基于特殊准随机结构模型的FCC Fe-Cu无序固溶体合金的弹性稳定性

采用基于投影缀加波赝势和广义梯度近似的第一性原理计算方法计算FCC结构Fe以及3种Fe-Cu无序固溶体合金(Cu原子摩尔分数分别为25%、37.5%和50%)的基态性质、弹性常数以及电子结构,其中Fe-Cu无序固溶体合金采用特殊准随机结构模型进行计算。能量计算结果表明:FCC结构Fe存在无磁、低铁磁以及高铁磁性3种状态,而FCC结构Fe-Cu无序固溶体合金只存在无磁与高铁磁性两种状态。高铁磁性FCC结构Fe不满足Born弹性稳定性准则,铁磁性FCC结构Fe-Cu无序固溶体合金的弹性稳定性随着Cu含量的增加而增加;当Cu原子的摩尔分数不低于37.5%时,Fe-Cu无序固溶体合金满足Born弹性稳定性准则,此时合金以亚稳态形式存在。     

钕铁硼用磁温度补偿合金的成分

通过电弧炉制备了磁温度补偿合金,利用振动样品磁强计(VSM)测试了其热磁性能,并采用X射线衍射(XRD)分析其相结构,对Fe-Ni二元合金及三元合金进行了系统的研究.结果表明对于Fe-x%Ni二元合金,当31≤x≤33时,合金由γ面心和α体心立方结构组成,当x=36时,合金为γ单相结构;Mo、Mn、Si、Al、Cr等元素降低了Fe-Ni合金的居里温度、饱和磁化强度,Cu、Co、C元素提高了Fe-Ni合金的居里温度、饱和磁化强度;元素C和Mo能显著地改变合金的居里温度、饱和磁化强度,提高合金的△B/△t最大值,有利于合金磁性能的调控.     

Direct Electrodeposition of Fe-Ni Alloy Films on Silicon Substrate

在n-型Si片(100)面上直接电沉积Fe-Ni合金薄膜,并对电沉积过程特征及薄膜的结构和性能进行了研究。当阴极电流密度高于1.0 A/dm2时,可获得连续致密的合金薄膜,且电沉积表现为异常共沉积过程。在1.0~4.0 A/dm2范围内改变电流密度可调控合金薄膜的Ni质量分数从45%到78%之间改变,对应的电流效率在60%到66%之间变动。从XRD和TEM结果来看,合金薄膜由尺寸为10~30nm的纳米晶粒组成,且表现为Fe-Ni面心立方固溶体结构。合金薄膜的磁滞回线表现出较高的饱和磁化强度和接近于零的矫顽力,表明该种纳米合金薄膜具有很好的软磁性能。     

合金元素镍对FCC Fe-Cu析出相结构稳定性的影响

采用基于投影缀加波赝势和广义梯度近似的第一性原理和特殊准随机结构模型计算FCC结构Fe-25Cu、Fe-31.25Cu、Fe-3.125Ni-25Cu和Fe-3.125Ni-31.25Cu无序固溶体的基态性质、弹性常数以及电子结构,其中无序固溶体晶胞结构建立在由特殊准随机结构方法所产生的结构模型基础上。计算结果表明：FCC 结构Fe-Ni-Cu无序固溶体存在无磁性与铁磁性两种状态,其中铁磁性 Fe-Cu 和 Fe-Ni-Cu 无序固溶体的能量相对较低;铁磁性Fe-25Cu和Fe-3.125Ni-25Cu无序固溶体不满足Born弹性稳定性准则,而Fe-31.25Cu和Fe-3.125Ni-31.25Cu无序固溶体满足Born弹性稳定性准则,以亚稳态形式存在,合金元素Ni的加入显著提高了铁磁性FCC结构Fe-31.25Cu无序固溶体的结构稳定性。     

Al-Cu-Cr系准晶及其类似相的形成规律

本文为了探明Al-Cu-Cr系准晶及其类似相的形成规律，以指导Al-Cu-Cr系准晶合金设计。通过分析研究用热压法制备的Al-Cu-Cr准晶与纯铝的复合材料中不同条件下形成的各个Al-Cu-Cr相的成分和结构，绘制了Al-Cu-Cr三元成份．结构相图，结果表明相图中存在两条等电子浓度线，一条是二十面体准晶及其类似相的等电子浓度线，电子浓度e／a=1．86：另一条是十次准晶及其类似相的等电子浓度线，电子浓度e／a=2．09。这充分证实了准晶及其类似相是电子相，服从Hume—Rothery规则。     

