Ni50Mn27Ga23快淬薄带的马氏体相变和磁感生应变

采用快淬技术制各了非化学计量成分的Ni50Mn27Ga23多晶薄带，对快淬薄带的马氏体相变和磁感生应变进行了研究。结果表明，快淬薄带侄冷却和加热过程中仍然发牛热弹性马氏体相变及逆相变，具有典型的热弹性形状记忆效应，并且比铸态合金具有更大的应变，但是马氏体相变温度下降。快淬工艺在合金内部引入特定的内应力，使薄带形成织构，是合金获得更大相变应变和磁感卞应变的原因。热处理后，内应力大大降低，导致磁感牛应变降低。     

预变形对Ni-Mn-Ga合金马氏体相变的影响

研究了形变对Ni-Mn-Ga合金马氏体相变及其组织形态的影响，并应用马氏体相变热力学和动力学探讨了适当塑性变形后马氏体相变滞后得以大幅度提高的微观本质。结果表明，随着应变量的增加，马氏体相变温度几乎保持不变，而其逆相变温度则迅速升高，塑性应变导致储存在界面处的弹性应变能的释放是塑性变形提高合金相变滞后的主导因素。     

Co影响Ni-Mn-Ga合金马氏体相变的第一性原理分析

采用基于密度泛函理论的第一原理平面波赝势法,研究了掺杂Co元素对Ni-Mn-Ga磁性形状记忆合金的能态密度分布的影响规律,阐明了Co对马氏体相变作用机理.研究表明,随Co含量增加,更多的Co3d-Mn3d杂化取代了Ni3d-Mn3d杂化,使母相稳定性提高,马氏体相变温度降低.Co的加入对Ni-Mn-Ga-Co母相的自旋向上能态密度几乎没有影响,但明显改变自旋向下能态密度.     

预形变对Fe-Mn-Si合金γε相变的影响

预形变强烈诱发Ｆｅ－Ｍｎ－Ｓｉ合金产生γ→ε马氏体相变.预形变量较小时,形变诱发产生的γ→ε马氏体具有择优取向,同一晶粒内的ε马氏体片大多数取向相同;随预形变量增大,ε马氏体大量增多,ε马氏体片之间呈现交叉;预形变量越大,交叉现象愈严重,形变诱发的ε马氏体片的相互交叉是产生加工硬化的重要原因之一．预形变对Ｆｅ－ Ｍｎ－Ｓｉ合金εγ相变过程的相变温度影响显著,随着预形变量的增大,合金的相交点Ｍｓ有不同程度升高,且含Ｓｉ量越多,升高幅度越大;Ａｓ和Ａｆ都明显升高,其升高幅度更为显著．     

外加拉应力对TiNi合金马氏体相变点Ms的影响

采用四点接线电阻法测定了外加拉应力作用下燃烧合成Ｔｉ５０Ｎｉ（ａｔ％）形状记忆合金马氏体相变点Ｍｓ的变化,并从宏观热力学和微观相变动力学两方面综合分析外力对ＴｉＮｉ合金马氏体相变点Ｍｓ的影响。在再结晶退火ＴｉＮｉ合金中,马氏体／母相界面间保持良好共格关系,外力的宏观热力学作用可使Ｍｓ上升,而从微观动力学方面看,外力可破坏界面的共格性,使界面可动性及Ｍｓ下降,两者作用相互抵消的结果导致Ｍｓ随外力增加变化不大;而在冷加工后回复退火ＴｉＮｉ中仍存在大量冷加工位错,其马氏体／母相界面间的共格性已遭到这些位错的明显破坏,外力通过微观相变动力学作用使Ｍｓ下降的趋势已很小,而主要是通过热力学作用使Ｍｓ值明显上升。     

多晶Ni-Mn-Ga磁性记忆合金中间马氏体相变研究

用内耗分析方法研究了Ni-Mn-Ga磁性记忆合金的相变行为。发现多晶材料也存在着由温度诱发的完整的热弹性中间马氏体相变。在发生中间马氏体相变过程中，内耗明显增高，同时，弹性模量发生突变，表明相变前和相变后材料的模量有较大的差异。在相变过程中没有观察到软模现象。     

Ni50Mn26Ga24-yFey（y=0-23）磁性形状记忆合金的相变

制备了以Fe代Ga的Ni50Mn26Ga24-yFey（y=0-23）系列合金，研究了掺杂元素Fe对合金的马氏体相变温度、居里温度及相结构的影响，确定了合金成分与相变之间的变化规律。结果表明：掺杂元素Fe对Ni-Mn-Ga合金的马氏体相变的影响较为显著，当Fe含量（原子分数，下同）y≥12时，合金不显示热弹性马氏体相变过程，在具有母相结构的基础上有明显的第二相析出。合金的M5随Fe含量的增加而增加，合金的Tc随e／a的增大而增大。     

快淬Fe—Cr—Mo—Si—B非晶合金中的相分离

透射电镜观察到非晶Ｆｅ６５Ｃｒ１８Ｍｏ２Ｓｉ１Ｂ１４和Ｆｅ６２Ｃｒ１８Ｍｏ２Ｓｉ１ｂ１７基体中分布着纳米级颗粒状的非晶第二相。磁测量与Ｍｏｓｓｂａｕｅｒ谱显示出非晶样品由少量铁磁相与顺磁基体相组成，并表现出单畴颗粒的高矫顽力。快淬过程中这冷液体里硼的偏聚导致非晶合金中非晶第二相的形成及脆化。     

