Thermodynamic aspects of shape memory alloys
Thermodynamic aspects of shape memory alloys
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DOI：
10.1016/s0895-7177(01)00134-0
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发表时间：
2001-12-01
影响因子：
--
通讯作者：
Seelecke, S
中科院分区：
文献类型：
--
作者：
Müller, I;Seelecke, S
相变是一种普遍现象，它为热力学提供了一个重要的研究领域。因此，将热力学应用于形状记忆合金的相变和孪晶过程是合适的。在这篇贡献中，我们发展了一个简单的一维模型的热力学和统计热力学的一个简单的一维模型含有奥氏体相和马氏体孪晶。我们认识到，该模型允许计算自由能函数，该自由能函数预测低温时马氏体为稳定相，高温时奥氏体为熵稳定相。形状记忆合金的相变是滞后的，我们认为滞后是相间共格的结果。通过这种方式，可以将磁滞的大小与界面能联系起来，并预测相变过程中潜热的释放。相图可以在温度-变形图中构建，计算相干性对相图形状的细微变化是很有趣的。吉布斯相律不再适用于通常的形式。如何正确处理磁滞回线中的亚稳性仍然是一个谜。我们讨论了这一点，但没有解决它。我们的模型允许模拟拉伸试件对热力学输入的响应。因此，如果载荷和温度被规定为时间的函数，我们就能够计算出变形和所有相分数作为时间的函数。特别是，我们可以在载荷-变形图中模拟等温线，这些等温线表示低温下的准塑性和高温下的伪弹性。(C)2001爱思唯尔科学有限公司。保留所有权利。
Phase transitions are universal phenomena which provide an important field of study for thermodynamics. It is therefore appropriate that thermodynamics should be applied to phase transitions and twinning processes of shape memory alloys.In this contribution, we develop thermodynamics and statistical thermodynamics of a simple one-dimensional model for a crystalline body which has an austenitic phase and martensitic twins. We recognize that the model permits the calculation of a free energy function which predicts martensite as the stable phase at low temperature and austenite as an entropically stabilized phase at high temperature.The phase transitions in shape memory alloys are hysteretic, and we consider hysteresis as a consequence of coherency between the phases. In this manner, it is possible to relate the size of the hysteresis to the interfacial energy and to predict the release of latent heat during the transition.A phase diagram can be constructed in the temperature-deformation plot and it is interesting to calculate the subtle changes which coherency predicts for the shape of the phase diagram. The Gibbs phase rule no longer applies in the usual form.The proper treatment of the metastability within the hysteresis loops is still a mystery. We discuss this point but do not resolve it.Our model permits the simulation of the response of a tensile specimen to a thermodynamic input. Thus, we are able to calculate the deformation and all phase fractions as functions of time if the load and the temperature are prescribed as functions of time. In particular, we can simulate isotherms in a load-deformation diagram that represent quasiplasticity at low temperature and pseudoelasticity at high temperature. (C) 2001 Elsevier Science Ltd. All rights reserved.