EFFECT OF MAGNETIC FIELD ON MARTENSITIC TRANSFORMATION IN Fe-21Ni-4Mn ALLOY

The pulsed magnetic field induced martensitic transformation with isothermal and athermal kinetics in Fe-2Ni-4Mn(wt-%)alloy has been studied by means of magnetization measurements,optical microscopy and thermodymical analyses.It is shown that there exits a critical magnetic intensity for induing martensitic transformation at a given temperature above Ms.The critical magnetic field increases linearly with increasing ΔT= T-M_S.The magnetic field strongly promotes the athermal martensitic transforamtion and restrains the isothermal one.The entropy change ΔS for athermal transformation at Ms is 4.13 J/mol· K.The effect of magnetic field on martensitic transformation in Fe-21Ni-4Mn alloy is main- ly due to Zeeman effect.Lath,plate and butterfly martensities were observed under magnetic field.     

F6-21Ni-4Mn合金强脉冲磁场诱发马氏体相变的研究

采用磁性测量、光学金相和强脉冲磁场,研究了Fe-21Ni-4Mn合金的磁场诱发马氏体相变。发现在M_s点以上,当施加的磁场高于某一临界值(临界磁场)时,便能诱发马氏体相交;临界磁场随温度的升高而增加,并与ΔT(T-M_s)成直线关系;脉冲磁场强烈地促进变温转变,抑制等温转变;磁场对Fe-21Ni-4Mn合金的马氏体相变作用主要是Zeeman效应,求得在M_s点变温的熵变ΔS_(M_S)~(1t)为·13J/mol·K·同时发现磁场诱发的马氏体形貌为板条伏、片状和蝶状,其形成量随施加的最大磁场强度成线性增加。     

Ni52Mn21+xGa27-x(x=0-5)磁性形状记忆合金的相变

研究了非化学计量成分的多晶Ni52Mn21+xGa27-x(x=0-5)系列合金的热弹性马氏体相变和磁相变.合金的马氏体相变温度Ms随Mn含量的增加而升高,当x＞4时,Ms已经升高到室温以上,而马氏体相变滞后△T随z的增大而减小;合金的磁相变温度TC随z增加而升高,但变化范围不大,在z＞2后,Tc保持在348 K左右.实验获得了一种具有实用前景的合金成分--Ni52Mn25Ga23合金,其马氏体相变温度在室温以上,相变滞后仅为5 K.     

Effect of a magnetic field on the reverse and forward martensitic transformations in the Fe-33% Ni alloy

Effect of a magnetic field on the reverse and forward martensitic transformation in an iron-nickel alloy with the temperature of the start of the α-γ transformation that is close to the Curie temperature of the γ phase has been studied. The result obtained is explained by the mutual compensation of two mechanisms of the effect of a magnetic field on the reverse martensitic transformation in this alloy. The role played by the magnetic state of austenite in the realization of the corresponding kinetics of the martensitic transformation in the iron-based alloys with a mixed kinetics is discussed.     

Martensitic transformation of Ti-18Nb(at.%) alloy with zirconium

The addition of 3%～9% Zr on the martensitic transformation of Ti-18Nb(at.%) alloy was investigated. The results of microstructure and X-ray diffraction (XRD) analysis show that the phase constitution of as-quenched Ti-18Nb-9Zr(at.%) alloy consists of the retained matrix and martensite, while that of the other three alloys is single martensite. No trace of athermal phase was found in any of the as-quenched alloys. Unlike the effect of Nb addition on the martensitic transformation start temperature Ms of Ti-1...     

