共查询到19条相似文献,搜索用时 328 毫秒
1.
对具有两步完全热弹性的Ni53.2Mn22.6Ga24.2单晶的物性采用多种测量手段进行了表征,特别研究了不同温度下的应力-应变特性.研究表明,热诱发的中间马氏体相变应变远大于马氏体相变应变.在较低的形变温度下,沿单晶母相[001]方向的压应力诱发的是两步马氏体相变,材料表现出赝弹性;在较高的形变温度下,只能观察到一步马氏体相变,材料展现出完全超弹性特性.此外,利用热力学理论分别计算了诱发马氏体相变和中间马氏体相变的临界应力与形变温度的关系,与实验测量得到的结果相符.
关键词:
马氏体相变
形状记忆效应
应变
超弹性 相似文献
2.
用真空快淬炉制备了名义成分为Ni50Mn27Ga23,淬速 分别为2,4,8m/s的快淬态试样,并将部分试样热处理.研究结果表明,与铸态相比,快淬态试样马氏体相 变温度、居里温度均有所降低,经热处理后,降低的马氏体温度和居里温度会提高.快淬合 金与铸态合金相比更容易获得单相的Ni2MnGa结构,并能使合金主衍射峰从(22 0)转向( 400),形成织构,热处理后织构消失.快淬工艺对相变应变和磁致应变的影响表现出复杂性 ,研究发现获得织构的快淬带具有较浇铸态试样更大的相变应变和磁致应变.
关键词:
50Mn27Ga23')" href="#">Ni50Mn27Ga23
快淬
马氏体相变
应变 相似文献
3.
测量了Ni52Mn24Ga24单晶样品在磁场加载和未加载情 况下马氏体相变时的相变应变.分析结果表明:用提拉法生长单晶时在晶体内部引入了单一取向的内应力,该取向内应力可诱导马氏体变体择优取向,从而导致马氏体相变时产生大的相变应变.从理论上计算了该内应力的大小.另外,对样品在马氏体态单纯磁诱导应变的热动力学研究,表明取向内应力在马氏体态依然存在.
关键词:
马氏体相变
磁感生应变
内应力 相似文献
4.
5.
研究了预先热磁处理对Ni503Mn287Ga21单晶的磁学和力学性能的影响.首先将样品加热到居里温度之上让其冷却,冷却方式分为两种:一种是施加一定大小的磁场从高于居里温度冷却至室温,另一种是在样品经历顺磁-铁磁相变后但还未发生奥氏体-马氏体相变前施加相同大小和方向的磁场并冷却至室温.室温时的拉伸-压缩实验结果表明单晶样品在经历前一种处理后,其可逆应变、磁化强度的变化 (ΔM)比后一种处理的相应值要小很多.在后一种热磁处理的样品中,顺磁-铁磁相变发生后形成了自发磁畴,但这种磁畴不具有择优取向.在顺磁-铁磁相变结束后施加磁场,容易导致择优的马氏体准单畴出现,从而表现出大的可逆应变和ΔM.但对于前者,我们认为样品从居里温度降到室温过程中,其中的磁畴在相同的磁场作用下获得择优生长,形成大磁畴,导致磁诱导的强各向异性.这种择优取向的大磁畴在随后马氏体相变期间影响着马氏体的自发排列方式,不利于马氏体准单畴的出现,结果导致较小的可逆应变和ΔM.
关键词:
磁和力学锻炼
Ni-Mn-Ga单晶
铁磁和马氏体相变 相似文献
6.
7.
利用电弧炉熔炼了Ni50Mn35In15多晶样品,根据磁性测量对其马氏体相变和磁热效应进行了系统研究.结果表明,随着温度的降低,样品在室温附近先后发生了二级磁相变与一级结构相变特征的马氏体相变,导致它的磁化强度产生突变. 同时通过低温下的磁滞回线的测量发现样品存在交换偏置行为,表明低温下马氏体相中铁磁和反铁磁共存. 此外,根据Maxwell方程,计算了样品在马氏体相变温度附近的磁熵变,当温度为309K,磁场改变5 T时,样品的磁熵变可达22.3J/kgK.
