Cu对Ni50Mn36In14相变和磁性的影响

文章研究了Cu替代部分Ni对铁磁性形状记忆合金Ni₅₀Mn₃₆In₁₄相变和磁性的影响规律. 研究表明,在Ni_50-xCu_xMn₃₆In₁₄中,随着Cu含量的增加,相变温度逐渐降低. Cu含量低于5%时,奥氏体的磁性强于马氏体的磁性, 母相和马氏体相的饱和磁化强度的差值ΔM随着Cu含量的增加而增大. 当Cu含量x=4.5时, ΔM迅速增加到80 emu/g, 并在该材料中观察到了磁场驱动的马氏体到奥氏体的转变,显示了该材料作为磁驱动磁电阻材料的潜在应用前景.当Cu含量高于5%时,奥氏体保持铁磁状态, 马氏体相由反铁磁状态变为铁磁状态,马氏体的磁性强于奥氏体的磁性, ΔM大大削弱,磁场驱动性质消失.     

针状纳米MnxNi0.5-xZn0.5Fe2O4的共沉淀法制备及表征

通过在碱液中共沉淀Mn²⁺、Ni²⁺和Fe²⁺后制备了棒状的前躯体,前躯体于不同温度煅烧后制得了Mn_xNi_0:5-xZn_0:5Fe₂O₄棒状体. 利用X射线衍射仪和透射电镜对棒状体的物相、形貌及粒径进行了表征,并利用振动样品磁强计对磁性能进行研究. 结果表明长径比大于15的棒状,随着x值的增加,Mn_xNi_0:5-xZn_0:5Fe₂O₄样品的直径增加,长度下降,长径比变小,当x=0.5时其直径在50 nm左右而长径比减小到7～8. 随着x值的增加,样品的矫顽力先增加后减少,x值达到0.4时样品的矫顽力再次增加,当煅烧温度为600 oC,x=0.5时样品的矫顽力最大为134.3 Oe. 饱和磁化强度随着x值的增加先增加后减少,当煅烧温度为800 oC和x=0.2时达到最大为68.5 Oe.     

内应力对Mn2NiGa铁磁形状记忆合金的结构、相变和磁性能的影响

通过施加压应力的方法,在铁磁形状记忆合金Mn₂NiGa中引入残留内应力,研究了内应力对 Mn₂NiGa材料的结构、相变和磁性能的影响.研究发现,加压过程使材料发生了塑性形变,在材料内部引入了大量的位错缺陷.卸载后保留的位错缺陷在材料中造成了残留的内应力,导致了马氏体相变温度大幅度提高, 使原本室温下的母相转变成了马氏体相.测量到导致样品转变成马氏体的阈值压应力为1.0 GPa.加压形成的马氏体中的残留内应力将矫顽力从低于50 Oe提高到350 Oe.残留内应力在730 K的热处理中由于位错缺陷的消失而得以消除,样品实现了马氏体逆相变.如此高的逆相变温度使得 Mn₂NiGa马氏体的居里温度测量成为可能,获得了530K的数值.     

Fe合金FCC-BCC原子尺度台阶型马氏体相界面迁移行为的分子动力学模拟研究

两相界面的原子尺度结构对相界面迁移行为具有重要影响.高分辨透射电子显微分析表明钢中马氏体相界面具有高度为若干原子层间距的台阶结构,然而目前Fe合金马氏体相变的模拟研究工作中绝大多数使用非台阶型相界面结构作为模拟初始模型.本文基于拓扑模型和相变位错理论构建了Fe合金FCC/BCC台阶型相界面初始模型,采用分子动力学模拟方法研究了Fe合金马氏体相界面的迁移行为.研究结果表明,当两相界面具有约束共格匹配关系及台阶结构时,体系发生FCC→BCC马氏体相变并呈现典型的非扩散切变特征;相变过程中FCC/BCC宏观尺度相界面沿其法线方向以(4.4±0.3)×10~2 m/s的速度迁移,且相界面在迁移过程中始终保持稳定的台阶结构和相对平直的宏观界面形貌特征;相变位错的滑移速度高达(2.8±0.2)×10~3 m/s,相变位错阵列沿台阶面的协同侧向滑移不仅是马氏体台阶结构宏观相界面迁移的微观机制,也是马氏体相变宏观形状应变的主要来源;采用分子动力学模拟方法获得的Fe合金马氏体相变晶体学特征参量与拓扑模型的解析解数值非常接近,相变产生的整体宏观形状应变由平行于相界面的剪切应变和垂直于相界面的法向应变两部分组成.     