Isothermal and athermal martensitic transformations in Ni–Ti shape memory alloys

Ni–Ti shape memory alloys are known to demonstrate three possible transformation paths between B2 and B19′ phases, B2–R–B19′, B2–B19′ and B2–B19–B19′, depending on their composition and thermo-mechanical treatment. In this work the isothermal kinetics of accumulation of martensite/austenite for all types of martensitic transformations in Ni–Ti and Ni–Ti–X (X = Fe or Cu) has been studied by means of resistance measurements during interruption of cooling/heating scans. Experimental results show that all transformations to the B19′ phase (B2–B19′, R–B19′, B19–B19′) demonstrate a substantial isothermal accumulation of martensite during isothermal dwelling between the martensitic transformation start and finish temperatures. The reverse transformations B19′–R and B19′–B19 are also classified as isothermal. The isothermal accumulation of austenite detected during the reverse B19′–B2 transformation is much less intense, at least partially due to the low sensitivity of resistance to the martensite fraction variation during the reverse transformation, and remains comparable with the resolution of the experimental set-up. The transformations between the B2 and R as well as between the B2 and B19 phases are athermal. Analysis of the entire set of possible transformations in β Ni–Ti systems allows one to conclude that isothermal transformations possess a much broader hysteresis and transformation range compared with athermal ones. Since the hysteresis of the transformation is related to the friction forces acting on interfaces this fact, and also observation of the isothermal effects during reverse martensitic and intermartensitic transformations, strongly support the interpretation of the observed isothermal effects in Ni–Ti as due to the diffusionless but thermally activated motion of interfaces during transformation. The difference between the transformation to B19′ martensite (isothermal) and all others (athermal) is attributed to a distinction in strain accommodation.     

Volume Change During Intermartensitic Transformations in Ni-Mn-Ga Alloy

Characteristics of phase transitions in Ni₅₄Mn₂₄Ga₂₂ alloy were studied at different hydrostatic pressures to shed light on the nature and mechanisms of intermartensitic transformations. The temperature dependence of resistivity of the alloy was used to find characteristic temperatures of martensitic and intermartensitic transformations as a function of hydrostatic pressure. The latent heat of these transformations was determined by differential scanning calorimetry. The transformation volume effects were calculated using Clausius-Clapeyron equation. They make up 0.082% for martensitic and 0.024% for intermartensitic transformations.     

Phase transformations in powder iron-nickel alloys produced by mechanical alloying

Phase transformations in Fe-Ni alloys produced by mechanical alloying have been investigated by X-ray diffraction, Mössbauer spectroscopy, and magnetometric methods. The critical temperatures of phase transformations during heating and cooling of the alloys in the concentration range of 12–26 at % Ni have been determined, and the intervals of existence of phases at room temperature have been established. In the alloys that contain less than 16 at % Ni, a “normal” (diffusion-controlled) γ-α transformation was observed. In some alloys, an isothermal γ-α₂ martensitic transformation has been revealed, which was not earlier observed in cast Fe-Ni alloys. A considerable reduction in the start temperatures of the martensitic transformation in comparison with the cast alloys of the same nominal compositions has been found. Factors are considered that are responsible for the observed values of the temperatures of diffusionless transformations in the mechanically alloyed materials.     

Phase transformations in Ni-Mn-In-based alloys in magnetic field

The effect of a high-strength magnetic field on the phase transformations of ferromagnetic materials based on the Ni-Mn-In system with different degrees of alloying has been revealed experimentally. The effect of the chemical composition of the alloys and magnetic treatment on the martensitic transformations and magnetic transitions has been investigated. It has been established that, upon substituting nickel atoms with manganese atoms, the temperature of the martensitic transformation decreases.     

Multiple steady state phenomenon in martensitic transformation

1　ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｍａｒｔｅｎｓｉｔｉｃｔｒａｎｓｆｏｒｍａｔｉｏｎｈａｓｂｅｅｎｏｎｅｏｆｔｈｅｍｏｓｔａｃｔｉｖｅｆｉｅｌｄｓｉｎｃｏｎｄｅｎｓｅｄｍａｔｔｅｒｐｈｙｓｉｃｓｆｏｒｍａｎｙ ｙｅａｒｓ.Ａｎｕｍｂｅｒｏｆｔｈｅｏｒｅｔｉｃａｌｍｏｄｅｌｓｈａｖｅｂｅｅｎｐｒｏｐｏｓｅｄｔｏｕｎｄｅｒｓｔａｎｄｔｈｅｐｈｙｓｉｃａｌｎａｔｕｒｅｏｆｔｈｅｍａｒｔｅｎｓｉｔｉｃｔｒａｎｓｆｏｒｍａｔｉｏｎ[1～ 6 ] .Ｈｏｗｅｖｅｒ ,ａｓｙｅｔｔｈｅｒｅｉｓｎｏｔａｇｅｎｅｒａｌｓａｔ…     

