On the mechanism of nucleation of copper precipitates upon aging of Fe-Cu alloys

Structure of the Fe-5.5% Cu alloy has been studied after aging at 500°C to show that the lattice of copper precipitates changes with increasing time of holding at a temperature from bcc to 9R to fcc. The free energy of the solid solutions and the phase-separation diagrams of the bcc and fcc phases of copper have been calculated. Barriers for the nucleation of copper particles with the bcc and fcc lattices have been evaluated. Factors that favor the appearance of intermediate structural forms of copper, which precede the formation of the stable fcc phase, are discussed.     

Electrocatalysis under Conditions of Ion Co-discharge with the Formation of an Alloy

The distribution of elements in Ni–Cr alloy deposits is studied with the use of x-ray photoelectron spectroscopy and electron Auger spectroscopy. Nickel is shown to catalyze the deposition of chromium, while chromium catalyzes the reduction of oxalates to carbon. The alloys have nanocrystal fcc structures based on nickel lattice. At a high chromium content (88 at. %), a phase with hexagonal lattice forms.     

The effect of melt-spinning processing parameters on crystal structure and magnetic properties in Fe–Mn–Ga alloys

We have succeeded to fabricate body-centered cubic (bcc) single phase of Fe–Mn–Ga alloys using melt-spinning technique. Heusler type L2₁ structure of Fe₂MnGa alloy are predicted to have half-metallic properties, however bulk Fe₂MnGa alloys crystallize into face-centered cubic (fcc) lattice with small admixture of bcc phase. By changing either ejection temperature or rotation speed of melt-spinning processing parameters, fcc or bcc lattice can be obtained from same precursor ingot. For stoichiometric Fe₂MnGa as-spun alloy, super-lattice diffraction peaks indicative of L2₁ structure are observed from XRD measurements. The as-spun bcc alloys transform into ferromagnetic hexagonal lattice by thermal annealing.     

First-principles investigation of the Cu–Ni,Cu–Pd,and Ni–Pd binary alloy systems

Phase diagrams of copper–nickel–palladium binary alloys were determined by density functional theory cluster expansion method. The system has both magnetic and non-magnetic binaries and subtle phase coexistence areas between similar and different kind of lattice types. Furthermore, the CuPd binary has several ordered structures. Cluster expansion models were constructed by heuristic cluster selection for all of the fcc structures and for the CuPd_bcc structure. Both configurational and magnetic phase diagrams were determined. Small amount of nickel magnetize fcc palladium to 0.26 μ_B from which the magnetic moment rises almost linearly to that of pure Ni. In CuNi, 0.46 x-Ni is needed for the magnetic transition. In CuPd alloy in 0 K, configurational free energy difference between bcc and fcc lattice resulting to phase separation is only about 1.1 kJ/mol-atoms. Low temperature energetics and magnetic phase diagrams have good quantitative agreement with available experimental and theoretical results. Finite temperature properties of the alloys are in good qualitative agreement with experimental results.     

退火对Ni-W合金药型罩组织与性能的影响

用电沉积方法制备了含钨1.76%(质量分数)的Ni-W合金药型罩。通过拉伸试验对原始电铸态和热处理后样品的力学性能进行了评价,并利用X射线衍射、透射电子显微镜、俄歇电子能谱等技术对原始电铸态和热处理后样品的微观结构进行了分析。结果表明,通过电铸技术制备的Ni-W合金药型罩材料强度较高,晶粒细小并具有(111)织构。制备的Ni-W合金仍具有面心立方结构,W固溶在Ni的晶格中。Ni-W合金药型罩材料经300℃退火后,晶粒发生异常长大,(111)织构转变为(220)织构。经500℃退火后,由于硫在晶界的偏析,发生沿晶断裂,严重影响了材料的力学性能。     

Nanoindentation study on the creep characteristics of high-entropy alloy films: fcc versus bcc structures

Using the magnetron sputtering technique, two typical high-entropy alloy (HEA) films namely CoCrFeNiCu (Al-0) with a face-centered cubic (fcc) structure and CoCrFeNiCuAl_2.5 (Al-2.5) with a body-centered cubic (bcc) structure were prepared by alloy targets. The as-deposited HEA films have a columnar-growth mode and nanocrystalline grains. The creep behaviors of both HEA films were systematically investigated by nanoindentation with a Berkovich indenter. The bcc Al-2.5 exhibited a stronger creep resistance than the fcc Al-0. In addition, with the increase of holding load and/or loading rate, the creep deformation was significantly enhanced in the fcc Al-0. Interestingly, it was almost history-independent in the bcc Al-2.5. The creep characteristics of HEA films could be related to the distinct lattice structures, which apparently affect the kinetics of plastic deformation. The strain rate sensitivity (SRS) and activation volume of the dislocation nucleation were carefully estimated for both HEA films. In view of the large differences of activation volumes between Al-0 and Al-2.5, we present discussions to explain the observed creep characteristics in HEA films.     