MAGNETIC PROPERLIES AND STRUCTURE OF A MIXTURE OF α-Fe and Fe_3N DURING MECHANICAL ALLOYING PROCESS

利用X射线衍射研究了α-Fe与Fe3混合粉末机械合金化过程中结构的变化．并测量了球磨不同时间后其饱和磁化强度的变化结果表明,随着球磨时间的延长,Fe3N相迅速分解直至消失,N原子部分固溶于α-Fe中,24h后可形成稳定的α-Fe（N）过饱和固溶体,其中N的质量分数约为0．290％-0．346％．随着球磨时间的延长,α-Fe的晶粒尺寸逐渐减小,24h后趋于定值,约为8nm．球磨引起样品中Fe原子周围N原子位置的变化,使得球磨过程中混合粉末的饱和磁化强度开始时降低,5h后又有所增加,24h后达到一定值     

Nd(Fe1-xCox)10V2的Mossbauer谱

通过X射线衍射、磁测量和Mossbauer谱等测试方法研究了Nd(Fe1-xCox)10V2的结构和磁性.结果表明:Nd(Fe1-xCox)10V2(x=0,0.05,0.1,0.15,0.2)化合物的晶体结构均为ThMn12型结构;随着Co含量增大,晶格常数将单调减少,居里温度Tc呈单调增大,饱和磁化强度Ms逐渐增加.Co部分取代Nd(Fe1-xCox)10V2中的Fe原子,将择优占据8i铁晶位.     

离子束溅射制备Co／Pt多层膜的磁性研究

室温下采用ＶＳＭ测定了离子束溅射（ＩＢＳＤ）技术制备的Ｃｏ／Ｐｔ多层膜垂直方向的Ｍ－Ｈ回线。研究结果表明：Ｃｏ／Ｐｔ多层膜中单位体积Ｃｏ的饱和磁化强度ＭｓＣｏ小于块状Ｃｏ的饱和磁化强度;Ｃｏ／Ｐｔ多层膜的饱和磁化强度（Ｍｓ）与厚度有关：随Ｃｏ层厚度ｔＰｔ和多层膜总厚度ｔｆ的增加而增大,随Ｐｔ层厚度ｔｐｔ的增加而减小;外推结果表明当ｔＣｏ小于一个原子层厚（≈０２５ｎｍ）时,室温下Ｃｏ／Ｐｔ多层膜的饱和磁化强度为零,呈顺磁性     

304不锈钢板材制备过程中的磁性变化及其控制

研究了奥氏体不锈钢板 (0Cr18Ni9)在加工制备过程中的磁性变化规律。结果表明,合金的饱和磁化强度Ms与材料中磁性相含量有关。铸态合金存在残存的高温铁素体相而呈现一定磁性,饱和磁化强度Ms达35.8 kA/m。随着加工进行,主要是经历各道加热工序时,合金的Ms逐渐减弱。最终固溶态下合金的Ms已经降低为1.4 kA/m。锻态合金在单相奥氏体温度区内的退火处理可以有效减少合金中残存的高温铁素体并使饱和磁化强度降低,可作为控制磁性的有效措施。     

高压下Fe84Nb4W3B9纳米晶软磁块体合金的制备

采用机械合金化(MA)法和低温高压快速烧结工艺制备了Fe84Nb4W3B9软磁合金粉末及其块体合金,并研究了粉末的晶粒尺寸、热稳定性和块体合金的相组成,晶粒大小以及相对密度与烧结条件的关系.结果表明(1)MA60h后,可获得单相α-Fe纳米晶(8.6nm)过饱和固溶体粉末(2)在MA粉末DSC升温曲线中,分别出现3个强弱不一的放热峰,依次发生了畸变的纳米晶过饱和固溶体的结构弛豫、纳米晶粒长大以及固溶体的相分解过程;(3)在P=5.5GPa,t=3min的烧结条件下,当Pw≥980W后,可获得相对密度98.2%以上、单相α-Fe纳米晶(20.3nm)块体合金,其磁性能为比饱和磁化强度Ms=154.0emu·g-1,矫顽力Hc=7.474×103A·m-1.     