Effect of Co addition on martensitic phase transformation and magnetic properties of Mn50Ni40-xIn10Cox polycrystalline alloys

This study investigated the use of Co to enhance the magnetic driving force for inducing the martensitic transformation of Mn₅₀Ni_40-xIn₁₀Co_x alloys. These alloys present a martensitic transformation from a Hg₂CuTi-type austenite to a body centered tetragonal martensite, with a large lattice distortion of 15.7% elongation along the c direction and 8.2% contraction along a and b directions. The martensitic transformation temperatures, transformation enthalpy and entropy changes decreased with increasing the Co content in these alloys. The maximum magnetization of the austenite increased significantly, whereas that of the martensite changed much less prominently with increasing the Co substitution for Ni, leading to increase of the magnetic driving force for the transformation. The magnetization increase of the austenite is found to be due to (i) formation of ferromagnetically coupled Mn–Mn due to new atomic configuration in off-stoichiometric composition, (ii) magnetic moment contribution of Co and (iii) widening of the temperature window for magnetization of the austenite by lowering the temperature of the martensitic transformation. These findings clarify the effect of Co addition on martensitic transformation and magnetic properties in Mn-rich ferromagnetic shape memory alloys, and provide useful understanding for alloy design for magnetoactuation applications.     

Magnetic-field-induced martensitic transformations in Ni47 − x Mn42 + x In11 alloys (with 0 ≤ x ≤ 2)

Magnetic properties and martensitic transformations in the Ni_{47 ? x} Mn_{42 + x} In₁₁ alloys (with 0 ≤ x ≤ 2) have been studied. The magnetic-field-induced martensitic transformation was found to be observed for all the alloys. The critical temperatures of magnetic and structural phase transformations, temperature dependences of spontaneous magnetization of austenite and martensite, and the critical field, at which the martensitic transformation occurs, have been determined based on magnetic measurements performed for the alloys under study. The spontaneous magnetization of the alloys in the martensitic state has been shown to be lower than that in the magnetic-field-induced austenitic state by a factor of six.     

第二相对等径弯角挤压处理TiNi合金和Ti-Mo基合金力学性能及马氏体转变的影响

借助ECAP技术对TiNi合金和Ti-Mo基记忆合金在673~773K进行挤压处理,挤压路径为Bc,以获得超细晶组织,从而增强母相的强度,改进材料的性能。研究热力学稳定相及亚稳相对这两种合金的力学性能和马氏体转变的影响。结果表明,对于富钛TiNi合金,热力学稳定相Ti2Ni对马氏体转变及超弹性没有影响,而稳定相α相则可造成Ti-Mo-Nb-V-Al塑性降低。亚稳Ti3Ni4相对富镍TiNi合金的R相变、马氏体转变及超弹性有很大影响。并对第二相对TiNi合金和Ti-Mo基合金力学性能、马氏体转变的影响进行分析。     

PHASE TRANSFORMATIONS IN RAPIDLY SOLIDIFIED TiNi SHAPE MEMORY ALLOYS

ＰＨＡＳＥＴＲＡＮＳＦＯＲＭＡＴＩＯＮＳＩＮＲＡＰＩＤＬＹＳＯＬＩＤＩＦＩＥＤＴｉＮｉＳＨＡＰＥＭＥＭＯＲＹＡＬＬＯＹＳＷａｎｇ；ＳｈｉｄｏｎｇＷｕ；Ｘｉａｏｚｈｅｎ（ＡｎａｌｙｔｉｃａｎｄＴｅｓｔｉｎｇＣｅｎｔｅｒ．ＳｏｕｔｈｅａｓｔＵｎｉｖｅｒｓ...     

