The Role of Supercompatibility on the Fatigue of Shape Memory Alloys

超相容性对形状记忆合金疲劳的作用

• 批准号: 413288478
• 负责人: Professor Dr.-Ing. Eckhard Quandt
• 金额: --
• 依托单位: Lehrstuhl für Anorganische Funktionsmaterialien
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2019
• 资助国家: 德国
• 起止时间: 2018-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/413288478?language=en
• 关键词: Role; Supercompatibility; Fatigue; Shape; Memory

Shape memory alloys (SMAs) show two distinct properties that are attractive for many applications. First, the shape memory effect is the basis for many solid-state actuators, which relies on a reversible, thermally induced, high energy density phase transformation between austenite and martensite. Second, they exhibit superelasticity used for example in self-expanding medical implants or in elastocaloric cooling, which is based on a reversible, stress-induced austenite-martensite phase transformation. These first order phase transformations with large eigenstrains in both cases result in large work output and large enthalpy changes. Their reversibility is aided by the compatibility of the two phases. Essential for the implementation of SMAs in new devices is their fatigue characteristics, especially for high-cycle applications. In general, fatigue concerns two aspects: functional fatigue, which describes the cycle-dependent changes of their functional properties and structural fatigue, which refers to the integrity of the material. Commonly, both types of fatigue are closely interconnected.In our previous work we have laid out what we believe are the most important factors governing functional and structural fatigue in stress-induced phase transformations (superelasticity) in shape memory alloys: Crystallographic compatibility, grain size (that was well known) and precipitation. We have shown that, if compositions are tuned so that all three of these factors are fulfilled, alloys with unprecedented resistance to functional fatigue are possible. However, our results have revealed that one or more of these factors can be compromised a little and still remarkable functional fatigue is achieved. This is a very important finding as the perfect crystallographic compatibility – the so-called supercompatibility -- is a very restrictive condition which was up to now only found to be almost ideally fulfilled in only two specific alloys. For example, alloys satisfying supercompatibility to high accuracy have exceptional resistance to functional fatigue, but so do alloys that satisfy these compatibility conditions only approximately, but that have small grain size and a favorable array of fine coherent precipitates. Establishing this as a general finding would significantly increase the possibility to identify ultra-low fatigue compositions thus offering a wider selection to meet other criteria as e.g. transformation temperatures and strain or biocompatibility.Thus, our main objectives are: to verify the influence of the different factors, to determine the required accuracy in satisfying this supercompatibility and thus to derive directions for a future search of ultra-low fatigue SMAs. These objectives will be applied here in the context of metallic SMAs, although it is expected that they should be applicable to broad classes of solid-solid phase transformations.

形状记忆合金（sma）表现出两种不同的特性，在许多应用中具有吸引力。首先，形状记忆效应是许多固态驱动器的基础，它依赖于可逆的、热诱导的、高能量密度的奥氏体和马氏体之间的相变。其次，它们表现出超弹性，例如用于自膨胀医疗植入物或弹性热冷却，这是基于可逆的，应力诱导的奥氏体-马氏体相变。在这两种情况下，具有大特征应变的一阶相变导致大的功输出和大的焓变。它们的可逆性得益于两相的相容性。在新器件中实现sma的关键是它们的疲劳特性，特别是在高周期应用中。一般来说，疲劳涉及两个方面：功能疲劳和结构疲劳，前者描述的是材料的功能特性随循环的变化，后者指的是材料的完整性。通常，这两种类型的疲劳是紧密相连的。在我们之前的工作中，我们已经列出了我们认为在形状记忆合金的应力诱导相变（超弹性）中控制功能和结构疲劳的最重要因素：晶体相容性，晶粒尺寸（众所周知）和沉淀。我们已经证明，如果调整成分，使这三个因素都得到满足，具有前所未有的抗功能性疲劳的合金是可能的。然而，我们的研究结果表明，这些因素中的一个或多个可以稍微妥协，但仍然可以实现显着的功能性疲劳。这是一个非常重要的发现，因为完美的晶体相容性——所谓的超相容性——是一个非常有限的条件，到目前为止，只发现在两种特定的合金中几乎理想地满足了这种条件。例如，满足高精度超相容性的合金具有优异的抗功能疲劳性能，但仅近似满足这些相容性条件，但具有小晶粒尺寸和良好的细相干析出物阵列的合金也是如此。将这一发现确立为一般发现将显著增加鉴定超低疲劳成分的可能性，从而提供更广泛的选择，以满足其他标准，例如转化温度和应变或生物相容性。因此，我们的主要目标是：验证不同因素的影响，确定满足这种超相容性所需的精度，从而为未来寻找超低疲劳sma提供方向。这些目标将在金属sma的背景下应用，尽管预计它们应该适用于广泛类别的固-固相转变。