亚稳态FeCu固溶体微粉原子相互作用势的计算

本文介绍了亚稳态Fe50Cu50固溶体晶格常数的测量结果,应用金属结构的经典概念并考虑到原子核周围电子密度的高斯型球对称分布,导出了计算金属中一个原子的平均内能和两种不同金属原子相互作用势的普遍公式.对亚稳态Fe50Cu50合金原子相互作用势作计算,得到平衡时fcc-FeCu的晶格常数为0.36433 nm与实验测量结果接近,也与H.R.Gong等人对亚稳态FeCu合金的研究结论一致,证实了亚稳态Fe50Cu50合金是以fcc结构形式存在的固溶体.     

Half-Heusler合金NiFeSb和NiMnSb的磁性及电子结构的第一性原理研究

用基于密度泛函理论的第一性原理方法,计算了half-Heusler合金NiFeSb和NiMnSb的晶体结构、磁性及电子结构。计算结果表明,磁性原子Fe和Mn在两种合金的总磁矩中贡献最大,在NiFeSb总磁矩中,Ni原子贡献比例接近在NiMnSb中的2倍,而Sb原子的贡献比例是在NiMnSb中的1/5;两种合金的自旋向上能带都具有明显的金属特征,而自旋向下能带有明显的差别;两种合金费米能级以下的总态密度(DOS)主要由Ni-3d 和Fe-3d（Mn-3d）态决定,费米能级以上主要由Fe-3d（Mn-3d）自旋向下部分决定。     

热处理过程对Cr75(Fe0.67Mn0.33)25合金磁性的影响

利用M?ssbauer谱和磁测量方法对经过适当热处理的Cr₇₅(Fe_0.67Mn_0.33)₂₅合金的磁性进行了研究．结果表明合金中原子的化学分布对合金的磁有序状态的形成起重要作用．通过热处理过程影响合金中的富Cr、富Fe原子集团，引起反铁磁、铁磁转变温度的升高．合金中的富Cr、富Fe原子集团导致合金中的磁相分离 关键词：     

合金元素韧化或脆化FeAl金属间化合物的微观机制

通过测量二元FeAl以及含B，Zr或Si的FeAl合金的正电子寿命谱参数，计算合金基体和缺陷处的价电子密度.结果表明，当Al原子和Fe原子结合形成FeAl合金时，Al原子提供价电子与Fe原子的3d电子形成局域的共价键.FeAl合金基体的价电子密度很低，FeAl合金中金属键和共价键共存.FeAl合金晶界缺陷的开空间大于Fe空位或Al空位的开空间，FeAl合金晶界处的金属键合力很弱.在FeAl合金中加入少量的B，一部分B原子以间隙方式固溶到FeAl基体中，增加基体的价电子密度；另一部分B原子偏聚到FeAl合金的晶界上，也增加了晶界处的价电子密度.在FeAl合金中加入Zr，增加了合金中的金属键成分，使基体中的价电子密度增加，增强了基体中金属键合力.Zr原子的加入还降低了FeAl合金的有序度，使合金晶界容易弛豫，晶界缺陷的开空间变小.Zr原子在晶界附近出现，还增加了晶界处的价电子密度.在FeAl中加入B或Zr有利于提高合金的韧性.在FeAl合金中加入Si，晶界处的Si原子与邻近的原子形成强的共价键，使得在晶界处参与形成金属键的价电子密度降低.在FeAl中加入Si使合金更脆. 关键词：     

非晶态铁磁Fe-Ni基合金的穆斯堡尔谱研究

本文研究了非晶态合金Fe_81-xNi_xSi_3.5B_13.5C₂(x=5,10,15,20,25,30,35)及坡莫合金Fe₅₀Ni₅₀在室温和外加磁场下的穆斯堡尔谱,用拟谱方法获得了超精细相互作用的参量及超精细场分布P(H).实验结果表明,非晶态Fe-Ni基合金存在两种磁性铁原子且有类因瓦特性,在x=15左右存在异常现象.文中提出了外加磁场和低温的外界条 关键词：     

非晶态铁磁Fe—Ni基合金的穆斯堡尔谱研究

本文研究了非晶态合金Fe_(81-x)Ni_xSi_(3.5)B_(13.5)C_2(x=5,10,15,20,25,30,35)及坡莫合金Fe_(50)Ni_(50)在室温和外加磁场下的穆斯堡尔谱,用拟谱方法获得了超精细相互作用的参量及超精细场分布P(H).实验结果表明,非晶态Fe-Ni基合金存在两种磁性铁原子且有类因瓦特性,在x=15左右存在异常现象.文中提出了外加磁场和低温的外界条件,就磁有序而言,具有相似的效应.同时,用类金属的键合作用和金属原子的转移效应较好地解释了非晶态过渡金属(TM)-类金属(M)合金的实验现象.     

