Preparation of Fe-based monodisperse spherical particles with fully glassy phase

In this study, we prepared monodisperse spherical particles of a desired diameter using [(Fe_0.5Co_0.5)_0.75B_0.2Si_0.05]₉₆Nb₄ alloy; the particles were prepared by using an atomization process developed by us. The particles have perfect sphericity and narrow size distribution along with a homogeneous composition. The phase transitions of particles from the fully glassy phase to the crystalline phase via mixed phase structures occurred as the particle diameter was increased; the particles produced in the fully glassy phase in an argon atmosphere had a diameter of less than 300 μm. This allowed the estimation of the intrinsic critical cooling rate for the particles with a fully glassy phase, R_c:R_c varied in the range of 700-900 K/s and depended only on the initial temperature of the alloy melt.     

Defect structures in ZrCo2 Laves phase

Point defect structures in the C15 ZrCo₂ alloys were studied by bulk density and X-ray lattice parameter measurements. It was found that, for the ZrCo₂ alloys quenched from 1000°C, the lattice parameter increases linearly as the Zr content increases up to 33.3 at.% Zr. The lattice parameter of the Laves phase remains constant for the alloys with Zr content higher than 33.3 at.%, indicating that the solubility range of Zr in ZrCo₂ on the Zr-rich side is essentially zero. The constitutional defects were found to be of the anti-site type. Thermal vacancies exhibiting a maximum at the stoichiometric composition were observed in the ZrCo₂ Laves phase alloys after quenching from 1250 and 1000°C, with higher thermal vacancies obtained from 1250°C. The defect structures in the ZrCo₂ phase may be correlated to the relative magnitude of formation enthalpies for anti-site and quadruple defects in this compound. Thermal vacancy concentration at a level of 1% in ZrCo₂ does not affect fracture toughness at room temperature.     

Changes in the grain and fine structures of palladium as a result of hydrogen phase naklep

Changes in the grain and fine structures of palladium that occur after the occurrence of reverse β → α hydride phase transformation in the metal are studied. It is shown that hydrogen treatment does not change the microstructure of palladium but strongly affects its fine structure. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 3, pp. 49–54, March, 2007.     

立方相对超细晶梯度硬质合金微观组织的影响

以超细WC粉末为原料,采用低压预烧结和梯度烧结两步法制备了超细晶梯度硬质合金。通过添加不同的立方相,研究了立方相对超细晶梯度硬质合金组织和性能的影响。结果表明,仅添加Ti(C,N)可以形成较厚的梯度层,但梯度烧结后WC晶粒尺寸有较大的增长。(W,Ti)C和(Nb,Ta)C的加入不利于较厚梯度层的形成,但在梯度烧结过程中可以抑制WC晶粒的生长。添加(Ti,W)C的合金在梯度烧结后出现了少量尺寸大于1 μm的WC晶粒,(Ta,Nb)C的加入可以很好的抑制合金中芯环结构立方相的形成。     

Combustion synthesis and characterization of highly crystalline single phase nickel ferrite nanoparticles

A combustion route of synthesizing highly crystalline single phase nickel ferrite (NiFe₂O₄) spinel nanoparticles using various amounts of dl-alanine as fuel has been reported in this paper. The role of the amount of fuel is found to be significant in the size control and phase purity of nano crystalline samples. The structural, thermal, morphological and magnetic studies have been carried out. XRD patterns reveal the formation of highly crystalline nano NiFe₂O₄ with high degree of phase purity when fuel concentration is maintained at 1 M and 2 M. FTIR spectra also prove the formation of pure nano NiFe₂O₄. The temperature and fuel effects are found to have strong influence on size, structural, and magnetic properties of materials. The magnetic measurements show that the nano NiFe₂O₄ samples exhibit soft ferromagnetism with the highest saturation magnetization Ms at room temperature as 42.53 emu/g.     

Mechanical properties of a FeCuSiB alloy with amorphous and/or crystalline structures

Fe_76.5Cu₁Si_13.5B₉ alloy rods with a diameter of 3 mm were fabricated using the copper mold suction casting method. Structural characterization revealed that different parts of the rods have different microstructures that comprise a complete amorphous structure, an amorphous-crystalline composite structure and a complete crystalline structure. Compression and nanoindentation testing showed that the hardness, strength and elastic modulus of the alloy increase with the crystalline component. High crack propagation rate and narrow shear bands contribute to the local melting and softening for the complete amorphous structure although it exhibits the lowest calculated value of the static elastic energy density.     

Dual phase metallic glassy composites with large-size and ultra-high strength fabricated by spark plasma sintering

Two-phase bulk metallic glasses (BMGs) have attracted increasing interest since phase separation might produce metallic glasses with new physical and mechanical properties. In this study, we fabricated the dual phase glassy BMG composites by a spark plasma sintering process using a mixed powder of the gas-atomized Ni-based and Fe-based metallic glassy alloy powders. The thermal stability, microstructure, mechanical and magnetic properties of the obtained dual-phase glassy composites were investigated. The dual-phase glassy composites exhibited ultra-high strength and good soft magnetic properties which satisfy large-size requirements.     