High-entropy alloys: Interrelations between electron concentration,phase composition,lattice parameter,and properties

An analysis of more than 200 high-entropy alloys (HEA) allowed us to find interrelations between the electron concentration, phase composition, lattice parameter, and properties of solid solutions with bcc and fcc crystal lattices. Main conditions for the appearance of high-entropy chemical compounds, such as Laves, σ, and μ phases were determined. The necessary condition for the formation of 100% high-entropy σ phase is the formation of σ phase in two-component alloys for different combinations of elements, which are components of the HEA, and the electron concentration should be 6.7–7.3 electrons per atom. To form a 100% high-entropy Laves phase, the following conditions should be fulfilled: the total negative enthalpy of mixing of alloy is about –7 kJ/mol and less; the difference between the atom sizes in a pair is more than 12%; the enthalpy of the mixing of two present elements is less than –30 kJ/mol; and the average electron concentration is 6–7 electrons per atom. It was shown that the ratios of lattice parameters of solid-solution HEA, which were experimentally determined, to the lattice parameter of the most refractory metal in the HEA determine the value of the modulus of elasticity.     

Composition and non-equilibrium crystallization in partially devitrified co-rich soft magnetic nanocomposite alloys

The body-centered cubic (bcc) phase tends to preferentially nucleate during solidification of highly undercooled liquid droplets of binary alloy systems, including Fe–Co, Fe–Ni and Fe–Cr–Ni. We investigate a similar tendency during the partial devitrification of Co-rich amorphous precursors of composition (Co_1?xFe_x)₈₈Zr₇B₄Cu₁ by identifying the structure and composition of the nanocrystalline grains. The Co:Fe ratio of the bcc nanocrystals varies linearly with the Co:Fe ratio of the amorphous precursor, and can lie well within the single-phase face-centered cubic (fcc) region of the Fe–Co phase diagram at the crystallization temperature. Classical nucleation theory therefore suggests several potential explanations for the preferential nucleation of bcc phase from an amorphous precursor, including: (i) a reduced amorphous/bcc interface energy as compared to the close-packed phases; (ii) a lower strain of precipitation for bcc nuclei as compared to close-packed fcc and hexagonal close-packed nuclei; and (iii) stabilization of the bcc phase by dissolved glass-formers such as Zr and B.     

Fe基合金连续冷却相变的分子动力学模拟

采用分子动力学模拟了Fe99Cu1合金在1×1014 K/s冷速下从fcc奥氏体结构转变为bcc铁素体结构的相变过程.结果表明,Fe99 Cu1合金在900～800℃之间开始发生相变,600 ℃时相变明显,100℃时55％的原子转变为bcc结构.Cu元素阻碍合金相变,并且促进bcc孪晶形成.     

Formation and chemical leaching effects of nonequilibrium Al0.6(Fe25Cu75) alloy powder produced by rod milling

The formation and chemical leaching effects of a nonequilibrium Al_0.6(Fe₂₅Cu₇₅)_0.4 powder produced by rod milling is described. X-ray diffraction, transmission electron microscopy, differential scanning calorimetry and vibrating sample magnetometry were used to characterize both the as-milled and leached specimens. After 400 h of milling, only the bcc AlFe phase with an amorphous phase was detected in the XRD patterns. The crystallite size for the bcc AlFe phase (110) after 400 h of milling was about 5.3 nm. The peak temperature and the crystallization temperature of the as-milled powders were 448.7 and 428.0 °C, respectively. Al atoms leaching from the as-milled bcc AlFe powders in the L1 condition did not alter the diffraction pattern significantly, even though Al atoms had been removed. After the L1 specimen was annealed at 500 °C for 1 h, the bcc AlFe phase transformed to the fcc Cu, Fe, and CuFe₂O₄ phases. The peak widths of L1 and L2 specimens were similar, but became broader than that of the as-milled powder. The saturation magnetization decreased with increasing milling time, and a value of 10.4 emu/g was reached after 400 h of milling. After cooling the specimen from 750 °C, the magnetization slowly increased at approximately 491.4 °C, indicating that the bcc AlFe phase had transformed to the fcc Cu and Fe phases.     

放电等离子烧结双相AlCrCoFeNi2.1 高熵合金的微观组织、耐腐蚀性能和力学性能

采用放电等离子烧结法在不同温度下制备AlCrCoFeNi_2.1高熵合金（HEA）,并对其微观组织、耐腐蚀性能和力学性能进行了研究。结果表明,烧结后的AlCrCoFeNi_2.1 HEA最大相对密度可达99.18%;该HEA主要由体心立方（bcc）相和面心立方（fcc）相组成,其比例分别为20.6%和79.4%。与fcc相相比,AlCrCoFeNi_2.1 HEA中bcc相的再结晶组织和变形组织更多,且bcc相在3.5%（质量分数）NaCl溶液中更容易被腐蚀。随着应变速率的增加,bcc相和fcc相的压力恢复速率降低,硬化效果增强。在1050 ℃下烧结的AlCrCoFeNi_2.1 HEA具有较高的极限抗拉伸强度,这主要归因于晶界强化、固溶强化和合金粒子之间良好的界面结合。该HEA的断裂形式包括bcc相的脆性断裂和fcc相的韧性断裂。     

