磁控溅射法制备铁磁形状记忆合金Ni—Mn—Ga薄膜的力学性能研究

Ni-Mn-Ga是一种磁致伸缩材料、它兼具形状记忆效应和磁致伸缩效应等多种功能特点,具有响应频率高,变相量大的优点.而PbZrTiO3(PZT)是一种压电陶瓷,具有力-电转换的功能,而且也具有较高的响应频率.为实现磁-力-电的快速转换,本文使用ECR磁控溅射方法在PZT压电陶瓷片上制备出了Ni-Mn-Ga薄膜.并研究了不同溅射功率和热处理条件对薄膜的组织形貌、成分、表面粗糙度及薄膜硬度的影响.SEM断面形貌显示Ni-Mn-Ga薄膜为柱状生长模式;AFM三维形貌显示Ni-Mn-Ga薄膜生长致密,表面粗糙度随着溅射功率的增大而增大;Ni-Mn-Ga薄膜的硬度和弹性模量随退火温度的升高而增大.     

Bending properties of epoxy resin matrix composites filled with Ni-Mn-Ga ferromagnetic shape memory alloy powders

Two types of epoxy resin matrix composites filled with Ni-Mn-Ga ferromagnetic shape memory alloy powders, with and without magnetic field during curing, were prepared, aiming to create anisotropic and isotropic alignments of the Ni-Mn-Ga particles. The bending properties of the composites are found to be significantly influenced by the distribution of Ni-Mn-Ga particles in the epoxy matrix. The composites without magnetic field during curing exhibit larger bending strength and fracture strain than the composites with magnetic field during curing. The fractography reveals that the Ni-Mn-Ga particle chains formed in the composites with magnetic field during curing facilitate the initiation and propagation of cracks, thus weakening the bending properties.     

Ni52.5Mn23.5Ga23.6Tb0.4磁性形状记忆合金马氏体相变和磁感生应变的研究

研究多晶合金Ni52.5Mn23.5Ga24的马氏体相变特征和磁感生应变性能,分析了稀土元素Tb对合金马氏体相变和磁性能的影响.研究结果表明,添加Tb使合金Ni52.5Mn23.5Ga24的马氏体相变温度提高到室温以上,并且降低了合金的温度滞后,在一定压力的作用下合金磁感生应变值增大.     

Ni52Mn21+xGa27-x(x=0-5)磁性形状记忆合金的相变

研究了非化学计量成分的多晶Ni52Mn21+xGa27-x(x=0-5)系列合金的热弹性马氏体相变和磁相变.合金的马氏体相变温度Ms随Mn含量的增加而升高,当x＞4时,Ms已经升高到室温以上,而马氏体相变滞后△T随z的增大而减小;合金的磁相变温度TC随z增加而升高,但变化范围不大,在z＞2后,Tc保持在348 K左右.实验获得了一种具有实用前景的合金成分--Ni52Mn25Ga23合金,其马氏体相变温度在室温以上,相变滞后仅为5 K.     

Large low-field magnetocaloric effect in a directionally solidified Ni50Mn18Cu7Cu25 alloy

Magnetic refrigeration based on the magnetocaloric effect (MCE) is conceived as a promising alternative to the conventional gas compression/expansion technique. For potential applications, the magnetic refrigerants exhibiting high-performance at low field are in great need. In this work, we present large MCE obtained in a directionally solidified polycrystalline Ni₅₀Mn₁₈Cu₇Ga₂₅ alloy with the co-occurrence of magnetic transition and martensitic transformation. Such a strong magneto-structural coupling yields large magnetic entropy change of −12.8 Jkg⁻¹K⁻¹ and adiabatic temperature variation of 1.6 K at an external magnetic field change of 1.5 T. It is demonstrated that the fabrication of Ni-Mn-Ga based alloys through composition tuning and directional solidification could be an economical processing route to improve magnetocaloric properties.     

Inapplicability of the Maxwell relation for the quantification of caloric effects in anisotropic ferroic materials

Giant caloric effects were reported in elasto-, electro- and magnetocaloric materials near phase transformations. Commonly, their entropy change is indirectly evaluated by a Maxwell relation. Additionally to the well-known spurious “colossal” results near first-order phase transitions and limitations in the presence of magnetic domains, we report the fundamental failure of this approach for materials that show structural reorientations in external fields. We analyze exemplarily the magnetic shape memory alloy Ni-Mn-Ga. Application of a magnetic field causes magnetically induced reorientation of the crystal structure in the martensite phase. This results in a spurious inverse magnetocaloric effect that disappears when the measurement procedure is repeated. This failure is universal as the vector character of the applied field is not considered in the common scalar evaluation of a Maxwell relation.     

形状记忆合金弹热效应研究进展

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、TiNi-(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。     

淬速对Ni-Mn-Ga快淬合金相变的影响

采用快淬技术制备了Ni-Mn-Ga薄带合金,研究了不同淬速对Ni-Mn-Ga快淬合金相变过程的影响.结果表明,快淬合金具有典型的热弹性马氏体相变过程,但合金的马氏体相变开始温度Ms比铸态合金的有所降低,并随淬速的升高,快淬合金的Ms逐渐降低.Ni-Mn-Ga合金马氏体相变的热力学分析表明:快淬合金晶粒愈细小,Ms愈低;快淬工艺不改变合金的晶体结构;在不同淬速的快淬合金中有以(400)晶面为择优取向的织构存在.     

Role of magnetism on the martensitic transformation in Ni-Mn-based magnetic shape memory alloys

The effect of magnetism on the martensitic structural transformation has been analyzed through the evolution of the transformation temperatures of several Ni-Mn-Ga and Ni-Mn-In alloys subjected to high-temperature quenching and post-quench annealing thermal treatments. It is found that the atomic order variations associated with the thermal treatments affect the structural transformation in different ways depending on the character of the magnetic ordering in the austenitic and the martensitic phases. In particular, regardless of composition, the variation in the atomic order affects the martensitic transformation temperature only in those alloys in which at least one of the structural phases show magnetic order at the transformation temperature, whereas those transformations taking place between paramagnetic phases remain unaffected. The observed behaviors are explained in terms of the effect of the magnetic exchange coupling variations on the free energy difference between austenite and martensite. The results confirm the key role of magnetism in the martensitic transformation.     

Ni48Mn33Ga18Tb1合金的马氏体相变和磁性形状记忆效应

本文研究了 Ni48Mn3 3 Ga1 9合金添加微量的稀土元素 Tb后 ,对合金的马氏体相变、磁致应变性能及抗弯性能的影响 ,发现合金的马氏体相变温度、磁致应变值有所下降 ,而机械抗弯强度有显著提高。