Preparation and crystalline phase of a TiO2 porous film by anodic oxidation

Anatase titanium dioxide is an active photocatalyst, but it is difficult to immobilize on the substrate. A crystalline TiO2 porous film was prepared directly on the surface of pure titanium by anodic oxidation in this work. Constant voltage and constant current anodic oxidation were adopted with sulphuric acid used as the electrolyte, pure titanium as the anode and copper as the cathode. The morphology and structure of the porous film on the substrate were analyzed with the aid of Field Emission Scanning Electron Microscopy （FESEM） and X-ray Diffraction （XRD）. The effects of the parameters of anodic oxidation （such as voltage, the concentration of sulphuric acid, anodization time and current density） on the aperture and the crystalline phase of the TiO2 porous film were systematically investigated. The results indicate that the increase of current density facilitates the augment of the aperture and the generation of anatase and mille. In addition, the forming mechanism of anatase and mille TiO2 porous films was discussed.     

Surface modelling on heavy atom crystalline compounds: HfO2 and UO2 fluorite structures

The study of the bulk and surface properties of cubic (fluorite structure) HfO₂ and UO₂ was performed using the hybrid Hartree–Fock density functional theory linear combination of atomic orbitals simulations via the CRYSTAL06 computer code. The Stuttgart small-core pseudopotentials and corresponding basis sets were used for the core–valence interactions. The influence of relativistic effects on the structure and properties of the systems was studied. It was found that surface properties of Mott–Hubbard dielectric UO₂ differ from those found for other metal oxides with the closed-shell configuration of d-electrons.     

Comparative analyses of Nd (4f) energy level structures in various crystalline hosts

We have performed an in-depth analysis of the energy-level structures in seven Nd³⁺ (4f³) crystal systems: [Nd(H₂O)₉]·3CF₃SO₃, Nd³⁺: Cs₂NaGdCl₈, four Nd³⁺-doped garnets (Nd³⁺: A₃B₅O₁₂), and Nd³⁺: CsCdBr₃. A model Hamiltonian employing 20 free-ion operators and the appropriate one-electron crystal-field interaction operators (plus selected two-particle correlation crystal-field (CFF) operators) was diagonalized within the full 364 SLJM, basis of the f³ electronic configuration. Ample spectroscopic experimental data allowed us to use least-squares fitting routines to produce a crystal-field energy-level structure for Nd³⁺ in each host. Particular attention is given in this report to some differences in the values of the free-ion parameters among the seven hosts and to the strong effects of three CCF operators on crystal-field level ordering in specific multiplets. The effects of CCF operators (originally proposed by Judd and later studies by Reid) are shown to be a small perturbation on the standard one-particle (B_q^k) formalism.     

Length and angle measurements using regular crystalline lattice as reference

In this article, we report on the length and angle measurement methods using a regular crystalline lattice as the reference and a scanning tunneling microscope (STM) as a detector. (1) The feasibility of a comparative length measurement in the range of >5 μm using a regular crystalline lattice as the reference scale and a dual tunneling unit–STM (DTU–STM) as a detector is discussed. In order to reduce the thermal deformation effect, the DTU–STM was made with ultra-low thermal expansion material and a temperature control cell was used. A 5-μm-long atomic image of a highly oriented pyrolytic graphite (HOPG) crystal along the fast scanning axis was obtained using the DTU–STM in the temperature control cell. (2) An unit-angle measurement with nanoradian resolution by referring atomic structure (=crystalline axes) on crystalline surface is proposed. Design and a operation method of a unit-angle measuring machine using the HOPG crystalline surface and the STM is discussed.     

X-ray diffraction phase analysis of crystalline copper corrosion products after treatment in different chloride solutions

The corrosion products Cu₂(OH)₃Cl, Cu₂O, and CuCl₂ were identified on the surface of copper plates after their four days treating in three different sodium chloride, sodium/magnesium, and sodium/calcium chloride solutions using X-ray diffraction powder analysis. However, the quantitative proportions of individual corrosion products differ and depend on the type of chloride solution used. Treating of copper plates only in the sodium chloride solution produced the mixture of corrosion products where Cu₂O is prevailing over the Cu₂(OH)₃Cl and CuCl₂ was not identified. The sample developed after treating of the cooper surface in the sodium/magnesium chloride solution contains Cu₂(OH)₃Cl and CuCl₂ prevailing over the Cu₂O, while the sample developed after treatment of copper in sodium/calcium chloride solution contains Cu₂(OH)₃Cl prevailing over CuCl₂ and Cu₂O was not identified.     

