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.

形状内存合金（SMA）显示了两种不同的属性，这些属性对许多应用都有吸引力。首先，形状记忆效应是许多固态执行器的基础，该固态执行器依赖于奥氏体和马氏体之间的可逆，热诱导的高能密度相变。其次，他们暴露了例如在自扩展的医疗燃料或弹性冷却中使用的超弹性，该弹性是基于可逆的，压力诱导的奥氏体 - 明星相变的。在这两种情况下，这些具有较大特征性的一阶相变，都会导致大量的工作输出和较大的焓变。它们的可逆性得到了两个阶段的兼容性。在新设备中实施SMA的必不可少的是它们的疲劳特征，尤其是对于高周期应用。通常，疲劳涉及两个方面：功能疲劳，它描述了其功能特性和结构疲劳的循环依赖性变化，这是指材料的完整性。通常，两种类型的疲劳都是紧密相互联系的。在以前的工作中，我们列出了我们认为在压力诱导的相位转换（超弹性）中的功能和结构疲劳的最重要因素：晶体学兼容性：晶体学兼容性，晶粒尺寸，晶粒尺寸（众所周知）和沉淀。我们已经表明，如果对组合物进行调整，以便满足所有这三个因素，则可以实现对功能疲劳的前所未有的合金。但是，我们的结果表明，这些因素中的一个或多个可能会损害一点功能疲劳。这是一个非常重要的发现，因为完美的晶体学兼容性 - 所谓的超级稳定性 - 是一个非常限制的条件，到目前为止，仅在仅在两种特定的合金中就可以很好地实现。例如，满足高精度超准确性的合金具有出色的抗性疲劳性，但是仅满足这些兼容条件的合金也大约满足这些兼容性条件，但晶粒尺寸且良好的优质相干珍贵的珍贵阵列。将其确定为一般发现将显着增加鉴定超低疲劳组合物的可能性，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，以确定满足这种超级稳定性的所需准确性，从而为未来搜索超低疲劳SMA的搜索提供方向。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的固体相变。