NiMnGa和NiMnFeGa单晶磁感生应变的温度依赖性及孪晶界移动的能量损耗

在提拉法生长出Ni52Mn16.4Fe8Ga23.6单晶样品的基础上,测量了其相变应变和磁感生应变。与Ni52Mn24.5Ga23.5单晶样品的实验结果对比分析可知,两种材料都具有较大的自发相变应变量和磁感生应变量,但Ni52Mn16.4Fe8Ga23.6单晶的磁感生应变具有较好的温度稳定性。依据实验结果和利用热动力学原理,分别计算了两种单晶样品磁感生应变升降磁场一个循环过程中孪晶界移动的能量损耗,给出了能量损耗随温度变化的关系,结果表明磁感生应变量可定性反映一个循环过程中孪晶界移动的能量损耗。     

高温形状记忆合金Ni54Mn25Ga21相变及其形状记忆效应的研究

主要研究了马氏体相变温度Ms高于居里温度Tc的Ni54Mn25Ga21合金的相变及其单晶的形状记忆效应.采用真空电弧炉熔炼,然后用磁悬浮区熔晶体生长炉进行Ni54Mn25Ga21合金的单晶生长,成功制备了Ni54Mn25Ga21单晶.对多晶粉末样品进行了原位X射线衍射变温分析,结果表明Ni54Mn25Ga21合金具有可恢复的热弹性马氏体相变性能.对Ni54Mn25Ga21单晶进行的形状记忆效应实验结果表明,当总预应变不超过6%时,压缩变形后残留的应变可在随后的加热过程中完全回复.     

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.     

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.     

成分对多晶Ni-Mn-Ga磁性记忆合金相变行为的影响

研究了Ni50Mn25+xGa25-x和Ni50Mn29Ga21-xTbx两种成分系列磁性记忆合金的相变行为.保持Ni含量不变,增加Mn,降低Ga含量会使马氏体相变温度明显提高,同时相变滞后温区减小,居里温度基本不变.如果添加稀土元素铽、相变温度继续升高,居里温度仍然不变,材料继续保持强的铁磁性及热弹性马氏体相变的特征.     

磁控形状记忆合金Ni2MnGa的制备与性能研究

本文采用电弧熔炼的方法制备了Ni48.2Mn22.4Ga29.4磁控形状记忆合金,XRD结果表明:该合金室温为面心立方晶体结构.相转变温度分别为Mf=-11℃、Ms=1℃、As=3℃、Af=11℃.随温度的降低,磁场对应变的影响增大,在207K、5KOe下可获得2.1×10-4的应变量.预变形可以使奥氏体开始变温提高.     

粘结Ni52Mn24.4Ga23.6磁体磁诱发应变特性

制备了具有择优取向的粘结Ni52Mn24.4Ga23.6磁体,测量了其在不同温度下的磁诱发应变,并就测试温度对磁诱发应变的影响进行了探讨.结果表明:粘结磁体室温时在1.2T磁场下磁诱发应变能达到饱和,为150×10-6的伸长应变;零摄氏度时磁体则在0.6T的磁场下产生76×10-6的饱和收缩应变;零摄氏度时磁诱发应变的可逆性要明显好于室温时应变的可逆性.XRD分析表明,造成不同测试温度下粘结磁体磁诱发应变行为不同的原因可能是不同温度下合金晶体结构有所不同.     

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。     

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。     

Sb对Mn50Ni40In10合金相变及磁性的影响

研究了Sb替代部分In对铁磁性形状记忆合金材料Mn50Ni40In10相变和磁性的影响。研究表明,在掺杂后形成的Mn50Ni40In10-x Sbx系列合金中,随着Sb含量的增加,马氏体的逆相变温度逐渐升高,居里温度逐渐降低。其相变温度的升高主要归结于电子浓度和晶格体积的变化以及电子轨道的杂化作用。Sb掺杂会导致样品马氏体相和奥氏体相之间的饱和磁化强度差ΔM的变化,x<0.6的微量掺杂会使ΔM增大,x>0.6时,ΔM随着掺杂量的增加而逐渐降低甚至减为零。x=0.6的样品(Mn50Ni40In9.4Sb0.6)在20kOe的外场作用下ΔM达到74emu/g,同时在该材料中观察到了磁场驱动的马氏体到奥氏体的转变,显示出该材料作为磁驱动形状记忆材料的潜在应用前景。     

Temperature stability of magnetic field-induced strain and field-controlled shape memory effect on Ni/sub 52/Mn/sub 16.4/Fe/sub 8/Ga/sub 23.6/ single crystals

The temperature dependence of the magnetic field-induced strain (MFIS) and the field-controlled shape memory effect in Ni/sub 52/Mn/sub 16.4/Fe/sub 8/Ga/sub 23.6/ single crystals were investigated by measuring the MFIS and measuring the magnetic field-enhanced transformation strain with a field bias applied in the [001] and [010] directions of the parent phase, respectively. The results show that such material combined with the martensitic transformation can product large field-enhanced transformation strain and large MFIS. The strain accompanying the martensitic transformation is -1.61% in zero field and can be enhanced to -3.30% by a field of 960 kA/m. A MFIS of 1.04% has been induced along [001] in unstressed crystals with saturated magnetic field of 600 kA/m applied along the same direction at near martensitic transformation temperature. It was found that the MFIS is almost temperature independent; the maximum decrease of the saturated MFIS is less than 10%, from 265 K to 100 K. This well-behaved temperature response makes this alloy particularly valuable for industrial and military smart actuators and transducers. Furthermore, it was found that the direction in which the MFIS has the largest value is always the [001], namely, the growth direction of the crystals.     

