哈斯勒合金Ni-Fe-Mn-In的马氏体相变与磁特性研究

利用电弧炉制备了Ni_50-xFe_xMn₃₇In₁₃(x=1, 3, 5) 多晶样品, 通过结构和磁性测量, 系统分析了Ni_50-xFe_xMn₃₇In₁₃(x=1, 3, 5)样品的晶体结构和马氏体相变. 结果表明, 三样品在室温下呈现出了不同的晶体结构. 同时, 随着Fe含量的增加, 样品的马氏体相变温度急剧下降, 而铁磁性却逐渐增强. 研究了Fe3和Fe5样品在反马氏体相变过程中的磁电阻和磁卡效应. 在外加3 T的磁场下, 两样品在反马氏体相变区域所表现出的磁电阻效应分别约为-46%和-15%, 而等温熵变则约为6 J·kg^{-1·K-1和9.5 J}·kg^{-1·K-1. 然而, 伴随非常宽的相变温跨和较小的磁滞损失, Fe3样品在反马氏体相变区域的净制冷量达到96 J}·kg^-1.     

Martensitic transformation in Cu-doped NiMnGa magnetic shape memory alloys

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 Ni_50-xCu_xMn₃₁Ga₁₉ (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 (k_F) is applied to evaluate the change of the martensitic transformation temperature. The increase of k_F leads to the increase of the martensitic transformation temperature.     

Martensitic transformation temperature hysteresis narrowing and magnetocaloric effect in ferromagnetic shape memory alloys Ni-Mn-Ga

The hysteresis narrowing and magnetocaloric effect (MCE) were studied in the Ni-Mn-Ga alloys. Ni₅₄Mn₂₄Ga₂₂ and Ni_51.9Mn₂₇Ga_21.1 were selected in order to obtain specific characteristic temperatures of alloys and to study an influence of several factors on the hysteresis width (δ) of basic austenite-martensite (AM) transformation. The effect of martensite crystal lattice softening due to intermartensitic transition (IT) taking place immediately after AM transformation on δ was examined in alloy 1. MCE was measured in alloy 2, in which Curie temperature (T_C) and austenitic start temperature (A_S) coincides. It was demonstrated that the hysteresis width δ reaches about 2 K, if IT is enough close to AM transition. MCE was found to have a maximum at T_C≈A_S.     

Intermartensitic transformation and magnetic field effect in NiMnInSb ferromagnetic shape memory alloys

Partially substituting Sb for In, we found an irreversible transformation of martensite to intermartensite at 90 K in Ni₅₀Mn₃₄In₁₂Sb₄ alloy during heating. The reverse transformation of martensite and intermartensite to the parent phase induced by a magnetic field has been investigated. The results indicate that, if a sufficiently high magnetic field is applied, the intermartensite state is no longer necessary as an intermediate state. Thus, a difference of the transformation originating from magnetic and from thermal energies has been found. In this competition, lattice distortions play an important role to promote the occurrence of the intermediate intermartensitic path.     

Martensitic phase transition with magnetocaloric effect and double-shifted exchange bias in the martensitic phase for Ni48Mn39Sn13-xGex alloys

Ni₄₈Mn₃₉Sn_13-xGe_x (x?=?1, 2) Heusler alloys have been prepared, and the martensitic phase transition (MPT), magnetocaloric effect and exchange bias (EB) have been explored. At room temperature, the structure of both samples presents L2₁ type, and the MPT shifts to a higher temperature, while the Curie temperature (T_C) of the austenitic phase decreases with the increase of the Ge content. The maximum magnetic entropy change of Ni₄₈Mn₃₉Sn_13-xGe_x with x?=?2 reaches about 14.67?J/kg?K under the magnetic field of 5?T during reverse MPT. In addition, an interesting phenomenon is the enhancement of EB with the increase of the Ge content, especially the abnormal presence of the double-shifted hysteresis loop has been realized in Ni₄₈Mn₃₉Sn_13-xGe_x with x?=?2, which can be interpreted by the fact that the antiferromagnetic (AFM) regions couple with proximal ferromagnetic (FM) regions in the opposite way at low temperature.     

