Ni55Mn25Ga18Ti2高温形状记忆合金的热循环稳定性

选择双相韧化的Ni?Mn?Ga?Ti高温形状记忆合金为研究对象。制备了淬火态Ni₅₅Mn₂₅Ga₁₈Ti₂高温形状记忆合金,并对其在室温至480 ℃之间进行高达500次的相变热循环,获得了5, 10, 50, 100和500次热循环态样品。采用X射线衍射、扫描电镜、能谱仪、同步热分析仪及室温压缩等实验方法,研究了淬火态和热循环态合金样品的微观组织、相变行为、力学及记忆性能,进而分析其热循环稳定性。研究结果表明:经500次循环后,Ni₅₅Mn₂₅Ga₁₈Ti₂合金相结构和显微组织未发生明显变化,均为由非调制四方结构的板条马氏体相和面心立方富Ni的γ相组成的双相结构;随着循环次数增加,马氏体相变温度几乎不变,逆马氏体相变温度和相变滞后在循环5次后趋于稳定;抗压强度及压缩变形率波动幅度较小;形状记忆性能下降,但形状记忆应变仍保持在1.4%以上;Ni₅₅Mn₂₅Ga₁₈Ti₂高温形状记忆合金显示出良好的热循环稳定性。      

Martensitic Transformation and Magnetic-Field-Induced Strain in Ni-Mn-Ga-RE （RE = Tb, Sm） Alloys

The effects of microamount additions of RE (Tb, Sm) on martensitic transition, the magnetic-field-induced strain and the bending strength of highly textured polycrystal line Ni4sMn33Ga19 alloy were investigated. The experimental results show that the addition of RE elements decreases the martensitic transformation temperature and the Curie temperature. But the bending strength of Ni-Mn-Ga-RE (RE=Tb, Sm) alloys increases remarkably because of the grain refinement. As a result, Ni-Mn-Ga-RE alloys will be applied practically with higher reliability and stability due to favorable plasticity and toughness. In addition, the replacement of small amounts Ga by Tb or Sm decreases the magnetic-field-in-duced strain of the alloys at room temperature.     

Ni_(43)Mn_(46-x)T_xSn_(11)(T=Fe,Co,Ni)合金的马氏体相变和磁熵变

通过示差扫描量热仪和振动样品磁强计对Ni43Mn46-xTxSn11(T=Fe,Co,Ni)铁磁形状记忆合金的相变、磁性以及磁熵变进行了研究。结果表明,由于价电子浓度的增加,Fe,Co,Ni替代Mn使马氏体转变温度大幅提高。Fe,Ni掺杂对马氏体居里温度(TCM)影响不大,Co则使TCM略有下降;奥氏体居里温度(TCA)对成分比较敏感,Fe,Ni的加入均使TCA略有提高,而Co则会大大提高TCA。由于马氏体相变伴随着磁化强度的突变,Ni43Mn46-xTxSn11合金在马氏体相变附近具有较大的低场磁熵变,对于Ni43Mn41Co5Sn11在室温1T磁场下磁熵变达到了19J.kg-.1K-1。通过调节成分,磁熵变峰值温度可以在199和294K之间调节,同时保持了较大低场磁熵变。     

Ni-Mn-Ga磁控形状记忆合金中的马氏体相变

文章采用电弧熔炼法熔炼Ni48Mn31Ga21和Ni2MnGa两种合金,并对这两种合金进行了热处理,借助交流磁化率测定、金相显微镜观察、X射线以及磁化曲线等手段研究了Ni-Mn-Ga磁控形状记忆合金中的马氏体相变。结果表明：（1）Ni48Mn3lGa21合金在室温下发生了马氏体转变,而Ni2MnGa合金在室温下则未发生马氏体转变;（2）室温下Ni2MnGa合金的饱和磁化强度比Ni48Mn3lGa21合金高;对于Ni48Mn31Ga2l合金,其马氏体态的饱和磁化强度要高于奥氏体态。     

The Ductility and Shape-Memory Properties of Ni–Mn–Ga–Cu Heusler Alloys

Metallurgical and Materials Transactions A - The effect of Cu addition on crystal structure, compressive properties and shape-memory effect of Ni50Mn25Ga25−xCux alloys was studied. With...     

