to the martensite (BCC or $α$) phase, without the need for any explicit energy minimization. Our description unites previously proposed mechanisms bu…
Using classical molecular dynamics simulations, we study austenite to ferrite phase transformation in iron, focusing on the role of interface morphology. We compare two different morphologies; a \textit{flat} interface in which the two phases are joined according to Nishiyama-Wasserman orientation relationship vs. a \textit{ledged} one, having steps similar to the vicinal surface. We identify the atomic displacements along a misfit dislocation network at the interface leading to the phase transformation. In case of \textit{ledged} interface, stacking faults are nucleated at the steps, which hi…
An original thermodynamically consistent large strains-based multiphase phase-field (PF) approach of Ginzburg-Landau type is developed for studying the grain boundary (GB)-induced martensitic transformations (MTs) in polycrystalline materials at the nanoscale considering the structural stresses within the interfaces. In this general PF approach, N independent order parameters are used for describing the austenite (A)<->martensite (M) transformations and N(>1) martensitic variants, and another M independent order parameters are considered for describing M(>1) grains in the polycrystalline sampl…
Finely Tunable Thermal Expansion of NiTi by Stress-Induced Martensitic Transformation and Thermomechanical Training
Korea Advanced Institute of Science and Technology（韩国科学技术院）；Massachusetts Institute of Technology（麻省理工学院）；Korea University（高丽大学）；Inha University（仁荷大学）；University of Stuttgart（斯图加特大学）