XAFS和XRD研究高能球磨对Fe70Cu30合金结构的影响

利用XRD和XAFS方法研究机械合金化Fe70Cu30二元金属合金随球磨时间的结构变化.XRD结果表明,球磨2 h后,部分金属Fe与Cu生成Fe-Cu合金;球磨20h后,金属Fe与Cu已完全合金化生成Fe-Cu合金,并只在2θ=44°处出现一个宽化的弱衍射峰,认为是在球磨20h后的Fe70Cu30合金中共存着fcc和bcc结构的Fe-Cu合金相.XAFS结果进一步表明,在球磨的初始阶段(2h),fcc结构的Cu颗粒的晶格产生较大的畸变,其无序度σ(σ＝σT+σS)为0.0190nm.球磨5h后,部分fcc结构的Cu原子进入了无序度相对较小的bcc结构的α-Fe相,导致Cu原子的平均无序度σ降为0.0108 nm.球磨10h后,样品中很大比例的Fe原子处于fcc结构的Fe-Cu合金相,其无序度为σ=0.0119 nm;而大部分Cu原子依然保持fcc结构,无序度为σ=0.0110 nm.这是由于扩散到bcc结构α-Fe相的Cu原子超过某一浓度后(约30%-40%),Cu原子能诱导其产生fcc结构相变所致.球磨时间增加到20h,样品中Cu原子和Fe原子在fcc和bcc相的比例与球磨10h基本相同,生成的Fe-Cu合金混合相的组成和结构分别近似于bcc结构的Fe80Cu20和fcc结构的Fe60Cu40.     

硫原子在镍基合金825(001)面吸附的第一性原理研究

元素硫在镍基合金表面吸附产生严重的电化学腐蚀,为从原子尺度研究硫腐蚀机理,采用第一性原理方法,构建并优化了镍基合金825的晶胞结构模型,计算分析了S原子在镍基合金825耐蚀性较差面(001)晶面的吸附及电子转移情况.结果表明:Ni原子占据顶角, Cr原子和Fe原子对称占据面心是镍基合金825稳定的晶胞结构;原子S在镍基合金825(001)面上最稳定的吸附位为四重穴位,吸附能为-6.51 eV; S吸附前后的态密度(DOS)和二维电荷差分密度图(DCD)对比发现,镍基合金825中Fe与S之间电荷偏移明显,形成离子键,易生成腐蚀产物Fe_xS_y. S的吸附对镍基合金825中Cr原子的电子分布影响不大,且合金中Cr和Ni抑制了合金中Fe与S之间的相互作用,从而提高了合金耐蚀性.     

Fe_50Cu_50合金熔体相分离过程的分子动力学模拟

基于镶嵌原子势,采用分子动力学模拟的方法探讨了Fe50Cu50合金熔体在1823 K下液-液相分离过程.结果发现:熔体中同类原子配位数随弛豫时间的延长逐渐增大,而异类原子配位数逐渐减少;由BhatiaThornton结构因子SCC(q)获得的相关长度随时间的变化也呈现出明显的递增趋势,表明该合金熔体在该温度下发生了液—液相分离.原子轨迹的可视化显示结果发现,相分离的初期,体系呈明显的网络状组织,随时间的延长,异类原子逐渐分离,最终形成富Fe和富Cu的相分离组织,符合调幅分解特征.与Fe75Cu25合金熔体的相分离过程对比发现,Fe与Cu原子数目相差越小,相分离行为越剧烈,形成稳定分层结构所需的时间越短.以上研究从原子尺度上表征了金属熔体的相分离过程.     

