The influence of microstructure on the martensitic transformation in Cu–Zn–Al melt-spun ribbons

The martensitic transformation was investigated in a set of twin roller melt-spun Cu–Zn–Al shape memory alloys, solidified at tangential wheel speeds between 20 and 40 m/s. The resulting microstructures were analyzed using X-ray diffraction, optical and transmission electron microscopy techniques. The characteristic martensitic transformation temperature, M _S, was determined for each condition by conventional resistometric methods. The ribbons are homogeneous in shape and for each quenching rate they exhibit a quite uniform M _S temperature. By proper thermal treatments, the different factors affecting M _S could be separately examined and from temperature measurements, the contribution of L2₁ antiphase boundaries evaluated. A calculation of this contribution using pair interchange energies is in good agreement with the experimental results.     

A 20-resolved hadox study of BaTiO3

The fine structure of YBaCu₃O₇ is examined: Twin organization, planar defects, and structural phase co-existence are discussed in the context of the tetragonal to orthorhombic transformation. Heterogeneous nucleation of an insulating phase at the twin boundary and sub-grain boundaries is demonstrated. On the basis of the morphological observations, the transformation is classified as martensitic. Considering the role of twin in relieving the martensitic transformation strain, by producing a low strain energy habit plane, the feasibility of the formation of a twinless structure is discussed.     

Characteristics of thermoelastic martensitic transformations in heterophase ferromagnetic Ni<Subscript>54</Subscript>Fe<Subscript>19</Subscript>Ga<Subscript>27</Subscript> single crystals

Using single-crystal Ni ₅₄ Fe ₁₉ Ga ₂₇ (at.%) specimens, the effects of heat treatment, annealing at the temperatures within T = 473–1473 K for one hour followed by quenching into water, on the development of thermoelastic L2₁-L1₀ martensitic transformations is investigated. It is found out that using proper heat treatment modes one can control the temperature of L2₁-L1₀ martensitic transformations, the value of the temperature hysteresis, the critical stresses of twin boundary motion, and certain functional properties of single-crystal Ni-Fe-Ga. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 24–27, October, 2007.     

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.     

Magnetic and structural properties of non-stoichiometric Ni-Mn-Ga ferromagnetic shape memory alloys

Structural and magnetic transition temperatures of ferromagnetic shape memory alloys present a strong dependence on slight departures from the stoichiometry, as does the mobility of twin boundaries responsible for the large magnetic field induced strains. In this work we study four non stoichiometric Ni-Mn-Ga polycrystalline alloys with compositions of 43–52 at.% nickel, excess manganese and deficient in gallium, and a single crystal of composition Ni₅₂Mn₂₆Ga₂₂. Those compounds are of technical interest due to the observed large room temperature magnetic field induced strains. Calorimetric and magnetic measurements determined the martensitic transition and Curie temperatures of the alloys (A_S = 331 K and T_Curie = 366 K for 52 at.% nickel alloy). Nickel defective alloys present a martensitic transition region broader than excess nickel ones. Neutron powder diffraction analysis confirmed orthorhombic martensitic structures for nickel defective alloys, and tetragonal for excess nickel ones. In the 52 atomic % nickel alloys case the crystallographic structure of the martensitic phase was also obtained on a single crystal with the same composition, trained to get a single variant in agreement with determined in the powder sample.     