Ni-Ga-Fe-Co铁磁形状记忆合金的磁性转变和马氏体相变

Ferromagnetic shape memory alloys (FSMAs) such as NiMnGa, FePd and FePt are attractive as a new magnetic actuator material. They show a large magnetic-field-induced strain of 3% - 9% due to the variant rearrangement. Recently, the present authors have reported that in the Ni-Ga-Fe alloy the martensitic transformationfrom the B2 and/or the L21 structures into a seven-layer or five-layer modulated structure occurs upon cooling. In this alloy system, however, it is impossible to obtain a martensite phase at RT with a Curie temperature (To) higher than 100℃. In this work, the effects of substitution of Co for Ni on the martensitic and magnetic transformations, crystal structures and phase equilibria in Ni-Ca-Fe alloys were studied. Ni-Ga-Fe-Co alloys were prepared by induction melting under an argon atmosphere. Small pieces of specimens were taken from the ingot and homogenized at 1433 K for 24 h followed by quenching in water. The obtained specimens were aged at 773 K for 24 h and then quenched. The compositions of each phase were determined by energy dispersion X-ray spectroscopy (El)X). The martensitic transformation temperatures and Tc were measured by differential scanning calorimetry (DSC) and vibrating sample magnetometer (VSM) measurement. The crystal structure of martensite phase was observed by X-ray diffractmeter (XRD) and transmission electron microscope (TEM). The Curie temperature Tc was increased with increasing Co content while the martensitic transformation temperature slightly decreased. In the Ni(54-x) Ga27 Fe19 Cox, Tc increases from 303 K to 408 K with increasing CO content from x=0 to x=6. The crystal structure of the martensite phase and the phase equiribria in the Ni-Fe-Ga-Co alloys will be also presented.     

哈斯勒合金Ni-Mn-Sn的磁热效应

采用真空电弧熔炼法和高温淬火法制备了四元哈斯勒合金Ni50-xCuxMn36Sn14(x=0,2,4,6)的化合物。用X射线衍射仪和振动样品磁强计研究了合金的物相与磁热效应。结果表明,部分Cu元素对Ni的替代,并没有改变三元哈斯勒合金Ni-Mn-Sn原有的晶体结构,只是晶格常数开始有减小的趋势,晶胞的体积没有发生太大的变化。M-T曲线的结果表明,该系列哈斯勒合金样品在奥氏体相的铁磁交换作用增强,导致居里温度升高,而结构相变温度降低。此外,通过麦克斯韦方程计算了该系列合金的磁熵变(-ΔSm),在磁场变化为1.5 T的情况下,获得了Ni46Cu4Mn36Sn14合金在330 K附近的最大磁熵变(-ΔSmmax)约为2.0 J·(kg·K)-1。     

Microstructure and Magnetic Properties of Ni2(Mn,Fe)Ga Heusler Alloys Rapidly Solidified by Melt Spinning

The microstructure and magnetic properties of Ni₂MnGa base alloys with “Fe” substitution in place of “Mn” are studied. The processing technique used is melt spinning at wheel speeds of 20 m/s and 30 m/s followed by annealing at 1273 K (1000 °C) for 1 hour. Fe content is varied from 2 at. pct to 11 at. pct for alloys of Ni₅₀Mn_(25?x)Fe _x Ga₂₅ with Heusler stoichiometry. Austenite with B2 partial atomic ordering and premartensitic tweed structures were found at room temperature for all the alloys at different wheel speeds. After annealing at 1273 K (1000 °C) for 1 hour, austenite phase with L2₁ Heusler atomic ordering is stabilized in samples of all the processing conditions. Saturation magnetization, martensitic transformation temperature, and Curie temperature are measured. Martensite temperature and Curie temperature increase in proportion to iron content in the alloy. Saturation magnetization is sensitive to the phase content and compositional inhomogeneities.     

Magnetocaloric Effect of Ni56Mn18.8Ga24.5 Gd0.7 Alloy

Inrecent years materials with high magnetocaloriceffect (MCE) have attracted considerable attention ow-ingto its potential application as a magnetic refriger-ant .Many material systemsthat underwentthefirst-or-der magnetic transition have been found to exhibit agiant MCE. Their typical representatives areGd5(SixGe1 -x)4[1 ,2]and La (FexSi1 -x)13[3 ,4]alloys .Ni MnGa is aferromagnetic shaped memory alloy whichundergoes a reversible first-order structural phase tran-sition (SPT) with the …     