X-Ray and neutron diffraction studies of atomic scale structures of crystalline and amorphous TbFe2Dx

Both X-ray and neutron diffraction techniques were employed in order to elucidate short-range structures of crystalline (c-)TbFe₂D_3.8 and amorphous (a-)TbFe₂D_x (x=3.0, 2.0) prepared by deuterium absorption of the C15 Laves phase compound TbFe₂. Interatomic distances and coordination numbers were derived from the radial distribution functions, RDF(r)s. The RDF(r)s observed by X-ray diffraction indicated that c-TbFe₂D_3.8 adopts a rhombohedral structure, but there is a little difference in the arrangement of metal atoms between the original C15 Laves phase c-TbFe₂ and the rhombohedral c-TbFe₂D_3.8. In contrast, our results indicated that there is a large difference in the arrangement of metal atoms between c-TbFe₂ and a-TbFe₂D_x (x=3.0, 2.0) and there are clusters of Fe and Tb atoms in a-TbFe₂D_x (x=3.0, 2.0). RDF(r)s observed by the neutron diffraction indicated that the D atoms occupy tetrahedral sites consisting of 2Tb+2Fe in c-TbFe₂D_3.8, while they occupy sites consisting of 4Tb, 3Tb+1Fe and 2Tb+2Fe in a-TbFe₂D_x (x=3.0, 2.0).     

Deformation characteristics and dislocation structures in single phase gamma titanium aluminides

The yield stress curves of gamma Ti–Al alloys exhibit three characteristic regimes: normal behavior below RT; anomalous hardening above RT up to 1073 K; and softening above 1073 K. Furthermore, the CRSS curves of single crystal Ti–56Al show orientation-dependent deformation in addition to the temperature dependence. The orientation dependent deformation of the CRSS under single slip of ordinary dislocations at high temperatures was found to be associated with cross-slip in {110) planes. The activation energy of the cross-slip was found to be 0.45 eV. Similar temperature and orientation dependence of the CRSS in single slip of <101] superdislocations occurs by two different processes, each of which at the different temperature range. The one occurring at the low temperature range is associated with {111} cross-slip while the other at the high temperature range is identifiable with (010) cross-slip. In the temperature-change experiments of yield stress, the ordinary slip showed thermal irreversibility while <101] superdislocations exhibited partial reversibility. Such irreversibility appears to be associated with the temperature dependence of cross-slip mode.     

Specific volume and elastic properties of glassy,icosahedral quasicrystalline and crystalline phases in Zr–Ni–Cu–Al–Pd alloy

Elastic properties, phase composition, microstructure and specific volume changes in the Zr₆₅Ni₁₀Cu₅Al_7.5 Pd_12.5 glassy alloy during progressive devitrification have been studied by ultrasonic pulse, X-ray diffractometry, transmission electron microscopy and Archimedean methods, respectively, in terms of structure and properties change. On heating the glassy alloy initially forms an icosahedral phase and then a mixture of tI12 Zr₂Ni^ss and β-Zr^ss crystalline phases after annealing at 993 K for 300 s, and lastly tI12 Zr₂Ni^ss, tI6 Zr₂Pd and hP9 Zr₆Al₂Ni crystalline phases after prolonged annealing at 993 K for 7.2 ks. In an as-solidified state the alloy shows high Poisson’s and K/G ratios of 0.42 and 7, respectively. These parameters are responsible for its good ductility. The structural changes are accompanied by decreases in specific volume, bulk modulus, Lamé parameter and Poisson’s ratio. Small specific volume changes upon primary devitrification suggest a close relation between the glassy and the icosahedral structures. The existence of the icosahedral local order, which exhibits rigidity for three-dimensional shear deformation with mixed mode II mode III, may be responsible for good elasticity of the glassy alloy.     

Programmed strengthening of crystalline materials using copper and aluminum as an example

Fundamental propositions of the well-known method of programmed strengthening of crystalline solids are described. It is shown that when mechanical (deformation) and thermal (tempering, annealing, and aging) actions are combined, the loading rate is determined by the rate of diffusion and microshear processes of relaxation of internal stresses in regions of defect accumulation and by the formation of stable complexes as a result of directional diffusion of point defects.     

Phase formation and structures of quasicrystals and approximants in the Zn–Mg–(Ti, Zr, Hf) system

The compositional regions for primitive (P) and face-centered (F) icosahedral quasicrystals (iQc) have been determined to be around Zn₈₄Mg₉Zr₇ and Zn₇₅Mg₁₈Zr₆, respectively. A 1/1 approximant of the F-type iQc was found to have a composition around Zn₇₇Mg₁₈Zr₅. A similar tendency has been verified for the Zn–Mg–Hf system. No stable iQc was observed in the Zn–Mg–Ti system. High-resolution X-ray measurements performed with synchrotron radiation showed that the stable iQcs are highly ordered and contain less phason disorder. High-angle annular dark field (HAADF) scanning transmission electron microscopy observation of the 1/1 Zn–Mg–Hf approximant effectively revealed the Hf positions in the structure, whose local contrasts can be reasonably interpreted by a structural model where icosahedral and dodecahedral Hf clusters are mutually interpenetrated. Similar appearances of local contrasts were frequently observed in HAADF images of the F-type iQc, indicating that the iQc structure is also build up of icosahedral clusters that are almost identical to those in the 1/1 approximant.