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.     

Magnetic field-induced strain and magnetoelectric effects in sandwich composite of ferromagnetic shape memory Ni-Mn-Ga crystal and piezoelectric PVDF polymer

A sandwich composite consisting of one layer of ferromagnetic shape memory Ni-Mn-Ga crystal plate bonded between two layers of piezoelectric PVDF polymer film was fabricated, and its magnetic field-induced strain (MFIS) and magnetoelectric (ME) effects were investigated, together with a monolithic Ni-Mn-Ga crystal, as functions of magnetic fields and mechanical load. The load-free dc- and ac-MFISs were 0.35 and 0.05% in the composite, and 5.6 and 0.3% in the monolithic crystal, respectively. The relatively smaller load-free MFISs in the composite than the monolithic crystal resulted from the clamping of martensitic twin-boundary motion in the Ni-Mn-Ga plate by the PVDF films. The largest ME coefficient (α(E)) was 0.58 V/cm·Oe at a magnetic bias field (H(Bias)) of 8.35 kOe under load-free condition. The mechanism of the ME effect originated from the mechanically mediated MFIS effect in the Ni-Mn-Ga plate and piezoelectric effect in the PVDF films. The measured α(E)-H(Bias) responses under different loads showed good agreement with the model prediction.     

Intrinsic two-way shape memory effect in a Ni-Mn-Sn metamagnetic shape memory microwire

An intrinsic two-way shape memory effect with a fully recoverable strain of 1.0% was achieved in an as-prepared Ni_(50)Mn_(37.5)Sn_(12.5) metamagnetic shape memory microwire fabricated by Taylor-Ulitovsky method. This two-way shape memory effect is mainly owing to the internal stress caused by the retained martensite in austenite matrix, as revealed by transmission electron microscopy observations and highenergy X-ray diffraction experiments. After superelastic training for 30 loading/unloading cycles at room temperature, the amount of retained martensite increased and the recoverable strain of two-way shape memory effect increased significantly to 2.2%. Furthermore, a giant recoverable strain of 11.2% was attained under a bias stress of 300 MPa in the trained microwire. These properties confer this microwire great potential for micro-actuation applications.     

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.     

Ni–Mn–Ga shape memory alloys development in China

Study on Ni–Mn–Ga ferromagnetic shape memory alloys recently keeps active. Intermartensitic transformation was found. Magnetic field enhanced phase transformation strain was discovered, and achieved up to 4%. Fifteen percent super high strain induced by variant reorientation under stress was obtained in non-modulated martensite. Six percent large magnetic field induced strain was achieved, and the temperature dependence was investigated in 5-layered martensite single-variant Ni–Mn–Ga alloys. Several other systems of magnetic shape memory alloys and high temperature shape memory alloy Ni–Mn–Ga are also reviewed.     

形状记忆聚氨酯热力耦合变形行为实验和有限元模拟

在室温下对形状记忆聚氨酯进行不同应变率下的单调拉伸实验,结合红外测温仪对试样表面温度进行同步监测,研究拉伸过程中的热力耦合效应。结果表明:当应力达到屈服峰后,分子链解缠导致了屈服软化,同时分子链之间的摩擦诱发了局部化温升;随着载荷继续增加,分子链在拉伸方向优先取向导致应变硬化发生,响应的应力和温度不断升高。同时发现,屈服峰和局部化温升均随着应变率的增加而显著增加,然而材料耗散生热诱导的应变软化和应变硬化之间存在竞争机制,使得局部化塑性流动过程对应变率的敏感性降低。基于有限元软件ABAQUS建立板状试样拉伸的有限元模型,对形状记忆聚氨酯的拉伸变形进行热力耦合分析。通过比较不同时刻的塑性应变场和温度场云图发现,局部化的塑性流动和温升均从初始缺陷处萌生,并逐渐向中间移动直至扩展到整个试样。进而提取不同加载速率下的平均温升曲线与实验结果进行了对比,发现二者吻合度较高。     

预变形和热循环对Ni50Ti45Ta5形状记忆合金相变行为的影响

利用示差扫描量热仪研究了预变形和热循环对Ni54Ti45Ta5形状记忆合金相变行为的影响。研究结果表明：预变形后合金的马氏体发生了稳定化现象。形变后第一次热循环．逆相变温度增加。正相变温度降低；而第二次相变循环。马氏体的稳定化现象消失。热循环使相变温度降低。减少了相变热。     

Effect of Small γ Precipitates on the Two-way Shape Memory Effect in a Cu–Zn–Al Alloy

After the treatment for the Stabilization of Stress-Induced Martensite (SSIM) in Cu–Zn–Al alloys, it was found that the small γ precipitates in the β austenite are ellipsoidal with a large strain field oriented in the same direction, while in the martensite, the γ precipitates changed their shape from ellipsoidal to spheroidal, which relaxed the strain field. To check whether the strain field of the γ precipitates is available to produce thermoelastic martensitic transformation, in situ observations with a heating sample holder in TME were performed. It was found that after heating above the A_s temperature, the spherical γ precipitates in the martensite recovered their strain field and elliptical shape. During cooling, the strain field of the γ precipitates disappeared again. This means that the strain fields of the γ precipitates trained by the SSIM method play an important part in the thermoelastic martensitic transformation that presents the two-way shape memory effect.