哈斯勒合金Ni-Mn-Ga的马氏体相变和磁增强双向形状记忆效应

通过研究铁磁性金属间化合物Ni_2+xMn_1-xGa(x=-0.1,0,0.08,0.13,0.18,0.2)和Ni_2-xMn_1+x/2Ga_1+x/2(x=-0.1,0,0.04,0.06,0.1)两个系列多晶样品的交流磁化率随温度的变化行为,得到了化合物在不同组分下的马氏体相变温度TM和居里温度T_C.发现随着Ni成分的增加,前者的马氏体相变温度T_m增加,而居里温度T_C降低,后者的马氏体相变温度T_m和居里温度T_C均是先增大后减小.报道了T_m在室温附近的单晶样品Ni₅₂Mn₂₄Ga₂₄的磁场增强双向形状记忆效应.发现伴随着马氏体相变,样品在[001]方向可产生1.2%的收缩.如果在该方向施加1.2T的偏磁场可以使该应变值增大到4.0%.而垂直于[001]方向施加1.2T的偏磁场时,在[001]方向产生1.6%的膨胀.阐明了产生大应变的原因并非相界移动,而是单晶的杂散内应力小和外加磁场通过孪晶界移动使马氏体变体重组的共同结果. 关键词： 形状记忆效应 马氏体相变 2MnGa')" href="#">Ni₂MnGa     

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.     

Orientations of type II twin boundaries in B2→B19′ martensitic transformation in dynamic theory

The paper analyzes the possibility of describing the orientations of type II twin boundaries in B2→B19′ martensitic transformation in the framework of dynamic theory based on the concepts of heterogeneous nucleation and wave growth of martensite crystals. It is shown that the twin boundary orientations can be defined by strain fields in crystal contact regions characteristic of self-accommodated groups with common 〈001〉_B2 poles.     

Formation of nanostructured states in ternary TiNiFe-based shape memory alloys during megaplastic deformation and subsequent heat treatment

The ternary metastable TiNiFe alloys that exhibit a low-temperature shape memory effect and are subjected to plastic deformation by rolling or high-pressure torsion followed by heat treatment are studied by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and electrical resistivity measurements. It is found that moderate plastic deformation of a Ti₅₀Ni₄₉Fe₁ alloy at room temperature initiates the thermoelastic B2 ? B19’ martensitic transformation and the formation of a developed banded dislocation and twin substructure in the B19’ martensite. This deformation of a Ti₅₀Ni₄₇Fe₃ alloy forms a similar dislocation substructure but in B2 austenite. Megaplastic deformation by high-pressure torsion causes amorphization in the Ti₅₀Ni₄₉Fe₁ alloy and nanofragmentation in the Ti₅₀Ni₄₇Fe₃ alloy. The evolution of the nanostructure and the martensitic transformations in TiNiFe-based ternary alloys is studied during plastic deformation and subsequent annealing at various temperatures.     

Formation of a martensitic twins structure in Ni<Subscript>2.16</Subscript>Mn<Subscript>0.84</Subscript>Ga heusler alloy by high magnetic fields under adiabatic and isothermal conditions

The results are presented from experimental studies of the formation of martensitic twin structures in Ni_2.16Mn_0.84Ga Heusler alloy under the effect of magnetic fields of up to 14 T using a specially developed optical microscope under isothermal and adiabatic conditions. A qualitative model is proposed that explains the differences between the progress magnetoinduced magnetostructural first-order phase transitions under different thermodynamic conditions.     

Effects of pre-deformation on the martensitic transformation and magnetocaloric property in Ni-Mn-Co-Sn ribbons

This paper investigates the martensitic transformation and magnetocaloric effect in pre-deformed Ni-Mn-Co-Sn ribbons.The experimental results show that the reverse martensitic transformation temperature T M increases with the increasing pre-pressure,suggesting that pre-deformation is another effective way to adjust T M in ferromagnetic shape memory alloys.Large magnetic entropy changes and refrigerant capacities are obtained in these ribbons as well.It also discusses the origin of the enhanced martensitic transformation temperature and magnetocaloric property in pre-deformed Ni-Mn-Co-Sn ribbons.     