Ni70Co30/Cu磁性金属多层膜界面元素分布的X射线异常散射研究

应用X射线异常散射技术研究了[Ni₇₀Co₃₀(25A)/Cu(20A)]₂₀多层膜的界面结构, 结果表明, 退火前后Cu/Ni₇₀Co₃₀和Ni₇₀Co₃₀/Cu界面的温度行为不同.对于制备态样品, 界面结构是非对称的, 在Cu/Ni₇₀Co₃₀界面, 存在一个8A厚的CuNi₃过渡层和一个4A厚的NiCo层. 然而, Ni₇₀Co₃₀/Cu界面却不存在任何扩散. 285\textcelsius 2h退火后,Ni₇₀Co₃₀/Cu界面开始发生扩散, 产生了一个12A厚的CuNi₂Co过渡层. X射线能量分别在Co, Ni, Cu K吸收边附近的X射线漫散射实验, 揭示了在Ni₇₀Co₃₀/Cu多层膜的界面处, Cu与Ni和Co具有不同的横向关联长度, 显示了不均匀的横向分布.     

18 MeV质子辐照对TiNi形状记忆合金R相变的影响

 研究了用HZ-B串列加速器的18MeV质子辐照对TiNi形状记忆合金R相变的影响，辐照在奥氏体母相状态下进行。示差扫描量热法（DSC）表明，辐照后R相变开始温度T^s_R和逆马氏体相变结束温度T^f_A随辐照注量的增加而降低。当注量为1.53×10¹⁴/cm²时，T^sR和T^f_A分别下降6K和13K，辐照未引起R相变结束温度T^s_R和逆马氏体相变开始温度T^f_A的变化。表明辐照后母相(奥氏体相)稳定。透射电镜（TEM）分析表明辐照后没有引起合金可观察的微观组织变化。辐照对R相变开始温度T^s_{R和逆马氏体相变结束温度Af的影响可能是由于质子辐照后产生了孤立的缺陷团，形成了局部应力场，引起晶格有序度的下降所造成的。}     

Ni54Fe19Ga27单晶的形状记忆和超弹性

本文研究了单晶Ni₅₄Fe₁₉Ga₂₇不同方向的形状记忆效应、超弹性和磁性. 研究发现,单晶样品具有良好的双向形状记忆效应.不同晶体学方向的相变应变随着热循环次数的变化而改变. 在外应力作用下,通过应力诱发马氏体相变,样品在[001],[110],[111]方向分别产生了3.3%, 2% 和3%的可回复应变平台.磁性测量结果表明马氏体的磁晶各向异性能约为4.8× 10⁵ erg/cm³,远远小于变体孪生所需机械应力能,因此磁场的作用是使磁矩发生转动而不是使孪晶界移动, 成功揭示了不能在NiFeGa中获得大磁感生应变的物理根源.     

镍单晶膜上氧化镍的配位生长取向关系

对在膜面为(110),(001)和(111)的镍单晶膜上生成的氧化镍取向进行了电子衍射分析,除在(111)和(001)镍膜上肯定了前人已发现的氧化镍与镍的平行取向关系外,还在(110)和(001)镍单晶膜上发现了(111)_NiO∥(001)_Ni,〈110〉_NiO∥〈110〉_Ni取向关系以及〈110〉_NiO∥〈110〉_Ni氧化镍纤维织构。在所有氧化镍与镍的取向关系中均有〈110     