机械合金化Fe100-xCux体系的X射线吸收精细结构研究

利用X射线吸收精细结构(XAFS)方法研究机械合金化制备的Fe_100-xCu_x(x=0,10,20,40,60,70,80,100,x为原子百分比)合金中Fe和Cu原子的局域环境结构.对于Fe_100-xCu_x(x≥40)二元混合物,球磨160h后,Fe原子的近邻配位结构从bcc转变为fcc,但Cu原子的近邻结构保持其fcc不变.与之相反,在Fe₈₀Cu₂₀和Fe₉₀Cu₁₀(x≤20)合金中,Fe原子的近邻配位保持其bcc结构而Cu原子的近邻配位结构从fcc转变为bcc结构.XAFS结果还表明,fcc结构的Fe_100-xCu_x样品中Fe的无序因子σ(0.0099nm)比bcc结构的Fe_100-xCu_x中的σ(0.0081nm)大得多;并且在机械合金化Fe_100-xCu_x(x≥40)样品中Fe原子的σ(0.0099nm)比其Cu原子的σ(0.0089nm)大.这表明机械合金化Fe_100-xCu_x样品中Fe和Cu原子可以有相同的局域结构环境但不是均匀的过饱和固溶体,而是由Fe富集区和Cu富集区组成的合金.我们提出互扩散和诱导相变机理来解释在球磨过程中Fe_100-xCu_x合金产生从bcc到fcc和从fcc到bcc变化的结构相变 关键词： XAFS 100-xCu_x合金')" href="#">Fe_100-xCu_x合金 机械合金化     

Invar effect by local moment model

On the basis of the molecular field approximation the magnetic part of the thermal expansion coefficient of fcc Fe-Ni alloys is evaluated. The main possibility of explaining the invar effect is shown and its physical matter is revealed. The invar phenomenon is caused by mixed exchange interaction and by strong dependence of the exchange interaction J_FeFe on the interatomic distance. The latter circumstance gives rise to a large spontansous magnetostriction which compensates the normal thermal expansion of these alloys.     

Mössbauer study of Slovak meteorites

⁵⁷Fe Mössbauer spectroscopy was used as an analytical tool in the investigation of iron containing compounds of two meteorites (Rumanová and Ko?ice) out of total of six which had fallen on Slovak territory. In the magnetic fraction of the iron bearing compounds in the Rumanová meteorite, maghemite, troilite and Fe-Ni alloy were identified. In the non-magnetic fraction silicate phases were found, such as olivine and pyroxene. The paramagnetic component containing Fe^3?+? ions corresponds probably to small superparamagnetic particles. The Ko?ice meteorite was found near the town of Ko?ice in February 2010. Its magnetic fraction consists of a Fe-Ni alloy with the Mössbauer parameters of the magnetic field corresponding to kamacite α-Fe(Ni, Co) and troilite. The non-magnetic part consists of Fe^2?+? phases such as olivine and pyroxene and traces of a Fe^3?+? phase. The main difference between these meteorites is their iron oxide content. These kinds of analyses can bring important knowledge about phases and compounds formed in extraterrestrial conditions, which have other features than their terrestrial analogues.     

Mössbauer and magnetization measurements on two ferromagnetic alloys containing 119Sn

¹¹⁹Sn Mössbauer effect and magnetization measurements have been performned at temperatures between 4.2 and 700°K on an invar alloy (35.8 at.% NiFe) and ordered FeCo containing tin. The Mössbauer results are shown to be consistent with a model in which interionic separation is important to the hyperfine interaction. The magnetization measurements on the invar alloy reflect its sensitive magnetic properties.     

Role of the chemical ordering on the magnetic properties of Fe–Ni cluster alloys

The spin and orbital moments of fcc Fe-Ni cluster alloys are determined within the framework of a d-band Hamiltonian including the spin-orbit coupling non perturbatively. Different sizes (up to 321 atoms), compositions, and chemical configurations (random alloys as well as core-shell arrays of iron and nickel atoms) are considered in order to reveal the crucial role played by local order and stoichiometry on the magnetic moments of the clusters. Interestingly, we have found considerably reduced average magnetizations for Fe-Ni clusters with Fe cores compared to that of the bulk alloy with the same composition. Indeed, in these configurations not only antiparallel arrangements between the local moments of some Fe atoms within the iron core are found, but also the total magnetization of the surface Ni atoms is significantly quenched. On the opposite, the disordered and Ni-core cluster alloys are characterized by high magnetizations resulting from saturated-like contributions from both Ni and Fe atoms, in agreement with recent ab-initio calculations. In general, the local orbital magnetic moments are strongly enhanced with respect to their bulk values. Finally, the variation of the orbital-to-spin moment ratio with the chemical order is discussed.     