Martensitic transformation and magnetic properties of ferromagnetic shape memory Fe66Pd30Rh4 alloys

This study mainly shows that in the Fe₆₆Pd₃₀Rh₄ (at%) alloys, the L1₀ phase plays an important role in magnetostriction due to the interplay of L1₀ martensitic twins with magnetic domains. The L1₀ martensitic twin structure exhibits a strong magnetocrystalline anisotropy energy constant (K_u=1.27-2.84×10⁶ (ergs/cm³)) along the tetragonal c axis direction. In addition, the L1₀ tetragonal martensitic twin structure shows both a perfect shape memory and a reversible shape memory effect; therefore, it is expected to be applicable in magneto-mechanical applications (such as microactuators or springs). However, in this study, we discover that solution treatment (ST) and aging heat treatments of Fe₆₆Pd₃₀Rh₄ ferromagnetic shape memory alloys influence the behavior of the martensitic transition, which is associated with the change in magnetic properties. The process of a thermoelastic L1₀+L1_m twin phase decomposition→non-thermoelastic L1₀+L1_m+α_bct structure in Fe₆₆Pd₃₀Rh₄ alloys during solution treatment and aging at 400-550 °C for various times is studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The relation of phase separation morphology to the magnetic property change is examined with a superconducting quantum interference device (SQUID) magnetometer, and magnetostriction measurement is performed with a strain gage method and magnetostrictive meter setup. The results indicate that the process of martensitic transformation during aging leads to an increase in coercivity and a decrease in magnetostriction, simultaneously.     

Pressure effects on magnetic properties and martensitic transformation of Ni–Mn–Sn magnetic shape memory alloys

The mechanism for the effects of pressure on the magnetic properties and the martensitic transformation of Ni-Mn- Sn shape memory alloys is revealed by first-principles calculations. It is found that the total energy difference between paramagnetic and ferromagnetic austenite states plays an important role in the magnetic transition of Ni-Mn-Sn under pressure. The pressure increases the relative stability of the martensite with respect to the anstenite, leading to an increase of the martensitic transformation temperature. Moreover, the effects of pressure on the magnetic properties and the martensitic transformation are discussed based on the electronic structure.     

Ni-Fe-Ga磁致形状记忆合金中间马氏体相变

采用差示扫描量热和x射线衍射技术研究Ni-Fe-Ga磁致形状记忆合金的马氏体相变行为.结 果发现,在多晶Ni565_56.5Fe190_19.0Ga245_{2 4.5}和Ni563_56.3Fe170_17.0 Ga267_26.7合金中除马氏体相变外,还观察到一次完整的、正相变和逆相 变对应出现、单 纯由温度诱发的中间马氏体相变.该中间马氏体相变与马氏体相变均为热弹性相变. 关键词： Ni-Fe-Ga 中间马氏体相变 磁致形状记忆合金     

Martensitic transformation of TiNiPd high-temperature shape memory alloys: A first-principles study

Heat of formation, elastic property and electronic structure of TiNiPd high-temperature shape memory alloys have been investigated by first-principles calculations using the pseudopotentials plane-wave method. The results show that the heat of formation difference between austenite and martensite plays an important role in the martensitic transformation. The effect of Pd content on the martensitic transformation temperature and transformation type is clarified based on the elastic constants of the B2 phases. High martensitic transformation temperature can be attributed to a low shear resistance C′. Furthermore, the mechanism of the effect of Pd addition on elastic constants is explained on the basis of the electronic structure.     

哈斯勒合金Ni-Co-Mn-Sn的马氏体相变及其磁热效应研究

通过结构和磁性测量,研究了四元哈斯勒合金Ni_50-xCo_xMn₃₈Sn₁₂（x=1, 2, 4, 6, 8）的晶体结构和相变特征.结果表明,Co原子的掺杂不但没有影响三元哈斯勒合金Ni-Mn-Sn的原有结构,而且还增强了样品在奥氏体相的铁磁交换作用.此外,通过Maxwell方程计算了其中三种成分样品（x= 2, 4, 6）的磁熵变ΔS_{M关键词： 哈斯勒合金 Ni-Co-Mn-Sn 马氏体相变 磁热效应}     

Magnetic properties and large magnetocaloric effects in amorphous Gd-Al-Fe alloys for magnetic refrigeration

A series of the amorphous Gd75-55Al25-5Fe0-40 alloy ribbons were prepared by melt spinning.The structure,magnetic properties and magnetocaloric effect(MCE) of these alloys were investigated.The prepared samples have shown the characteristics of a second-order phase transition with zero hysteresis loss and the Tc can be tuned by changing the Fe contents.For the different compositions,the magnetic entropy change(--Sm) for a field change of 0-5 T reached a maximum value of 7.14 J kg-1 K-1 in the Gd70Al20Fe10 a...     