不同时效状态的含铜4%的铝合金在疲劳载荷下溶质原子与位错的交互作用

为了进一步研究在疲劳载荷下含铜4％的铝合金中的位错钉扎过程,进行了经过不同时效的试样的扭转疲劳试验,测定了经过各种应力循环数N以后的滞后迴线的形状和面积,从而算出了在每次循环中的能量消耗ΔE和最大抗扭矩T_m。所选择的时效温度和时效时间是使试样中分别有G.P.[1]区,G.P.[2]区,θ′相和稳定的θ相出现。把所得的ΔE-N曲线和T_m-N曲线的变化情况作比较时可以看出,在疲劳载荷的起始阶段引起位错钉扎的并不是由于相变产物如G.P.[1]或[2]区的作用。比较并分析了在各种时效状态下的第一周能量消耗值(ΔE)₁的变化,结果指出,在所研究的铝铜合金的情形,产生ΔE的原因是由于在位错附近的点阵中有起伏的内应力场出现,因为位错在这种内应力场中往复运动需要作功。产生这种起伏的应力场的因素有点缺陷(空位和溶质原子)、原子簇、G.P.[1]区和G.P.[2]区,或者其他种不在位错线上聚集或成核的缺陷。根据上述分析,可以认为,在疲劳载荷中,使位错钉扎的是由于溶质原子气团的形成。溶质原子在疲劳过程中通过空位的帮助进入位错,形成气团,使位错被钉扎。被钉扎的位错的动性减低,因而ΔE下降。在时效过程中,在位错线上成核的θ′和θ相,对于位错线也起着一定的钉扎作用。由上述的图象还可以推知,G.P.[1]区和G.P.[2]区不是在位错线上成核的,而θ′相和θ相则是在位错线上成核的。     

异构化能量分解分析Ni2CO5的(18，18)与(18，16)构型竞争

本文研究了中性Ni₂CO₅配合物的势能图,发现一个C_2v双桥羰基新构型,与以前报道的三羰基桥联的D_3h构型竞争Ni₂CO₅的基态结构. 尽管三桥式异构体拥有更有利的(18,18)电子构型,即双金属中心都满足18电子规则,中性的Ni₂CO₅$配合物更倾向于(18,16)电子结构的双桥式几何. 异构化能量分解分析表明,这样的结构优选是静电作用和轨道相互作用极大化的结果.     

Precipitation and fracture behaviour of Fe–Mn–Ni–Al alloys

The effects of Al addition on the precipitation and fracture behaviour of Fe–Mn–Ni alloys were investigated. With the increasing of Al concentration, the matrix and grain boundary precipitates changed from L1₀ θ-MnNi to B2 Ni₂MnAl phase, which is coherent and in cube-to-cube orientation relationship with the α′-matrix. Due to the suppression of the θ-MnNi precipitates at prior austenite grain boundaries (PAGBs), the fracture mode changed from intergranular to transgranular cleavage fracture. Further addition of Al resulted in the discontinuous growth of Ni₂MnAl precipitates in the alloy containing 4.2?wt.% Al and fracture occurred by void growth and coalescence, i.e. by ductile dimple rupture. The transition of the fracture behaviour of the Fe–Mn–Ni–Al alloys is discussed in relation to the conversion of the precipitates and their discontinuous precipitation behaviour at PAGBs.     

α- and β-Mn precipitates in the spinodal Fe30Ni20Mn25Al25 alloy

Precipitates in the spinodal alloy Fe₃₀Ni₂₀Mn₂₅Al₂₅, produced by drop-casting followed by hot extrusion, have been investigated using transmission electron microscopy. The as-extruded microstructure consisted of alternating, coherent body-centred cubic and B2 (ordered body-centred cubic) rods aligned along ?100? directions with a wavelength of ～60?nm. Upon annealing at 550°C, precipitates were formed having two distinct morphologies: relatively spherical precipitates with the α-Mn crystal structure and more elongated precipitates with the β-Mn crystal structure. Both precipitates existed simultaneously after annealing at this temperature for up to at least 99?h. The compositions of the precipitates and the orientation relationships between the precipitates and the spinodal matrix were determined.     