Electron irradiation effects on iron-nickel invar alloys

Electron irradiation was used as a means of accelerating the diffusion in Fe-Ni alloys. Mössbauer effect, X-ray and electron microscopy experiments on samples with 28 to 50% Ni show that the Invar character disappears after irradiation up to 250°C, in particular the variation of the lattice parameter versus temperature becomes linear around room temperature. At the same time, two phases appear in the alloy, one rich in nickel and ordered with FeNi (AuCu) superstructure, the other rich in iron and probably ordered (Fe₃Ni). The Invar state is therefore shown to be a metastable state. A diagram of the Fe-Ni alloy is proposed.     

A model of magnetic inhomogeneous structure for Fe-Ni invar alloys

The magnetic inhomogeneous structure revealed by neutron small angle scattering for Fe-Ni Invar alloys can be interpreted in terms of a model in which an effective local concentration of Fe for each atom within a sphere is taken into account in order to determine the magnetic moment of the atom.     

Magnetic structure of critical Fe-Ni alloys as derived from Arrott plots and Mössbauer spectra

New evidence of magnetic phase transition brought about by an external magnetic field acting on critical composition bulk Fe-Ni alloys was found by using iron-nickel alloys containing 30 wt% Ni and 31.3 wt% Ni, respectively (balance Fe). The split in the central peak of Mössbauer spectrum of the Fe-Ni alloy containing 29.7 wt% Ni, at its Curie temperature in a weak external magnetic field of 3100 Oe, is a conclusive evidence of its superparamagnetic structure.     

Invar effect in iron based fcc alloys

A model of interacting virtual bound states is used to calculate the atomic magnetic moments in iron based fcc alloys. This clearly shows that the magnetic moment not only depends on environment but on magnetic order too. Consequently there is a change in magnetic moment between 0 K and the ordering temperature which leads to a change in cohesive energy. If the iron–iron exchange coupling constant is negative the Invar effect arises from iron atoms surrounded by iron atoms whose magnetic moments are parallel to this of the central atom.     

Absence of magnetism in hcp iron-nickel at 11 K

Synchrotron M?ssbauer spectroscopy (SMS) was performed on an hcp-phase alloy of composition Fe92Ni8 at a pressure of 21 GPa and a temperature of 11 K. Density functional theoretical calculations predict antiferromagnetism in both hcp Fe and hcp Fe-Ni. For hcp Fe, these calculations predict no hyperfine magnetic field, consistent with previous experiments. For hcp Fe-Ni, however, substantial hyperfine magnetic fields are predicted, but these were not observed in the SMS spectra. Two possible explanations are suggested. First, small but significant errors in the generalized gradient approximation density functional may lead to an erroneous prediction of magnetic order or of erroneous hyperfine magnetic fields in antiferromagnetic hcp Fe-Ni. Alternately, quantum fluctuations with periods much shorter than the lifetime of the nuclear excited state would prohibit the detection of moments by SMS.     

Mössbauer spectroscopic study of meteorites recovered on Antarctica

The chemical states of iron in sixteen Antarctic meteorites belonging to H-group chondrites were studied by means of Mössbauer spectroscopy. An Fe-Ni alloy, troilite, paramagnetic Fe(III), and two kinds of paramagnetic Fe(II) were observed in each meteorite. The Mössbauer parameters indicated that the Fe(II) components can be assigned to olivine and some pyroxenes. The relative area intensities of Fe(III) in the chondrites correlated positively with iodine content, which was determined by radiochemical neutron activation analysis, and those of two Fe(II)-species correlated negatively with the content. On the basis of the data on the halogen and the Mössbauer spectrocopy, the terrestrial contamination on Antarctic meteorites is discussed.