Ni52 Mn23Ga24.5 Sm0.5合金的马氏体相变和磁致伸缩性能

研究了多晶Ni52 Mn23 Ga24．合金添加微量的稀土元素Sm后，对合金的马氏体相变和磁致伸缩性能的影响。结果发现，微量稀土元素Sm的掺入，降低了合金的马氏体相变温度和居里温度，但并未改变合金的晶体结构，同时由于晶粒细化作用，使合金室温时的磁致应变性能下降。     

粘结NiMnGaSi合金的结构、相变和大磁致应变研究

采用还原扩散方法制备了NiMnGaSi合金粉末,并粘结成磁体.磁测量表明粘结磁体的马氏体相变开始温度MS为308 K,居里温度TC为358 K.磁致应变测量发现粘结NiMnGaSi磁体在300 K、0.7 T的磁场下具有0.56%大磁致应变.     

织构取向Ni_(54)Mn_(21)Ga_(25)合金的相变和磁致应变

用定向凝固方法制备Ni54Mn21Ga25取向多晶合金。在292K下测量了样品的磁致伸缩应变回线,结果表明:加正反方向磁场时,磁致伸缩应变回线基本对称,并存在磁致伸缩跳跃现象,饱和磁致应变约为-1.06×10-3,对应的饱和磁场为0.4T。差示扫描量热仪测量显示,马氏体相变起始温度Ms为334K,结束温度Mf为320K;逆马氏体相变起始温度As为333K,结束温度Af为353K。阻温特性测量给出样品的居里温度约350K左右。     

真空磁场热处理对Tb0.3Dy0.7Fe1.95合金磁致伸缩性能的影响

研究了磁场热处理对Tb0.3Dy0.7Fe1.95多晶合金磁致伸缩性能的影响.将定向凝固得到的多晶合金,在真空条件下,加热到居里点附近不同温度,在加磁场下保温一定时间后冷却到室温,测量其磁致伸缩系数,并且进行X衍射分析.实验结果表明,在稍低于居里点的温度,沿垂直于棒的轴线加磁场保温一定时间后冷却,合金的磁致伸缩系数明显提高,沿样品棒轴线的晶体取向有一定程度的改变.     

铸态及快淬态Ni50Mn26Ga19Fe5合金的磁致应变

研究了铸态及快淬Ni50Mn26Ga19Fe5掺杂合金的磁致应变性能.结果表明,掺Fe的Ni-Mn-Ga合金也具有典型的热弹性马氏体相变过程和磁转变过程,但铸态合金的结构为7层调制型马氏体(7M),而快淬合金的结构为14层调制型马氏体(14M).铸态合金最大磁致应变可达0.1%,快淬薄带合金最大磁致应变只能达到0.0095%.Ni50Mn26Ga19Fe5铸态合金比快淬合金有更大的磁致应变,说明掺杂元素Fe在Ni-Mn-Ga合金中的作用较为复杂.     

Tb0.5Dy0.5（Fe1-x）1.91（x=0～0.15）合金的温度性能研究

研究了Mn元素掺杂及热处理工艺对超磁致伸缩材料Tb0.5Dy0.5（Fe1-x）1.91（x=0～0.15）合金温度性能的影响，实验结果表明Mn掺杂对该材料居里温度影响较大，随Mn掺杂量的增加居里温度降低：在无预压应力时，Mn掺杂提高了合金的低温、低场磁致伸缩应变性能；热处理工艺对进一步提高磁致伸缩性能无明显作用。     

浇铸态Ni50Mn27Ga23合金中的马氏体相变和磁应变

用感应溶炼并浇铸制备了名义成份为Ni50Mn27Ga23的合金。用交流磁化率测定了合金的相变温度和居里温度，用动态电阻应变仪测试了合金在不同温度及不同磁场强度下的相变应变和磁诱导应变。研充的结果表明：相变应变具有各向异性，外磁场可显著增大相变应变；不同温度下磁场诱导的应变具有不同的特征，温度越低磁诱导应变越大，但使应变饱和所需的磁场也越高，在个别温度点伴随应变突变。磁场的训练不会显著提高磁诱导应变，相反可使可恢复应变减少。     

铁磁形状记忆合金Ni2MnGa多晶的磁-力学特性

对外加磁场、应力场共同作用下的铁磁形状记忆合金多晶的磁-力学特性进行了实验测试与研究,分别获得了两种组分Ni52Mn27Ga21和Ni54Mn25Ga21多晶样品在不同磁场倾角下、不同预加应力下的磁化曲线和磁滞回线;以及不同外加磁场及磁场倾角下的应力-应变曲线和磁致应变曲线等磁-力学特性曲线.结果表明铁磁形状记忆合金多晶沿样品轴向所测的饱和磁化强度随磁场倾角的增大而减小,施加预应力并不显著影响样品的磁化曲线和磁滞回线;各种角度时不同磁场对两种多晶样品的应力-应变关系影响均很小.     