铁磁形状记忆合金Ni52.2Mn23.8Ga24的马氏体相变及其物理表征

对Ni52.2Mn23.8Ga24的单晶样品在马氏体相变过程中的相变潜热、磁性、电阻以及应变等物理序参量进行了测量.测量结果表明:不同的物理机制表征的相变温度有所不同.利用马氏体相变的GT关系予以分析,解释了不同测量方法获得的相变温度差别的原因.研究指出,Heusler合金Ni2MnGa的相变是分布晶格畸变类型,磁结构的变化发生在第二步晶格的非均匀切变,但相变应变与GT模型有区别. 关键词： 马氏体相变 Ni52.2Mn23.8Ga24     

A magnetic Compton scattering study of Ga rich Co-Ni-Ga ferromagnetic shape memory alloys

The temperature dependent spin momentum densities of Co(1.8)NiGa(1.2) and Co(2)Ni(0.76)Ga(1.24) alloys have been measured using the magnetic Compton scattering technique. The individual contributions of constituents in the formation of the total spin moment are also calculated using Compton line shape analysis. The magnetic Compton data when compared with the magnetization data obtained using a vibrating sample magnetometer show a negligible orbital contribution. The spin moments deduced from the experimental Compton data are compared with the theoretical results obtained from the full potential linearized augmented plane wave method and are found to be in good agreement. The origin of the magnetism in both alloys is also described in terms of the e(g) and t(2g) contributions of Ni and Co.     

Quantitative model of large magnetostrain effect in ferromagnetic shapell memory alloys

A quantitative model describing the large magnetostrain effect observed in several ferromagnetic shape memory alloys such as Ni₂MnGa is briefly reported.The paper contains an exact thermodynamic consideration of the mechanical and magnetic properties of similar types of materials. As a result, the basic mechanical state equation including magnetic field effect is directly derived from a general Maxwell relation. It is shown that the magnetic field induced deformation effect is directly connected with the strain dependence of magnetization. A simple model of magnetization and its dependence on the strain is considered and applied to explain the results of experimental study of large magnetostrain effects in Ni₂MnGa. Received 29 September 1999     

Influence of Ni/Mn ratio on magnetostructural transformation and magnetocaloric effect in Ni_(48-x)Co_2Mn_(38+x)Sn_(12)(x = 0, 1.0, 1.5, 2.0,and 2.5) ferromagnetic shape memory alloys

An investigation on the magnetostructural transformation and magnetocaloric properties of Ni_(48-x)Co_2Mn_(38+x)Sn_(12)(x = 0, 1.0, 1.5, 2.0, and 2.5) ferromagnetic shape memory alloys is carried out. With the partial replacement of Ni by Mn in the Ni_(48)Co_2Mn_(38)Sn_(12) alloy, the electron concentration decreases. As a result, the martensitic transformation temperature is decreased into the temperature window between the Curie-temperatures of austenite and martensite. Thus, the samples with x = 1.5 and 2.0 exhibit the magnetostructural transformation between the weak-magnetization martensite and ferromagnetic austenite at room temperature. The structural transformation can be induced not only by the temperature,but also by the magnetic field. Accompanied by the magnetic-field-induced magnetostructural transformation, a considerable magnetocaloric effect is observed. With the increase of x, the maximum entropy change decreases, but the effective magnetic cooling capacity increases.     

Laser beam interaction with Ni-Mn-Ga ferromagnetic shape memory alloys

Laser beam interaction with alloys belonging to the Ni-Mn-Ga ferromagnetic shape memory alloy group has been investigated in order to assess the possibilities to use laser radiation for processing these materials, as for machining, joining or surface modification. The brittleness of Ni-Mn-Ga alloys is, as expected, an important factor and the formation of cracks appears to be difficult to be avoided. The laser interaction leads to vaporization on the impact zone and the changes in the chemical composition have been analyzed with respect to the beam parameters for penetration and surface melting, respectively.     

Micromemory effects in shape memory alloys

Summary Thermoelastic martensitic transformations (TMT) have been on the stage for several years in connection with shape memory alloys. Interest has recently grown in partial cycling or involving the incomplete reverse transformation in a pre-programmable way. Attention is here focussed on the hysteresis cycle of several TMT (NiTi, NiTiFe, AgCd) related either to a complete transformation or to incomplete cycling as required to activate stimulated stepwise martensite-to-austenite reversible transformation (SMART). The modifications of the hysteresis cycles are discussed in the light both of built-in kinetics barriers and of the hierarchy of symmetries between parent and product phase. In honour of Prof. Fausto Fumi on the occasion of his retirement from teaching.     

Martensitic transformation in Ni-Mn-Ga alloys

Single crystals of different compositions in shape memory alloys Ni-Mn-Ga have been studied by electron and low temperature X-ray diffraction as well as by differential scanning calorimetry. It is shown that the cooling-induced martensitic phases are long-periodic ones modulated along the (110) directions by a transverse wave of atomic shifts with 5 and 7 atomic layers periodicity for the alloys studied exhibiting a martensitic transformation at 180 K and 446 K, respectively. The transformation heats appeared to be about 10 times different for both alloys.