Effects of molybdenum on precipitation behaviours in aged cast stainless steels

The effects of Mo on precipitation behaviours in aged cast stainless steels have been investigated. Mo-free CF3 steel and Mo-bearing CF3M steel, both of which consisted of a duplex structure of ferrite and austenite phases, were prepared. Microstructural evolution in the ferrite phase during ageing at 723 K has been observed by transmission electron microscopy (TEM). Precipitates in CF3 steel were identified to belong to the G-phase and possess lattice coherency with the ferrite phase at interphase boundaries. On the other hand, precipitates in CF3M steel were found to be nanodomains of not only to the G-phase but also to another phase enriched in Mo. Some of the nanodomains containing Mo exhibited diffraction patterns having pseudo five-fold symmetry, but others exhibited regular periodicity in high-resolution TEM images. The atomic structure of the Mo-related nanodomains is proposed to be a distorted χ-phase that retains coherency with the matrix.     

Characterization of core-shell nanoparticles by small angle neutron scattering

The Ni₃Si-type nanoparticles dispersed in a mixture of H₂O/D₂O were characterised by SANS using the contrast variation method. The existence of a core-shell structure in the nanoparticles with a Ni₃Si(Al) core and amorphous SiO_x shell is confirmed by the SANS measurements. The nanoparticles were produced by extracting precipitates from a bulk Ni-13.3Si-2Al ( at. %) alloy using electrochemical phase separation technique and were pre-characterised by X-ray diffraction and transmission electron microscopy. By comparing the precipitate morphology in the Ni-Si-Al alloy with the extracted nanoparticles in the SANS measurements, it is clearly established that the precipitates shape and size are unaffected by the extraction process and that the amorphous shell forms on top of the particle core. However, the present measurement could not confirm or exclude the presence of H atoms in the shell structure. PACS 61.12.Ex; 61.12.-q; 61.46.Df; 61.82.Rx     

周期性多层膜合金化制取的TiNi形状记忆薄膜的室温微结构特征

用掠入射X射线衍射及X射线反射对磁控溅射制取的等原子比Ni／Ti周期性多层膜晶化热处理 后的TiNi形状记忆薄膜室温微结构进行了研究.TiNi形状记忆薄膜在深度方向的相分布和元 素分布是不均匀的，都是一种多层结构.室温下其微结构特征为最外层是Ti氧化膜，再下层 是Ti₃Ni₄,B19’马氏体相和少量的B2奥氏体相的三相混合物，靠近 基体为主要相成分马氏体，最后是Ni和Si界面反应层.X射线反射率的拟和结果显示薄膜微结 构的分析是合理的.薄膜中相深度分布的不均匀性主要是动力学因素决定的. 关键词： 相深度分布 形状记忆 TiNi 多层膜     

Impedance and electron diffraction studies on single crystals of BINIVOX

Single crystals of the nominal composition Bi₂V_0.9Ni_0.1O_5.35 were prepared. They were studied by TGA/DTA, impedance spectroscopy and electron diffraction. The impedance of the crystals with Pt electrodes was measured in two directions: parallel and perpendicular to the layers of the intergrowth structure in the frequency range 10⁻²−10⁷ Hz at temperatures between 300 and 940 K. Arrhenius type plots for both directions show two linear regions with different activation energies. In the low temperature region the conductivity in the direction parallel to the layers was by a factor of about 1000 larger than in the perpendicular direction. In the high temperature region the ratio of conductivities was about 100. A time dependence of the conductivity in the perpendicular direction was observed during heating and cooling in limited temperature ranges. The electron diffraction experiments gave evidence that the superlattice spots present in the diffraction patterns at low temperature, disappear reversibly at temperatures higher than 650 K. The transition temperatures observed in the DTA and in the electron diffraction experiments correspond to the temperature of changes of the activation energy. An order-disorder transition of oxygen ions is considered to be responsible for this phenomenon. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998.     