AgCuZnNi合金铸态组织及凝固路径分析

采用扫描电子显微镜、能谱仪以及X射线衍射等技术,对Ag-18Cu-30Zn-2Ni合金的铸态组织、相组成及结构进行了分析。结果表明,合金主要由白色基体、细小片层状共晶胞及直径为2~6μm的黑色颗粒相组成;铸态合金的物相组成为面心立方(fcc)晶格结构的Ag基固溶体相、灰色层状共晶相(Ag+Cu64Zn36)及简单立方(sc)晶格结构的近球形黑色颗粒Cu2Ni Zn相;Ag Cu Zn Ni合金的平衡凝固路径为:L→L+γ→(L+α1)+γ→((α2+β)+α1)+γ。     

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。     

Study of δ-hydrides in Ti-2Al-2.5Zr and Ti-4Al-2V alloys

The α alloy Ti-2Al-2.5Zr and near α alloy Ti-4Al-2V were hydrogenated to various levels. The morphology,orientation relation (OR), and habit plane of the hydrides were studied by means of transmission electron microscopy (TEM). It was found that in the two alloys most of the precipitates are δ-hydrides which have fcc structure with the lattice parameter a = 0.44 nm. Two basic orientation relationships and habit planes of the precipitates are determined. Twin structure was observed in both alloys.     

Design of new face-centered cubic high entropy alloys by thermodynamic calculation

A new face-centered cubic (fcc) high entropy alloy system with non-equiatomic compositions has been designed by utilizing a CALculation of PHAse Diagram (CALPHAD) - type thermodynamic calculation technique. The new alloy system is based on the representative fcc high entropy alloy, the Cantor alloy which is an equiatomic Co- Cr-Fe-Mn-Ni five-component alloy, but fully or partly replace the cobalt by vanadium and is of non-equiatomic compositions. Alloy compositions expected to have an fcc single-phase structure between 700 °C and melting temperatures are proposed. All the proposed alloys are experimentally confirmed to have the fcc single-phase during materials processes (> 800 °C), through an X-ray diffraction analysis. It is shown that there are more chances to find fcc single-phase high entropy alloys if paying attention to non-equiatomic composition regions and that the CALPHAD thermodynamic calculation can be an efficient tool for it. An alloy design technique based on thermodynamic calculation is demonstrated and the applicability and limitation of the approach as a design tool for high entropy alloys is discussed.     

Structure and phase formation in Cu–Mn alloy thin films deposited at room temperature

Transmission electron microscopy characterization of Cu–Mn alloy thin films deposited by DC magnetron sputtering is applied to reveal the formation of phases throughout the composition range. Pure Cu and Mn films exhibit face-centred cubic (fcc) Cu and α-Mn phases, respectively. At room temperature the low Mn content films have fcc structure (γ-phase). Mn can substitute Cu in the fcc Cu lattice up to ～35 at.% Mn. The lattice parameter of fcc Cu–Mn alloy films follows a linear relationship of a₀ = a_Cu + 0.322c (in Å), where a_Cu = 3.615 Å is the lattice parameter of Cu and c is the Mn atomic concentration. At high Mn content, above 50 at.% Mn, a homogeneous one-phase structure is observed, possessing the short-range order of α-Mn. The incorporation of Cu into Mn suggests that this structure changes from crystalline α-Mn to disordered structure as the Cu content increases. A narrow two-phase region exists between 35 and 45 at.% Mn. A grain size minimum of 2–3 nm was observed in the 35–65 at.% Mn region.     

A new theoretical approach to the thermodynamic calculation of high-temperature oxidation of Ni-Cr alloys

In calculations, not only the Gibbs formation energy of nickel and chromium oxides and thermodynamic activities of the alloy components, but also the Gibbs surface energy of a Ni-Cr alloy is taken into account. The method is based on the adsorption model of the alloy oxidation, according to which the adsorption of an alloy component with the smaller surface energy, namely, nickel, at the alloy-oxide film interface boundary shifts the dynamic equilibrium between the alloy and oxide-film components toward the formation of NiO. For the oxidation of Ni-Cr alloys, which are solid solutions with an fcc lattice, at 1123 to 1473 K, concentration boundaries of the chromium content in the alloy are calculated for the case of the prevailing formation of Cr₂O₃ oxide, which determines the high heat resistance of Ni-Cr alloys. Original Russian Text ? Yu.Ya. Andreev, A.A. Shumkin, 2006, published in Zashchita Metallov, 2006, Vol. 42, No. 3, pp. 239–244.     