Cr对CoFeNiAl0.6Ti0.4的合金化行为与组织的影响

采用"机械合金化+SPS烧结"制备了CoFeNiAl0.6Ti0.4和CrCoFeNiAl0.6Ti0.4块体高熵合金,研究元素Cr对CoFeNiAl0.6Ti0.4高熵合金的合金化行为和组织的影响。结果表明:Cr元素并不影响CoFeNiAl0.6Ti0.4高熵合金的合金化顺序,而影响完全合金化后的晶体结构,使CoFeNiAl0.6Ti0.4高熵合金原本单一的fcc结构转变为fcc+bcc结构。SPS烧结后,CoFeNiAl0.6Ti0.4高熵合金主要为fcc+bcc主相+微量bcc白相,而Cr元素的添加促使合金转变成fcc主相+微量bcc白相。同时,合金元素Cr的加入,使CoFeNiAl0.6Ti0.4高熵合金中的微量白相,由原本富Al和Fe元素转变为富Al和Ti元素;且Cr元素不影响CoFeNiAl0.6Ti0.4高熵合金中fcc结构的纳米孪晶组织的形成。     

GRAIN REFINEMENT INDUCED BY REMELTING IN UNDERCOOLED Fe-30at.%Co ALLOYS

1.IntroductionSolidificationofundercooledmeltscanproducetherefinedmicrostructuresincludingdendritesandequiaxedgrainsthatareexpectedtoresultintheimprovementofmechanicalproperties.Itisgenerallybelievedthatthegrainrefinementoccurswhentheunderco0l-ingislargerthanthecriticalunderc0olinginsomealloys.Severalmechanismshavebeensuggestedtoaccountf0rtherefinement.Walkerdemonstratedthattheoccurrenceofgrainrefinementinundercooledmeltsisduet0thepressurepulsewhichhasbeende-tectedbytheemissi0nofasound.avel1].…     

Understanding Solid-Solid (fcc→ω+bcc) Transition at Atomic Scale

An atomic transition model of a face-centered cubic (fcc) crystal to a primitive hexagonal ω and body-centered cubic (bcc) structures has been crystallographically built. The fcc structure can transform into the ω structure through a local shuffling or displacement of atoms about 0.4014 Å in iron for a _{fcc iron} = 3.59 Å. The bcc structure can form either after the ω formation or concurrently by the similar mechanism, or the ω structure can be treated as an intermediate stage during the transition of fcc → bcc. Such a transition (fcc → ω + bcc transition) can be confirmed by Widmanstätten pattern formed in an iron meteorite, pearlitic structure and martensite composed of bcc-ferrite and ultra-fine ω particles in iron-carbon steels. The present fcc-bcc orientation relationship matches with Pitsch’s one.     

INFLUENCE OF PHASE COMPOSITION ON PITTING CORROSION RESISTANCE OF SPUTTERED COATING OF 1Cr18Ni9Ti STAINLESS STEEL

A series of single bcc,bcc plus fcc duplex and single fcc microcrystalline coatings of1Cr18Ni9Ti stainless steel were prepared by using sputtering technique.The resistanceagainst pitting corrosion was studied by measurements of pitting corrosion potentials andelectrochemical noise during initiation of corrosion pits.The results show that the sputteredcoatings with single bcc phase or single fcc structure are more resistant to pitting corrosionthan those with bcc plus fcc duplex phase structure.     

连续升温、降温过程中纯Fe的微观结构分析

通过分子动力学模拟,采用较先进的键型指数法HA及原子团类型指数法CTIM-2,对Fe连续升温、降温过程中微观结构进行模拟研究.结果表明:连续升温过程,Fe的微观结构变化是bcc→fcc\hcp→bcc→液体；连续降温过程,Fe的微观结构变化是液体→fcc\hcp.Fe凝固结束没有形成大量的高温bcc晶体,原因是在高温液态中bcc结构原子稳定性较差,fcc和hcp结构原子更易稳定存在.此外,温度变化速率过快,可诱导晶体生长过程中发生层错,促使Fe在升温、降温过程出现fcc和hcp晶体的交替分层分布,这与fcc和hcp晶体的原子能量相近、晶体的致密度相同、原子空间堆垛方式局部相同有关.