关键词:
哈斯勒合金
50Mn35In15')" href="#">Ni50Mn35In15
马氏体相变
磁热效应 相似文献
8.
通过往母合金Ni51.5Mn25Ga23.5掺入7种IVA, VA和VIA 过渡族元素得到系列掺杂合金Ni51.5Mn23M2Ga23 .5.M为掺杂元素.实验结果表明,掺杂效应一般引起马氏体相变温度的下降,其中,W 的掺杂是7种元素中唯一使相变温度升高的特例,且出现了中间马氏体相变.同时,在价电子 浓度不变的情况下,相变更敏感于原子的尺度效应.实验发现,Ti,Zr,Hf,V四种非磁性元 素的掺杂使Mn原子磁矩减小,而Nb,Ta,W三种非磁性元素的掺杂却可以明显地增大Mn原子 的磁矩.在考察掺杂效应时,不能忽略马氏体相变引起的晶格变化对材料磁性的影响.
关键词:
NiMnGa
掺杂
马氏体相变
磁性 相似文献
9.
成功生长了Co50Ni21Ga29:Si(x=1,2)单晶样品,对其磁性,马氏体相变及其相关性质进行了细致的测量.发现掺Si成分的单晶具有非常迅速的马氏体相变行为、2.5%的大相变应变、大于100 ppm的磁感生应变和4.5%的相变电阻.进一步研究指出,在CoNiGa合金中掺入适量Si元素,能够降低材料的马氏体相变温度,减小相变热滞后,提高材料的居里温度,并使得磁性原子的磁矩有所降低.尤其重要的是Si元素的添加能够增大材料马氏体的磁晶各向异性能,改善马氏体变体的迁移特性,从而获得更大的磁感生应变.
关键词:
铁磁形状记忆合金
Heusler合金
50Ni21Ga29Six')" href="#">Co50Ni21Ga29Six 相似文献
10.
11.
用熔炼和甩带的方法制备了组分为Ni50FexMn25-xGa 25(x=0—25) 的系列样品.x射线衍射实验结果表明,当Fe取代Mn的含量x<17时,用熔炼和甩带的方法均 能合成高度有序的L21结构的Heusler相.而当x>17时,普通熔炼方法只能得到 低有序度的 γ相,只有采用甩带急冷的方法才能获得高度有序的纯L21结构的化合物.根据 交流磁化率 和分子磁矩的测试结果,初步分析了Fe原子对化合物磁性的贡献,认为Fe原子占据了Mn原子 的位置后,具有高于一般含铁合金的原子磁矩,可达2.55—3.55μB.
关键词:
Heusler合金
50FexMn25-xGa25 sub>')" href="#">Ni50FexMn25-xGa25 sub> 相似文献
12.
The Ni2 + x
Mn1 − x
Ga magnetic shape memory alloys at concentrations x = 0.18–0.36 have been studied using small-angle polarized neutron scattering in magnetic fields 0 < H ≤ 5.7 kOe. In this concentration range, the alloy undergoes a coupled magnetic-structural phase transition. At x < 0.18, the martensitic phase transition occurs, as usual, in the ferromagnetic state, i.e., T
m
< T
C (T
m
and T
C are the temperatures of the martensitic and magnetic phase transitions, respectively). However, at x > 0.27, the relationship between the characteristic temperatures is changed, i.e., T
m
> T
C. The small-angle polarized neutron scattering data indicate that, in the concentration range under investigation, there occurs
a complex transformation of the magnetic and atomic structures. All phase transitions exhibit a temperature hysteresis of
scattering and polarization, which is characteristic of first-order phase transitions. A comparative analysis of the mesoscopic
structures of the Ni2 + x
Mn1 − x
Ga and Ni2 + x + y
Mn1 − x
Ga1 − y
alloys studied using the small-angle polarized neutron scattering technique has been carried out. 相似文献
13.