Magnetic Transition and Magnetic Entropy Change of Gd5Si1.75Ge1.75Sn0.5

Gd5Si2Ge2.2 alloy was synthesized by arcmelting and its phase components, microstructure, and especially the line features were investigated by X- ray diffraction （XRD）, scanning-electron microscope （SEM）, energy-dispersive spectroscopy （EDS）, and transmission-electron microscope （TEM）. Gd5Si2Ge2.2 consists of Gd5Si2Ge2-type and GdGe-type phases and presents eutectic characteristics. There are many regular line features on the Gd5Si2Ge2-type phase according to SEM. EDS shows that the line feature is not the Gd5 （Si,Ge）3-type phase because Gd content decreases at the line features. Two types of line features are found in the fine microstructure of Gd5Si2Ge2-type phase by TEM. Selected area diffraction （SAD） confirms that both line features are not the secondary phase or twins. There is no changes observed in the microstructure of Gd5Si2Ge2 2 from room temperature to 1400 ℃ with in situ high temperature optical microscope, therefore, it is deduced that the line features observed by SEM are formed during the solidification.     

Fe对Ni-Mn-Ga形状记忆合金相变和力学性能的影响

研究了Fe含量对Ni₅₆Mn_25-xFe_xGa₁₉(x=0~10)合金的微观组织结构、相变行为、力学性能和记忆特性的影响规律.当x ≤ 4时,Ni₅₆Mn_25-xFe_xGa₁₉合金仍然保持着单一的四方结构马氏体相;当x ≥ 6时,合金呈现为马氏体相和面心立方γ相组成的双相结构.相对于马氏体相,γ相为富Ni和富Fe相,其含量随Fe含量的增加而增加.随着Fe含量增加,合金的马氏体相变温度逐渐降低,其峰值温度从x=0时的356℃降低至x=10时的170℃,这主要归因于马氏体相尺寸因素和电子浓度的综合作用.通过添加Fe替代Mn在合金中引入的γ相可提高合金的强度和塑性,但最大形状记忆回复应变从x=0时的5.0%降低到x=6时的2.0%.      

Ni48Mn33Ga18Tb1合金的马氏体相变和磁性形状记忆效应

本文研究了 Ni48Mn3 3 Ga1 9合金添加微量的稀土元素 Tb后 ,对合金的马氏体相变、磁致应变性能及抗弯性能的影响 ,发现合金的马氏体相变温度、磁致应变值有所下降 ,而机械抗弯强度有显著提高。     

Magnetic contribution to the interdiffusion coefficients in bcc (<Emphasis Type="Italic">α</Emphasis>) and fcc (<Emphasis Type="Italic">γ</Emphasis>) Fe-Ni alloys

The interdiffusion coefficients in bcc (α) and fcc (γ) Fe-Ni alloys below their Curie temperatures have been calculated based on the magnetic contribution to the free energy for interdiffusion. The free energy for interdiffusion due to magnetic ordering in bcc Fe-Ni alloys is positive. The calculated interdiffusion coefficients in bcc Fe-Ni alloys fit the experimental data quite well. In fcc Fe-Ni alloys, the magnetic contribution to interdiffusion depends on both temperature and composition and is abnormal for Ni compositions in the Invar region. The free energy of vacancy formation is positive and the free energy of vacancy migration is negative, due to the effect of magnetic ordering. The interdiffusion coefficient in the ferromagnetic phase is lower than that extrapolated from the paramagnetic phase for Ni compositions of 50 at. pct and greater and is higher than that extrapolated from the paramagnetic phase for Ni compositions of 40 at. pct and lower.     

Electron Concentration Dependence of Transformation Temperature in Different NiMnGa Alloys with First Order Magnetic Transition

Electron Concentration Dependence of Transformation Temperature in Different NiMnGa Alloys with First Order Magnetic Transition     

Phase Structure and Electrochemical Characteristics of Ml（Ni3.55Co0.75Mn0.40Al0.30）5x （x=0.88, 0.92, 0.96, 1.00） Hydrogen Storage Alloys

The phase structure and electrochemical characteristics of Ml （（Ni3.55Co0.75Mn0.40Al0.30）sx （ x = 0.88, 0.92, 0.96, 1.00） hydrogen storage alloys were studied. The effect of the stoichiometric ratio on the phase structure and electrochemical characteristics was analyzed. The results of XRD reveal that all the alloys consist mainly of LaNi5 phase with the hexagonal CaCu5 structure. But a few of the diffraction peaks of La2Ni7 phase on XRD pattern are observed when x ≤ 0.92, and with decreasing x, the intensity of La2Ni7 diffraction peaks increases and the values of lattice parameters a and cell volume increase, c and c/a of LaNi5 phase decrease gradually. When x≥0.96, La2Ni7 phase disappears and the alloys become single CaCu5-type. The electrochemical tests show that the maximum discharge capacity, high rate dischargeability and low temperature dischargeability are improved to different degrees by adjusting the stoichiometric ratio.     