退火对AlCoCrFeMnTi高熵合金相组成与显微形貌的影响

为了研究退火温度对AlCoCrFeMnTi高熵合金的物相结构、显微组织及硬度的影响,分别采用X射线衍射仪、光学显微镜、扫描电镜和显微硬度计对不同退火温度下AlCoCrFeMnTi合金进行了测试。结果表明:铸态AlCoCrFeMnTi高熵合金物相结构是由bcc主相和fcc相双相组成,且其各相衍射峰普遍较宽,这是由于原子半径差较大和冷却速度快引起的晶格畸变所致。600 ℃退火后,合金中形成了新的hcp相,当退火温度为800 ℃和1000 ℃时,合金衍射峰的峰形并未再发生显著变化。铸态和退火后的AlCoCrFeMnTi合金均为典型的树枝晶结构,1000 ℃退火后的扫描电镜照片中发现了典型的调幅分解组织。合金硬度值在铸态最大,达到了750 HV0.5,随着退火温度升高硬度逐步降低。在经过1000 ℃退火后,一方面由于合金中出现调幅分解组织,使得过饱和的原子大量析出,降低了晶格畸变程度,导致硬度下降;另一方面,由于退火温度的升高,加速了原子的扩散能力,降低了合金内部的内应力,此时合金硬度下降到604.9 HV0.5。     

HRTEM studies of cobalt-filled carbon nanotubes

Cobalt-filled carbon nanotubes were synthesized at high temperature and high gas pressure. A high-resolution transmission electron microscopy study demonstrates that the product of the synthesis contains cylindrical carbon nanotubes whose cores are filled with cobalt nanoparticles or nanorods. It is shown that cobalt appears inside the nanotubes in three basic modifications: face-centered cubic (fcc) lattice, hexagonal close-packed (hcp) lattice and disordered polytypic structure. The fcc lattice is often twinned, with two or more non-parallel twinning planes being observed. The orientations of the fcc and hcp cobalt particles with respect to the nanotubes were investigated. The authors believe that the variety of cobalt modifications inside the nanotubes is due to the process of segregation of the closely packed structures from the melt.     

基于SLM成形的TC4钛合金点阵结构设计及压缩行为研究

采用选区激光熔化(SLM)技术成形TC4钛合金均匀与梯度点阵结构,研究了不同杆径(0.8~1.2mm)、单胞类型(bcc、fcc、fbcc)、添加竖向支杆(bccz、fccz、fbccz)对均匀与梯度形式点阵结构压缩性能及能量吸收的影响规律。结果表明：1.2mm杆径点阵结构性能最优;fccz与fbccz点阵结构分别在同质量与同体积下具有最佳的性能;竖向支杆的存在能够大幅的增强点阵结构在特定加载条件下的性能;均匀点阵结构在失效前的压缩性能与能量吸收优于相同相对密度及应变的梯度点阵结构,由于梯度点阵结构逐层断裂的特性,在50%及更大应变的状态下具有更优的性能,更适于应用在吸能装置。     

氢处理对TC21合金显微组织的影响

利用XRD、OM和TEM研究两相钛合金TC21置氢前后以及除氢后的显微组织变化.研究发现:随着氢含量的增加,TC21合金中的β相逐渐增加,当氢含量达到0.319%(质量分数,下同)以上时,试样中出现面心立方的氢化物δ.氢化物主要是在高温置氢后冷却过程中通过扩散方式发生共析反应形成的.由于共析反应所造成的晶格畸变,除氢后发生了再结晶,晶粒组织更加细化.     

NiAl表面能的分子动力学计算

利用嵌入原子类型的势函数，通过分子动力学方法计算了Ｂ２结构标准化计量比ＮｉＡｌ合金的四个低指数晶面在６种温度时的表面能。计算结果表明，表面能随温度的升高呈增加趋势；最密排面的表面能最低；一些表面在高温下发生了重构或成分偏析等表面反应，用类似方法计算了ｆｃｃ结构Ｎｉ的表面能，计算结果与已知实验研究基本一致。     

Metallography of a melt-quenched aluminum-cobalt alloy

Rapid quenching from the melt of an Al-5 wt.% Co alloy has resulted in the formation of a supersaturated solid solution at very high cooling rates as obtained in the gun technique. With decreasing cooling rate (and increasing thickness of the specimen), e.g., in melt-spun condition, a variety of microstructures has been produced consisting of fine dendritic patterns, cellular-dendritic structures, and precipitation of coarse intermetallic particles. Two metastable phases have also been detected—one with a bcc structure and a = 0.286 nm corresponding to β-AlCo, and the other having an fcc structure with a lattice parameter a = 0.52 nm. Electron microscopy, electron diffraction, and x-ray microanalysis have been extensively employed to fully characterize the phases present in the melt-quenched alloy.     

Noncollinear magnetism of Fe-rich Fe-Ni alloys

The magnetic structure of Fe-rich FeNi alloys has long been a subject of great scientific interest and controversy. In this study, the authors attempt to understand an interesting phenomenon that the average magnetic moment of the alloys in the γ-phase (fcc) decreases dramatically in the composition range near 70% Fe. Although the observation was made more than 30 years ago, the nature of the mechanism for this moment collapse is still controversial. In this approach, the noncollinear locally self-consistent multiple-scattering (LSMS) method is applied to the magnetic structure calculation of large unit cell samples consisting of Fe and Ni atoms. The Fe and Ni atoms are randomly distributed on a fcc lattice. The moment directions are initialized to be randomly oriented and then, as the self-consistent iterations proceed, are allowed to rotate to minimize the total energy. Astable magnetic structure of the alloy is determined by the final moment configuration. Results are compared with experiments and the possible existence of noncollinear magnetic structures are discussed.