Role of magnetism on the martensitic transformation in Ni-Mn-based magnetic shape memory alloys

The effect of magnetism on the martensitic structural transformation has been analyzed through the evolution of the transformation temperatures of several Ni-Mn-Ga and Ni-Mn-In alloys subjected to high-temperature quenching and post-quench annealing thermal treatments. It is found that the atomic order variations associated with the thermal treatments affect the structural transformation in different ways depending on the character of the magnetic ordering in the austenitic and the martensitic phases. In particular, regardless of composition, the variation in the atomic order affects the martensitic transformation temperature only in those alloys in which at least one of the structural phases show magnetic order at the transformation temperature, whereas those transformations taking place between paramagnetic phases remain unaffected. The observed behaviors are explained in terms of the effect of the magnetic exchange coupling variations on the free energy difference between austenite and martensite. The results confirm the key role of magnetism in the martensitic transformation.     

Effect of post annealing on phase transformation of Ni-Mn-Ga ferromagnetic shape memory alloy particles prepared by ball milling

The effect of post annealing on the phase transformation of Ni52Mn24Ga24 ferromagnetic shape memory alloy particles prepared by ball milling was studied. Ni52Mn24Ga24 alloy particles at micron scale were prepared successfully by ball milling the crushed bulk alloy. SEM observation reveals that the shape of the as-milled particle is regular polygon and a lot of cracks can be seen at the surface of the particles. For as-milled particles, the widening of characteristic peak can be found in the XRD pattern, and no transformation characterization can be detected by DSC. Post annealing at the elevated temperature will recover the transformation behavior of milled particles to the same level as that of bulk sample. It is shown that with increasing annealing temperature above 400 ℃, Ms decreases and As increases, while the magnetic transition temperature keeps constant. XRD results indicate that the change of grain size of the particles results in such an effect of post annealing.     

Structural transition of Ni-Mn-Ga ferromagnetic shape memory alloy particles prepared by ball milling

The size, crystal structure and phase transformation of Ni49.8Mn28.sGa21.7 alloy particles prepared by planetary ball milling （PBM） and vibration ball milling （VBM） were investigated by SEM, XRD and DSC. The results show that the particles milled by PBM for 4 h exhibit irregular polyhedron, with the size distribution between 5 pm and 40 pm. These particles present disordered fct structure with no phase transformation behaviour. When annealed at 600℃ for 1 h, the crystal structure of the particles evolves from disordered fct to Heusler completely. The particles milled by VBM for 4 h exhibit flaky shape, with the size distribution from 3 μm to 30μm. The particles present disordered fcc structure with no phase transformation behaviour. However the crystal structure of these particles doesn＇t transform from disordered fcc to Heusler completely aider annealing at 600 ℃ for 1 h, for the severe lattice distortion induced in the VBM process is not eliminated entirely.     

Effects of Tb addition on the microstructure and properties of a Ni-Mn-Ga ferromagnetic shape memory alloy

The effects of terbium addition on the microstructures and properties of polycrystalline Ni_48.8Mn_29.7Ga_21.5 alloy (numbers indicate at.%) were investigated. The results show that the grain size of Ni-Mn-Ga alloy decreases significantly with the addition of Tb, and Tb elements are found to exist in the grain boundary region and form a (Ni, Tb)-rich quaternary phase. The compressive ductility and fracture toughness increased with the addition of Tb. The improvement of mechanical properties and the slight change of martensitic transformation temperature and the magnetic properties of the Tb-added alloys are discussed in terms of the modification of microstructures with the addition of Tb.     

冷却速度对Fe-4Cr合金奥氏体—铁素体相变的影响

通过高精度差分膨胀仪记录了Fe-4Cr合金在连续冷却过程中的线膨胀行为,获得其在不同冷速（75、150和330 K/min）下奥氏体→铁素体相变的相关动力学信息,并利用相变动力学模型解析式拟合了Fe-4Cr合金转变体积分数随温度变化的实验曲线。研究表明：冷却速度主要是通过改变晶界之间的位相角来影响动力学参数,即生长激活能QG和指前因子v0,从而影响奥氏体→铁素体相变动力学。     

The mathematical modeling of phase transformation of steel during quenching

In the heat treatment of steel, uneven cooling in variably introduces residual stresses in the workpiece. These residual stresses can combine with the thermomechanical stresses encountered in operation to cause premature fatigue failure of the material. A prediction of the residual and thermoelastoplastic stresses developed during heat treatment would be beneficial for component design. In this article a numerical model is developed to predict the thermoelastoplastic and residual stresses during rapid cooling of a long solid cylinder. The total strains developed during cooling of the cylinder comprise elastic, thermal, and plastic strains and strains due to phase transformation. For plastic deformation an extension of Jiang’s constitutive equations developed by Jahanian is adopted. The properties of the material are assumed to be temperature dependent and characterized by nonlinear strain hardening. For phase transformation two parts are considered: nucleation according to Scheil’s method and phase growth according to Johnson and Mehl’s law. For martensitic transformation, a law established by Koisteinin and Marburger is used. Non-additivity of pearlitic and bainitic nucleation suggested by Manning and Lorig is taken into account by means of a correction factor to Scheil’s summation of the transition from pearlitic to bainitic. The effect of phase transformation and temperature dependence of material properties is investigated. It is shown that by neglecting the temperature dependency and phase transformation in numerical calculations, the results are underestimated. The numerical results are compared with the available experimental data in the literature, and good agreement is observed.