Igor Dubenko Mahmud Khan Arjun Kumar Pathak Bhoj Raj Gautam Shane Stadler Naushad Ali 《Journal of magnetism and magnetic materials》2009,321(7):754-757
The Mn-based Heusler alloys encompass a rich collection of useful materials from highly spin-polarized systems to shape memory alloys to magnetocaloric materials. In this work we have summarized our studies of magnetostructural transitions from paramagnetic austenite to ferromagnetic martesite phases at TMC in Ni2MnGa-based alloys (Ni2Mn0.75Cu0.25-xCoxGa, Ni2Mn0.70Cu0.30Ga0.95Ge0.05, Ni2Mn1-xCuxGa, Ni2+xMn1-xGa, and Ni2Mn0.75-xCuxGa), and martensitic transitions from the ferromagnetic austenite to the martesite state in off-stoichiometric Ni-Mn-(In/Sb) Heusler alloys. The phase transition temperatures and respective magnetic entropy changes (ΔS) depend on composition in these systems and have been determined from magnetization measurements in the temperature interval 5-400 K, and in magnetic fields up to 5 T. It is shown that, depending on the composition and doping scheme the “giant” ΔS=40-60 J/(kgK) (for a field change of 5 T) can be observed in the temperature range (300-360 K) for the Ga-based alloys. The interplay between or coupling of the various transitions in Ni2Mn(Mn,X) systems with X=Sb and In leads to exchange bias effects, giant magnetoresistance, and both inverse and “normal” magnetocaloric effects. 相似文献
14.
The effect of Si content on the martensitic transfor-mation temperature of Ni55.5e18Ga26.5-xSix alloys 下载免费PDF全文
This paper investigates the effects of substitution of Si for Ga on the martensitic transformation behaviours in Ni-Fe-Ga alloys by using optical metallographic microscope and differential scanning calorimetry (DSC) methods. The structure type of Ni55.5Fe18Ga26.5-xSix alloys is determined by x-ray diffraction (XRD), and the XRD patterns show the microstructure of Ni-Fe-Ga-Si alloys transformed from body-centred tetragonal martensite (with Si content x = 0) to body-centred cubic austenite (with x = 2) at room temperature. The martensitic transformation temperatures of the Ni55.5Fe18Ga26.5-xSix alloys decrease almost linearly with increasing Si content in the Si content range of x ≤ 3. Thermal treatment also plays an important role on martensitic transformation temperatures in the Ni-Fe-Ga-Si alloy. The valence electronic concentrations, size factor, L21 degree of order and strength of parent phase influence the martensitic transformation temperatures of the Ni-Fe-Ga-Si alloys. An understanding of the relationship between martensitic transformation temperatures and Si content will be significant for designing an appropriate Ni-Fe-Ga-Si alloy for a specific application at a given temperature. 相似文献
15.
Effects of Ga substitution for Sn on the structure and magnetic properties of TbMn6Sn6-xGax (x=0.0-1.2) compounds have been investigated by means of x-ray diffraction, magnetization measurement and 119Sn M?ssbauer spectroscopy. The substitution of Ga for Sn results in a decrease in lattice constants and unit-cell volumes. The magnetic ordering temperature decreases monotonically with increasing Ga content from 423 K for x=0.0 to 390 K for x=1.2. At room temperature, the easy magnetization direction changes from the c-axis to the ab-plane. This variation implies that the substitution of Ga for Sn leads to a decrease in the c-axis anisotropy of the Tb sublattice. An increase in the non-magnetic Ga concentration results in a monotonic decrease of the spontaneous magnetization Ms at room temperature. Since there are three non-equivalent Sn sites, 2c (0.33, 0.67,0), 2d (0.33, 0.67,0.5) and 2e (0,0,0.34) in the TbMn6Sn6-xGax compounds, the 119Sn M?ssbauer spectra of the TbMn6Sn6 and TbMn6Sn5.4Ga0.6 compounds can be fitted by three sextets. The hyperfine fields (HFs) decrease in the order of HF(2d)>HF(2e)>HF(2c), which is in agreement with the magnetic structure. 相似文献
16.