Characterization of aging-induced microstructural changes in M250 maraging steel using magnetic parameters

The best combinations of mechanical properties (yield stress and fracture toughness) of M250 maraging steel is obtained through short-term thermal aging (3–10 h) at 755 K. This is attributed to the microstructure containing precipitation of intermetallic phases in austenite-free low-carbon martensite matrix. Over-aged microstructure, containing reverted austenite degrades the mechanical properties drastically. Hence, it necessitates identification of a suitable non-destructive evaluation (NDE) technique for detecting any reverted austenite unambiguously during aging. The influence of aging on microstructure, room temperature hardness and non-destructive magnetic parameters such as coercivity (H_c), saturation magnetization (M_s) and magnetic Barkhausen emission (MBE) RMS peak voltage is studied in order to derive correlations between these parameters in aged M250 maraging steel. Hardness was found to increase with precipitation of intermetallics during initial aging and decrease at longer durations due to austenite reversion. Among the different magnetic parameters studied, MBE RMS peak voltage was found to be very sensitive to austenite reversion (non-magnetic phase) as they decreased drastically up on initiation of austenite reversion. Hence, this parameter can be effectively utilized to detect and quantify the reverted austenite in maraging steel specimen. The present study clearly indicates that the combination of MBE RMS peak voltage and hardness can be used for unambiguous characterization of microstructural features of technological and practical importance (3–10 h of aging duration at 755 K) in M250 grade maraging steel.     

Phase transformation in Ni–Mn–Sn ferromagnetic shape memory alloy thin films induced by dense ionization

The effects of 200 MeV Au ions irradiation on the structural and magnetic properties of Ni–Mn–Sn ferromagnetic shape memory alloy (FSMA) thin films have been systematically investigated. In order to understand the role of initial microstructure and phase of the film with respect to high energy irradiation, the two types of Ni–Mn–Sn FSMA films having different phases at room temperature were irradiated, one in martensite phase (Ni_58.9Mn_28.0Sn_13.1) and other in austenite phase (Ni₅₀Mn_35.6Sn_14.4). Transmission electron microscope (TEM) and scanning electron microscope (SEM) images along with the diffraction patterns of X-rays and electrons confirm that martensite phase transforms to austenite phase at a fluence of 6×10¹² ions/cm² and a complete amorphization occurs at a fluence of 3×10¹³ ions/cm², whereas ion irradiation has a minimal effect on the austenitic structure (Ni₅₀Mn_35.6Sn_14.4). Thermo-magnetic measurements also support the above mentioned behaviour of Ni–Mn–Sn FSMA films with increasing fluence of 200 MeV Au ions. The results are explained on the basis of thermal spike model considering the core and halo regions of ion tracks in FSMA materials.     

In situ synchrotron X‐ray diffraction analysis of deformation behaviour in Ti–Ni‐based thin films

Deformation mechanisms of as‐deposited and post‐annealed Ti_50.2Ni_49.6, Ti_50.3Ni_46.2Cu_3.5 and Ti_48.5Ni_40.8Cu_7.5 thin films were investigated using the in situ synchrotron X‐ray diffraction technique. Results showed that initial crystalline phases determined the deformation mechanisms of all the films during tensile loading. For the films dominated by monoclinic martensites (B19′), tensile stress induced the detwinning of 〈011〉 type‐II twins and resulted in the preferred orientations of (002)_B19′ parallel to the loading direction (∥ LD) and (020)_B19′ perpendicular to the LD (⊥ LD). For the films dominated by austenite (B2), the austenite directly transformed into martensitic variants (B19′) with preferred orientations of (002)_B19′ ∥ LD and (020)_B19′ ⊥ LD. For the Ti_50.3Ni_46.2Cu_3.5 and Ti_48.1Ni_40.8Cu_7.5 films, martensitic transformation temperatures decreased apparently after post‐annealing because of the large thermal stress generated in the films due to the large differences in thermal expansion coefficients between the film and substrate.     

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.