含铽多晶Ni-Mn-Ga磁性记忆合金的大磁感生应变

研究了含稀土Tb的多晶Ni50Mn29Ga21磁性形状记忆合金的磁感生应变效应。在一定的应力状态下，可获得-1．1％的大磁感生应变。稀土在明显地细化晶粒和提高材料力学性能的同时，不影响马氏体孪晶界面的运动，反而使应力作用下的磁感生应变效应进一步提高，使材料更具有实用性。     

Effects of Sm on Phase Transformation in Ni-Mn-Ga Alloys

The effects of small amount additions of Sm on the martensitic transition and magnetic phase transition of polycrystalline Ni-Mn-Ga alloys were investigated. The experimental results show that the Sm doped alloys also undergo a thermal-elastic martensitic transformation and reverse transformation during cooling and heating process and the addition of Sm decreases the martensitic transformation temperature and Curie temperature in different degree respectively. Ni-Mn-Ga alloys of adding Sm still possess Heusler structure, but their crystal lattice parameters are modified slightly. The addition of a proper amount of Sm does not basically decrease Tc of the alloy when avoiding the appearance of second phase. In addition, the doped alloys have favorable toughness because of grain refinement of Sm.     

Effect of Surface Tension on Gas Atomization of a CrMnNi Steel Alloy

The aim of the current research is the experimental investigation of the mass median particle size d₅₀ as a function of surface tension for liquid Cr–Mn–Ni steel alloy with 16% Cr, 7% Mn, and 9% Ni. To modify the liquid steel design sulfur was add to the Cr–Mn–Ni steel in five steps up to a 1000 mass ppm. The surface tension of the liquid steel alloy was measured using maximum bubble pressure method and yttria stabilized capillary in a temperature range from 1701 to 1881 K. In addition, the same steel charges were sprayed to steel powder using a vacuum inert gas atomization using pure argon gas. The increase of sulfur in Cr–Mn–Ni steel will decrease the surface tension to 0.91 N m^?1. The temperature coefficient of surface tension is positive for all investigated Cr–Mn–Ni alloys due to a sulfur content ≥100 mass ppm. The final mass median particle size d₅₀ decreases from 54.3 µm for AISI 304 reference steel alloy to 17.1 µm for Cr–Mn–Ni steel alloy (16‐7‐9 S10) with the highest sulfur content and the lowest surface tension of all investigated liquid steels. It is concluded from the present work that surface tension is the decisive factor in adjusting d₅₀ at a constant spraying parameters.     

Ti50Ni16Cu25Nb9阻尼合金的研制

Ti50Ni16Cu25Nb9是在TiNiCu阻尼合金的基础上发展的一种新型阻尼合金。X射线衍射（XRD）和能谱（EDS）分析表明,Nb的加入使B如Ti50Ni16Cu25Nb9合金在凝固过程中发生共晶反应,生成单斜结构的B19′马氏体和fcc结构β-Nb相。晶粒内部为富Ni贫Cu马氏体与β-Nb相的共晶组织,晶间为富Cu贫Ni相,合金中存在明显的微观偏析。高温固溶热处理可以改善合金的微观偏析,但是随着热处理温度的增加,β-Nb软化相有球化趋势,相含量减少,不利于优化合金的阻尼性能。900℃×2h＋WQ热处理可以明显改善合金的微观偏析,并保留适量的条状β-Nb相。     

Experimental Evidence of the Effect of Alloying Additions on the Stagnant Stage Length During Cyclic Partial Phase Transformations

Cyclic phase transformation experiments are performed in a series of Fe-C-xMn, Fe-C-Mn-xNi, and Fe-C-Mn-xCo alloys to study the effect of alloying elements on the length of the stagnant stage during a cyclic partial phase transformation in the austenite–ferrite two-phase region. The length of stagnant stage increases linearly with the increasing Mn or Ni concentration, while Co has no effect. It was experimentally proven that the effects of alloying elements on the length of stagnant stage are additive, and the experimental results matched the predictions of the local equilibrium model very well.