外磁场对Ni-Mn-Ga磁性形状记忆合金相变应变及显微组织的影响

研究了外磁场对Ni52Mn24.6Ga23.4(%,原子分数)单晶马氏体相变及其相变应变的影响,并对磁场增强相变应变的微观机制进行了探讨。研究结果表明无外加磁场时,NiMnGa合金发生马氏体相变时可产生约0.3%的收缩形变,沿单晶[100]方向施加外磁场,其相变应变随磁场的增加而呈近线性增加。当外磁场强度为6.37×105A/m时,应变量达到最大值(3.5%)。磁场作用下冷却形成的马氏体虽然孪晶亚结构不变,但自协作组态消失,并伴随有孪晶板条的增厚。磁场对马氏体相变应变的增强效应来自于磁场作用下的马氏体变体的择优取向。     

预应变对铝基体中复合的TiNi合金丝马氏体逆相变的影响

采用示差扫描热分析(DSC)、X射线衍射(XRD)和扫描电子显微分析(SEM)等方法,研究了预应变对铝基体中复合的TiNi形状记忆合金丝的马氏体逆相变的影响.结果表明,预应变的TiNi丝发生两种逆相变,一种是热致马氏体(TIM)的逆相变,另一种是应力诱发马氏体(SIM)的逆相变.预应变样品的TIM逆相变的起始温度与未预应变样品的基本相同.SIM逆相变的起始温度随预应变的增大而升高.TIM和SIM逆相变的分数随预应变的增大而减少.     

磁性形状记忆合金研究进展

磁性形状记忆合金是上世纪90年代开始出现的一类新型金属功能材料。这类合金兼具热弹性马氏体相变和磁性转变,其形状记忆效应可以由磁场控制。此外这类合金还具有磁阻、磁热等丰富的物理效应,因而一直是近期研究热点。首先介绍了磁性形状记忆合金的3个基本特征,即马氏体相变与磁性转变、磁场驱动孪晶再取向和磁场诱发相变。然后分别对Ni基、Co基和Fe基磁性形状记忆合金的研究现状进行了评述。最后展望了磁性形状记忆合金的发展趋势。     

粘结Ni52Mn24.4Ga23.6磁体研究

真空感应熔炼法制备了多晶Ni52Mn24.4Ga23.6合金,对多晶合金进行了DSC分析和显微组织观察;采用粉末压缩压制的方法制备了粘结Ni52Mn24.4Ga23.6磁体;通过X射线衍射分析,讨论了外应力场和磁场对粘结Ni52Mn24.4Ga23.6磁体马氏体相变的影响;测量了粘结Ni52Mn24.4Ga23.6磁体在磁场下的磁诱发应变.结果表明:室温时粘结磁体在1.2T的磁场下能产生150ppm的饱和伸长应变.     

Ni2 In型六角MM’X铁磁马氏体相变材料及其研究进展

六角结构MM’X材料是一类潜在的新型磁相变功能材料。基于磁性马氏体相变,它们表现出优异的磁驱马氏体相变效应和磁热效应。介绍了MM’X材料的基本结构、磁性和研究历史,综述了近年来人们对其磁场响应性能的研究进展。阐述了人们在探索和提升代表性体系MnNiGe,MnCoGe的物理性能过程中的思想、方法和结果,重点探讨了人们对磁共结构耦合转变的调控和实现,尤其是顺磁-铁磁型马氏体相变所需要的居里温度窗口的构建。展望了MM’X材料潜在的磁性功能应用和优势。     

Excellent mechanical properties and large magnetocaloric effect of spark plasma sintered Ni-Mn-In-Co alloy

The Ni43.75Mn37.5In12.5Co6.25 alloy was obtained by using the spark plasma sintering (SPS) technique.The martensitic transformation,magnetic and mechanical properties of the SPS alloy were investigated.Key findings demonstrate that the martensitic transformation temperature of this alloy is about 10 K lower than that of the as-cast one.Both SPS and as-cast alloys show a 7 layered modulated martensite (7M) at room temperature.The compressive fracture strength and strain of the SPS alloy increase by 176.92％ and 33.33％ compared with the as-cast alloy,achieving 1440 MPa and 14％,respectively.The maximum magnetic entropy change △Sm is 17.1 J kg-1 K-1 for the SPS alloy at the magnetic field of 5 T.     