Si掺杂的铁磁形状记忆合金Co50Ni21Ga29Six的物性研究

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 50Ni₂₁Ga₂₉Si_x')" href="#">Co₅₀Ni₂₁Ga₂₉Si_x     

哈斯勒合金Ni-Mn-Sn的马氏体相变与反磁热性质

通过结构以及磁性测量,研究了哈斯勒合金Ni₅₀Mn_25+xSn_25-x (x=11,12)的马氏体相变和磁热性质.结果表明,与样品在奥氏体相的磁性不同,由于在马氏体相中反铁磁交换作用的增强,导致铁磁和反铁磁在马氏体状态下共存.此外,通过Maxwell方程,研究了两样品在不同磁场变化下马氏体相变温度附近的反磁热性质,并阐明了该系列合金产生大的正磁熵变(ΔS_M)不仅与其在降温过程中发生马氏体相变所导致的磁跃变(ΔM)有关,而且与发生马氏体相变所经历的温度区间有密切的联系. 关键词： 哈斯勒合金 Ni-Mn-Sn 马氏体相变 正磁熵变     

The effect of Si content on the martensitic transfor-mation temperature of Ni55.5e18Ga26.5-xSix alloys

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 Ni_55.5Fe₁₈Ga_26.5-xSi_x 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 Ni_55.5Fe₁₈Ga_26.5-xSi_x 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.     

掺杂对Ni51.5Mn25Ga23.5相变行为和磁性的影响

通过往母合金Ni_51.5Mn₂₅Ga_23.5掺入7种IVA, VA和VIA 过渡族元素得到系列掺杂合金Ni_51.5Mn₂₃M₂Ga_{23 .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     

Magneto-optical spectroscopy of the martensitic transition in Fe48Mn24Ga28 Heusler alloys

Magneto-optical spectra of polycrystalline samples of the Fe₄₈Mn₂₄Ga₂₈ Heusler alloy undergoing martensitic transformation from the high-temperature paramagnetic austenitic to ferromagnetic martensitic phase have been studied at 50–320 K in the transversal Kerr effect geometry. A comparison of magnetooptical spectra with data obtained in magnetic measurements has demonstrated that the martensitic transition on the surface of a sample and in its bulk takes place in the same temperature interval. Magnetic anisotropy has been found in the martensitic phase driven by large multidomain inclusions of martensite in austenite. The magneto-optical signal of Fe₄₈Mn₂₄Ga₂₈ differs strongly in spectral shape from that measured in Ni-Mn-Ga.     

热磁预处理对Ni-Mn-Ga单晶磁学和力学性能的影响

研究了预先热磁处理对Ni_503Mn_287Ga₂₁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     

Effect of alloying on the structure and phase transformations in Ni-Mn alloys alloyed by titanium

The crystal structure of NiMn alloy alloyed by titanium in a wide range of temperatures and compositions has been investigated using resistivity measurements, transmission electron microscopy, electron diffraction, and X ray diffraction. It is found that alloying by titanium not only decreases the martensitic transformation temperature but also changes the martensite crystal structure. The martensitic transformation temperatures are determined and the diagram of martensitic transformations for Ni₅₀Mn_{50 ? x} Ti _x alloys is constructed.     

Phase transitions and thermal expansion in Ni<Subscript>51–<Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript>36 + <Emphasis Type="Italic">x</Emphasis></Subscript>Sn<Subscript>13</Subscript> alloys

Thermal expansion and structural and magnetic phase transitions in alloys of the Ni–Mn–Sn system have been investigated. The spontaneous martensitic transformation in Ni_51–xMn_{36 + x}Sn₁₃ (0 ≤ x ≤ 3) alloys is found to be accompanied by high jumps in the temperature dependences of the linear thermal expansion. The relative change in the linear sizes of these alloys at the martensitic transformation is ~1.5 × 10^–3. There are no anomalies in the magnetic-ordering temperature range in the temperature dependences of the coefficient of linear thermal expansion. The differences in the behavior of linear thermal expansion at the martensitic transformation in Ni_51–xMn_{36 + x}Sn₁₃ (0 ≤ x ≤ 3) and Ni₄₇Mn₄₀Sn₁₃(x = 4) alloys have been established.     

哈斯勒合金Ni50Mn35In15的马氏体相变及其磁热效应

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