通过X射线衍射及磁测量手段研究了Er2AlFe16-xMnx(x=1,2,3,4,6,8)化合物的结构和磁性. 研究结果表明Er2AlFe16-xMnx化合物具有六角相的Th2Ni17型结构. 采用X射线热膨胀测定法在103—654K的温度范围内测量了Er2AlFe16-xMnx(x=1,2,3,4)化合物的热膨胀性质,发现这些化合物在低温下存在热膨胀反常现象,在居里点附近具有负膨胀性质. 对自发磁致伸缩的研究结果表明Er2AlFe16-xMnx化合物中存在着较强的各向异性的自发磁致伸缩,低温下自旋重取向的出现使得化合物的自发体磁致伸缩有所增强. 磁测量结果表明Mn的替代导致Er2AlFe16-xMnx化合物的居里温度及自发磁化强度急剧下降,并且使得化合物的磁晶各向异性发生显著改变.
关键词:
2AlFe16-xMnx化合物')" href="#">Er2AlFe16-xMnx化合物
反常热膨胀
自发磁致伸缩 相似文献
17.
通过X射线衍射及磁测量手段研究了Dy2AlFe16-xMnx化 合物的结构和磁性.研究结果表明Dy2AlFe16-xMnx化合 物具有六角相的Th2Ni17型结构.对x=1,2的样品采用X射线热膨胀 测定法在104—647K的温度范围内测量了其热膨胀性质,发现这些化合物在低温下存在热膨 胀反常现象,在居里点附近出现负膨胀性质.对自发磁致伸缩的研究结果表明Dy2AlFe16-xMnx化合物中存在着较强的各向异性的自发磁致伸缩,随 着Mn含量的增加,其低温下的自发体磁致伸缩减弱.磁测量结果表明Mn的替代导致Dy2< /sub>AlFe16-xMnx化合物的居里温度及自发磁化强度急剧下降.
关键词:
2AlFe16-xMnx化合物')" href="#">Dy2AlFe16-xMnx化合物
反常热膨胀
自发磁致伸缩
自发磁化强度 相似文献
18.
This paper studies the martensitic transformation in the Cu-doped NiMnGa alloys. The orthorhombic martensite transforms to L21 cubic austenite by Cu substituting for Ni in the Ni50-xCuxMn31Ga19 (x=2--10) alloys, the martensitic transformation temperature decreases significantly with the rate of 40 K per Cu atom addition. The variation of the Fermi sphere radius (kF) is applied to evaluate the change of the martensitic transformation temperature. The increase of kF leads to the increase of the martensitic transformation temperature. 相似文献
19.
Bhoj Raj Gautam Igor Dubenko Arjun Kumar Pathak Shane Stadler Naushad Ali 《Journal of magnetism and magnetic materials》2009,321(1):29-33
The influence of the substitution of manganese by boron on the crystal structure and magnetic properties of Ni2Mn1−xBxGa Heusler alloys with 0?x?0.5 has been investigated using X-ray diffraction, thermal expansion, resistivity, and magnetization measurements. The samples with concentrations x<0.25 were found to be of single phase and belonged to the cubic L21 crystal structure at room temperature. Crystal cell parameters of the alloys decreased from 5.830 to 5.825 Å with increasing boron concentration (x) from 0 to 0.25. The alloys were ferromagnetically ordered at 5 K and the saturation magnetization decreased with increasing boron concentration. The ferromagnetic ordering and structural transition temperatures for 0?x?0.3 have been observed and the phase (x−T) diagram of the Ni2Mn1−xBxGa system was constructed. The phase (x−T) diagram indicates that the ground state of Ni2Mn1−xBxGa alloys belongs to ferromagnetic martensitic, premartensitic, and austenitic phases in x?0.12, 0.12<x?0.18, and 0.18<x?0.3, respectively. The relative influence of cell parameters and electron concentrations on the phase diagram is discussed. 相似文献