Martensitic Transformation and Magnetic-Field-Induced Strain in Magnetic Shape Memory Alloy NiMnGa Melt-Spun Ribbon

A magnetic shape memory alloy with nonstoichiometric Ni50Mn27Ga23 was prepared by using melt-spinning technology. The martensitic transformation and the magnetic-field-induced strain (MFIS) of the polycrystalline melt-spun ribbon were investigated. The experimental results showed that the melt-spun ribbons underwent thermal-elastic martensitic transformation and reverse transformation in cooling and heating process and exhibited typical thermo-elastic shape memory effect. However the start temperature for martensitic transformation decreased from 286 K for as-cast alloy to 254 K for as-quenched ribbon and Curie temperature remains approximately constant. A particular internal stress induced by melt-spinning resulted in the formation of a texture structure in the ribbons, which made the ribbons obtain larger martensitic transformation strain and MFIS. The internal stress was released substantially after annealing, which resulted in a decrease of MFIS of the ribbons.     

Ni-Mn基磁性形状记忆合金第二相的形成及其对相变和性能的影响

Ni-Mn基磁性形状记忆合金具有良好的温度场和磁场诱发的形状记忆效应、超弹性、磁热效应、磁阻效应、弹热效应、交换偏置效应等功能特性。作为一种新型多功能材料,有望应用于驱动器、传感器等多个工程领域。本文详细阐述了包含第二相的Ni-Mn基磁性形状记忆合金的研究现状,梳理和总结了第二相的形成及其对马氏体相变、功能特性和力学性能的影响,提出了一些有待解决的问题,如第二相对包括磁性形状记忆效应在内的磁功能特性的影响,并指出未来应着重于研究第二相形成与演化过程的热力学/动力学因素,对第二相进行合理调控,从而优化合金功能特性。     

快速凝固Ag-RE合金的相结构

在冷却速度为10~6K/s 的快速凝固 Ag-RE(RE=Sm,Gd,Tb,Dy,Er)合金箔试样中出现固溶度扩展和 Ag_3RE 六方结构亚稳相。在随后的时效过程中,过饱和固溶体转变为平衡固溶体,Ag_3RE亚稳相转变为 Ag_(51)RE_(14)平衡相。     

Influence of Rare-Earth Elements on ElectricalProperties of Pd

The influence of RE (RE = La, Ce. Pr. Nd, Sm, Eu, Gd. Tb. Dy, Er, Yb) additives with dilute concentrations on the electrical properties of Pd has been studied. All RE elements increase the specific resistivity (ρ) and decrease the resistance temperature coefficient (α) of Pd. and (ρ.α) Pd-RE ls equal to (ρ· α)Pd.The RE elements before Gd reduce the thermo-emf of Pd on Cu. other heavy RE enhance the thermo-emf.The experimental data of normalized Pd-0.1 at.-%RE alloys indicate that the effect of light RE additives on the specific resistivity of Pd is larger than that of heavy RE and Ce. Eu and Yb show anomalous strong effect. The valence and atomic size are main factors influencing the electrical properties.     

Characterization and properties of ferromagnetic shape memory alloys

Ni–Mn–Ga shape memory alloys are employed for applications in actuators and sensing devices. These alloys exhibit ferromagnetic shape memory effect with large reproducible strains in moderate magnetic fields. This work presents a study of the effect of composition and annealing treatment on the microstructure and magnetic properties in Mn-rich off-stoichiometric Ni–Mn–Ga alloys. Modulated martensitic structure (c/a < 1) with hierarchical twins was found at room temperature in alloys with Mn ≥ 28 at.% whereas the alloy containing higher Ga (> 22 at.%) revealed austenitic structure at room temperature. Ferromagnetic nature of the alloys was confirmed by the magnetization curves. It is demonstrated that a maximum of 400 parts per million strain was measured in the alloy with 7 M martensitic structure at room temperature.     

Estimation on Magnetic Refrigeration Material （Gd1-xREx）5Si4 （RE=Dy, Ho）

A systematic (Gd1-xREx)5Si4 (RE=Dy, Ho) alloys are investigated to estimate their magnetocaloric effect.The Curie points of (Gd1-xREx)Si4 alloys can tunable from 266 K to 336 K when RE=Dy, Ho; x=0～0.35 and 0～0.15, respectively, and decrease nearly linearly with increasing x. These alloys keep orthorhombic structures Ge5Sm4 and exhibit second order transition when they experience in a change magnetic field at about Curie when magnetic field changes 0～2 T. The adiabatic temperatures changes (△Tad) of these alloys at Curie points are larger than 1 K in a field change 0～1.4 T, the curve of △Tad is wide as that of Gd. The relative cooling power is about 0.8～0.9 J/cm3 when field changes 0～2 T, 55% of that of Gd. Comparing with Gd5(Si1-xGex)4, these alloys do not contain expensive element Ge, so that their cost are lower than the former. Because they could work at temperature region 260～340 K due to their Curie points can be tuned, which is an advantage comparing with Gd, these alloys are potential magnetic refrigerants working in a magnetic refrigerator with a low magnetic field at room temperatures.