Molecular dynamics simulation study of microstructure evolution during cyclic martensitic transformations
Molecular dynamics simulation study of microstructure evolution during cyclic martensitic transformations
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DOI：
10.1016/j.jmps.2011.05.009
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发表时间：
2011-09-01
影响因子：
5.3
通讯作者：
Ackland, Graeme J.
中科院分区：
文献类型：
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作者：
Kastner, Oliver;Eggeler, Gunther;Ackland, Graeme J.
形状记忆合金(SMA)表现出许多用平衡热力学难以解释的特征，包括相变滞后和高度对称相中的“反向”形状记忆。加工可以改变这些特征：重复骑行可以在改变滞后量等功能属性的同时，对反向形状记忆效果进行“训练”。这些效应很可能是由于局部缺陷的形成，这些可以用原子方法来研究。在这里，我们用二维Lennard-Jones模型对这种行为进行了分子动力学模拟研究。我们的原子模型显示了一个对称性破缺，从高温、熵稳定的类奥氏体相到低温类马氏体相的相变。模拟表明，该模型材料中的相变通过非扩散形核和生长过程进行，并产生明显的微观组织。我们观察到在正向和反向相变过程中产生了持久的晶格缺陷，这些缺陷在随后的相变过程中作为形核中心。这些缺陷干扰了转化的时间和空间进程，从而影响了后续的产品形态。在循环变换过程中，我们观察晶格缺陷的积累，以建立新的微结构元素，这些元素代表了对以前形态的记忆。这些新元素是自组织的，它们为模型材料中的可逆形状记忆效应提供了基础。(C)2011爱思唯尔有限公司。保留所有权利。
Shape memory alloys (SMA) exhibit a number of features which are not easily explained by equilibrium thermodynamics, including hysteresis in the phase transformation and "reverse" shape memory in the high symmetry phase. Processing can change these features: repeated cycling can "train" the reverse shape memory effect, while changing the amount of hysteresis and other functional properties. These effects are likely to be due to formations of localised defects and these can be studied by atomistic methods. Here we present a molecular dynamics simulation study of such behaviour employing a two-dimensional, binary Lennard-Jones model. Our atomistic model exhibits a symmetry breaking, displacive phase transition from a high temperature, entropically stabilised, austenite-like phase to a low temperature martensite-like phase. The simulations show transformations in this model material proceed by non-diffusive nucleation and growth processes and produce distinct microstructures. We observe the generation of persistent lattice defects during forward-and-reverse transformations which serve as nucleation centres in subsequent transformation processes. These defects interfere the temporal and spatial progression of transformations and thereby affect subsequent product morphologies. During cyclic transformations we observe accumulations of lattice defects so as to establish new microstructural elements which represent a memory of the previous morphologies. These new elements are self-organised and they provide a basis of the reversible shape memory effect in the model material. (C) 2011 Elsevier Ltd. All rights reserved.