Influence of carbon on martensitic phase transformations in NiTi shape memory alloys

In the present paper we show how carbon affects martensitic transformations in Ni-rich NiTi shape memory alloys. During vacuum induction melting in graphite crucibles, NiTi melts dissolve carbon and TiC particles form during solidification. Differential scanning calorimetry (DSC) shows that this is associated with a decrease in the phase transition temperatures. We provide new experimental evidence for increasing temperature intervals between the start and the end of the martensitic transformations (from B2 to B19′) with increasing C content in as-cast and solution-annealed (850 °C) microstructures. The nucleation and growth of TiC particles in intercellular/interdendritic regions causes variations in the local Ni/Ti ratios. This results in wider transformation temperature intervals (DSC peak broadening) in as-cast and solution-annealed microstructures. Subsequent intense heat treatments (1000 °C) homogenize the alloy and re-establish sharp DSC peaks during martensitic transformations.     

马氏体相变

对前人所下的马氏体相变定义和所作的分类进行了总结,将马氏体相定义为：替换原子经无扩散切变位移（均匀的和不均匀的形变）由此产生形状改变和表面浮突,呈不变平面应变特征的一级,形核一长大型的相变,马氏体要变按动力学分为变温相变和等温相变,按热力学和界面动态分为弹性相变,近似（半）热弹性相变和非热弹性相变,热弹性相变的判据为（１）临界项相变动动力小,热滞小;（２）相界面能往复（正,逆）运动;（３）形状应变     

Effect of atomic ordering on the phase transformations in Ni–Mn–Ga shape memory alloys

The influence of the L2₁ order degree in single crystalline Ni–Mn–Ga alloys is analysed in the present work. The alloys studied display a sequence of martensitic (MT) and intermartensitic (IMT) transformations on cooling, the reverse transformation to austenite, on heating, taking place in a single step. Quenching from different temperatures produces distinct effects on the MT and IMT: while the MT temperatures are not practically affected by the performed heat treatments, the IMT shifts towards lower temperatures after quenching from increasing temperatures. Such evolution can be related to changes in the L2₁ order degree, in the sense that ordering favours the occurrence of the IMT while it hardly affects the MT temperatures. The closeness of the free energies of the different martensitic structures and the differences between the MT and IMT entropy changes allow this behaviour to be explained. In turn, the Curie temperature increases with the L2₁ ordering for an alloy undergoing magnetic transition in martensite phase, no changes being detected if the Curie temperature is above the martensitic transformation.     

徐祖耀院士的学术贡献

论述了徐祖耀院士在马氏体相变、贝氏体相变及形状记忆材料方面的学术贡献。其中包括：揭示了无扩散马氏体相变中存在间隙原子（或离子）的扩散;完善了铁合金马氏体相变的热力学;解决了计算Fe-C合金相变开始温度（Ms）的难题;以孤立子理念演算和阐释了相变驱动力与马氏体长大速率之间的关系;以群论研究了形状记忆合金热弹性马氏体相变的对称性并建立了计算热弹性马氏体对称分布的数学模型;创建了铜基合金马氏体相变和贝氏体相变热力学;认证了陶瓷中存在贝氏体相变。     

MAGNETIC--FIELD--CONTROLLED SHAPE MEMORY EFFECT AND SUPERELASTICITY OF Ni53.2Mn22.6Ga24.2 SINGLE CRYSTAL

证实了Ni_53.2Mn_22.6Ga_24.2单晶发生的两步马氏体相变行为是完全热弹性的. 在磁场作用下, 该材料的马氏体相变和中间马氏体相变展现出相同的应变特征, 且具有磁控双向形状记忆效应. 磁场下应力--应变特性的测量结果表明, 磁场不但对压应力诱发马氏体相变过程中变体重取向所需应力的大小有影响, 而且使原来不可逆的形变成为可逆, 这种磁控超弹性特性预示了该合金用作磁控超弹性元器件材料的可能性.     

Wear resistance of alloys of the Cu-Al-Ni system with martensitic transformation under conditions of sliding friction

Wear processes that occur under conditions of sliding friction in alloys of the Cu-Al-Ni system with martensitic transformation are studied. The effect of the initial structure of the alloys on their wear resistance in investigated. Advantages of the alloys with martensitic transformation over traditional tribotechnical materials, i.e., standard bronzes BrOTsS 5-5-5 and BrAZh 9-4, are described.