形状记忆合金弹热效应研究进展

Elastocaloric Effects in Shape Memory Alloys:a Review and New Perspectives

中文关键词: 弹热效应 形状记忆合金 马氏体相变 超弹性 Ni-Ti合金 Ni-Mn-Ga合金

英文关键词: elastocaloric effect (eCE), shape memory alloys (SMAs), martensitic transformation, superelasticity, Ni-Ti alloy, Ni-Mn-Ga alloy

中文摘要:

      传统的气体压缩制冷技术已不能满足人类对环保节能的要求,新型制冷技术的开发近年来受到了越来越多的关注。与传统气体压缩制冷技术相比,固体制冷技术效率高、对环境友好,引起材料科学界的广泛关注。其原理是通过改变材料的外场环境,如磁场、电场或应力场,使材料的性质(结构、磁矩等)发生改变,从而产生各种热效应,即磁热效应、电热效应、机械热效应(弹热效应、压热效应)。研发具有高的热效应、宽的工作温度范围和性能稳定的室温固体制冷材料是提升固态制冷技术的关键。其中,利用形状记忆合金(SMAs)在单轴循环应力下诱发的弹热效应制冷是目前最有前景的固体制冷技术之一。 弹热效应(Elastocaloric effect, eCE)是利用形状记忆合金马氏体相变过程中产生的潜热,在应力诱发马氏体相变和逆相变过程中,材料放出和吸收相变潜热,借助制冷循环装置即可实现固体制冷。在研究过程中,弹热制冷展现出很多优点,如大而可逆的绝热温变、简单的应力驱动方式、超宽的温度适用范围等。但现阶段发现的弹热材料也存在疲劳寿命短、滞后损耗大和应变分布不均匀等问题。2014年,美国能源部将弹热制冷列为17种替代气体压缩制冷的新技术之首,推荐为最有希望发展的固体制冷模式。 近年来,科学家在室温附近诸多形状记忆合金的马氏体相变及其他材料的固态相变中测量出巨大的弹热效应,如Cu-Zn-Al、Ti-Ni-(Cu)、Fe-Pd、Ni-Mn-Sn-(Cu)、Ni-Mn-In-Co等。衡量弹热效应大小的参数主要有绝热温变ΔTad和等温熵变ΔSiso,可以通过直接或间接的方法获得。利用形状记忆合金的应力-应变曲线和麦克斯韦方程可以计算材料的等温熵变ΔSiso,间接地表征弹热效应的大小。而鉴于弹热效应驱动方式简单,更简便的衡量方法是直接测量绝热温变ΔTad,即使用精密的测温设备测量材料相变前后的温度。这种方法不仅可以表征弹热效应的大小,还能了解其热效应产生过程中的细节,如弹热过程中材料温度变化的位置、趋势等。 本文综述了传统记忆合金(Cu基、Ni-Ti基、Fe基)和新型铁磁性记忆合金(主要是Ni-Mn基)弹热效应的研究进展,分析了不同类型记忆合金在弹热制冷方面的优缺点,最后对弹热制冷材料的发展进行了展望。

英文摘要:

      The traditional gas-compression refrigeration technology can no longer meet the requirements of human society for environmental protection and energy conservation. The development of new refrigeration technology has drawn increasingly growing attention in recent years. Compared to the traditional gas-compression refrigeration technique, solid-state cooling technology has aroused extensive interests owing to the high efficiency and environmental friendliness. The principle of solid-state cooling is to change the environment of external field (such as magnetic field, electric field and stress field) of a material, and change the properties (structure, magnetic moment, etc.) of the material accordingly, thus produce the corresponding caloric effects, namely magnetocaloric effect, electrocaloric effect and mechanocaloric effect (elastocaloric effect, barocaloric effect). The key for promoting the solid-state cooling technology lies in the development of room temperature caloric materials that exhibit giant entropy change, wide working temperature interval and high operation stability. Among them, the elastocaloric cooling based on the elastocaloric effect (eCE) induced by uniaxial cyclic stress in shape memory alloys (SMAs) is one of the most promising solid-state cooling technology. The eCE in SMAs originates from the martensite transformation enthalpy, i.e. in the process of stress-induced martensite transformation and inverse transformation, the material releases and absorbs the latent heat of phase transformation, and the solid refrigeration can be realized by means of refrigeration cycle device. In the course of the study, elastocaloric cooling technology presemts many advantages, including large and reversible adiabatic temperature change, simple stress-driven method and wide application range of temperature. However, the eCE materials are still exist problems like short fatigue life, large hysteresis loss and uneven strain distribution. In 2014, the elastocaloric cooling technology was ranked as the first of 17 new alternative technologies for gas-compression cooling by U.S. Department of Energy, which has been recognized as the most promising cooling systems. Rencntly, scientists have measured large caloric effects in many SMAs near room temperature, such as Cu-Zn-Al, Ti-Ni-(Cu), Fe-Pd, Ni-Mn-Sn-(Cu), Ni-Mn-In-Co. The adiabatic temperature change ΔTad and the isothermal entropy change ΔSiso are the main measuring parameters of eCE, which can be obtained by direct or indirect methods. ΔSiso can be calculated by the stress-strain curve of SMAs and Maxwell’s equation, which can characterize the eCE indirectly. Moreover, due to the simple driving method of the eCE, a more convenient method is measuring the ΔTad directly, which means measure the temperature before and after martensite transformation by a precise temperature measuring equipment. This method can not only characterize the magnitude of eCE directly, but also acquire the changing details in the process of eCE, like the trend or location of temperature changes in eCE materials. In this article, the research progress of eCE in traditional SMAs (Cu-, Ni-Ti- and Fe-based) and ferromagnetic SMAs (Ni-Mn-based) are reviewed. The pros and cons of various SMAs for eCE are analyzed. Finally, the development prospects of elastocaloric materials is proposed.