Phase Stability and Transformations in the Zr<Subscript>2</Subscript>Ni<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Cu<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> Amorphous System

Since Ni and Cu differ by only one valence electron, yet have nearly identical atomic sizes (1.27 vs 1.28 Å for Cu and Ni, respectively), the amorphous Zr₂Ni _x Cu_1?x system is ideal for isolating the effects of electronic structure on short- and medium-range order and the concomitant influence of both the structure and order on devitrification pathways. Thermal analysis, time-resolved high-energy X-ray diffraction (HEXRD), and transmission electron microscopy (TEM) were used to follow metastable and stable crystalline phase formation during devitrification. Using HEXRD, we observed that the first devitrification product in the Zr₂Ni system is the C16 structure, if oxygen is kept sufficiently low, while the Zr₂Cu system forms the C11b structure. For x = 0.25, the initial devitrification involves forming coexisting C11b and C16 phases. When Ni is increased to x ≥ 0.50, the initial devitrification only involves the C16 structure. These results are in complete accord with electronic structure calculations showing that the enthalpy of formation for the C11b phase is favored for x = 0, while enthalpies for C11b and C16 are nearly identical for x = 0.25; the C16 phase has the most negative enthalpy for all compositions in which x > 0.25.     

Elasticity of Ni<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>W<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> (<Emphasis Type="Italic">x</Emphasis> ≤ 0.1875) Alloys from First Principles Calculations

The elastic properties of Ni _x W_1?x alloys up to x = 0.1875 have been determined from first principles calculations. We have used stress–strain relationships to calculate the C _ij elastic coefficients and the Voigt–Reuss–Hill approximations to determine the bulk and shear moduli of polycrystals. The W alloying increases the compression modulus while the shear modulus remains almost constant. Furthermore, the W alloying has a minor effect on the elastic anisotropy and, therefore, on its contribution to the indentation modulus.     

Synthesis and structural characterization of nanocrystalline Ni<Subscript>50</Subscript>Al<Subscript>50 − <Emphasis Type="Italic">x</Emphasis></Subscript>Mo<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> intermetallic compound prepared by mechanical alloying

Nanocrystalline Ni₅₀Al_{50 ? x} Mo _x (x = 0, 0.5, 1, 2.5, and 5) intermetallic powders were synthesized by mechanical alloying (MA). Microstructural characterization and structural changes of powder particles during mechanical alloying were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results confirmed that the synthesis behavior of NiAl intermetallic depends on the Mo content and milling time. The SEM micrograph outcomes confirmed the specimen with longer milling time includes finer and more homogenous particles with attention to the ones with lesser milling time. Mo enhance has a considerable effect on the lowering of crystallite size. The TEM image showed that the Ni₅₀Al₄₅Mo₅ nano-particles were less than 10 nm.     

<Emphasis Type=Italic>In-Situ</Emphasis> Scanning Electron Microscopy/Electron Backscattered Diffraction Observation of Microstructural Evolution during <Emphasis Type=Italic>α</Emphasis> → <Emphasis Type=Italic>γ</Emphasis> Phase Transformation in Deformed Fe-Ni Alloy

This article presents in-situ observation of ferrite (α)/austenite (γ) phase transformation in an Fe-8.5 at. pct Ni alloy deformed by rolling using an automated scanning electron microscopy/energy backscattered diffraction (SEM/EBSD) system. During heating, recrystallization in α phase and α → γ phase transformation independently occurred. The γ grains nucleated in unrecrystallized α grains were most probably incorporated into the grain interior of recrystallized α grains. They did not have any specific orientation relation (OR) with recrystallized α grains and grew in an isotropic manner. On the other hand, the intragranular γ grains nucleated in recrystallized α grains had a Kurdjumov–Sachs (K-S) OR with the α grains and grew in a considerably anisotropic manner. They preferentially grew along the common direction of surface traces of {110} _α /{111} _γ . Approximately half of grain boundary (GB) allotriomorphs had either the K-S OR or the Nishiyama–Wasserman (N-W) OR with the parent α grains. The γ allotriomorphs predominantly grew into the α grain having the special OR with themselves. The GB character distribution of γ phase at high temperatures was measured. The fraction of CSL boundaries was as high as 63 pct, particularly that of Σ3 grain boundaries (GBs) was 54 pct.     

Magnetic states in Fe<Subscript>65</Subscript>(Ni<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)<Subscript>35</Subscript> alloys

The ferromagnetic-antiferromagnetic concentration transition in Fe₆₅(Ni_{1 − x} Mn _x )₃₅ alloys is studied by neutron diffraction and small-angle magnetic neutron scattering (SMNS). The Curie and Néel temperatures are measured, and the antiferromagnetic moments and the cross sections of SMNS by magnetic heterogeneities are determined. The parameters of spin density fluctuations in the heterogeneities are obtained. A cluster mechanism of the nucleation of magnetic phases is revealed, and the spin-glass freezing temperatures are estimated. A low-temperature diagram is constructed for the magnetic states of the alloys.     

Synthesis and Electrochemical Properties of Lithium–Vanadium Li<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>V<Subscript>2</Subscript>O<Subscript>5</Subscript> (<Emphasis Type="Italic">x</Emphasis> = 0.1–0.3) Bronzes

Lithium–vanadium Li _x V₂O₅ (x = 0.1–0.3) bronzes are synthesized by solid-phase and soft chemistry methods. Their electrical properties are studied. Cells with an Li _x V₂O₅ cathode and a solid or liquid lithium anode are subjected to electrochemical cycling. The lithium–vanadium bronzes synthesized by the soft chemistry method are shown to have higher electrochemical characteristics.     

Diffusion and Growth of the <Emphasis Type=Italic>μ</Emphasis> Phase (Ni<Subscript>6</Subscript>Nb<Subscript>7</Subscript>) in the Ni-Nb System

Incremental diffusion couple experiments are conducted to determine the average interdiffusion coefficient and the intrinsic diffusion coefficients of the species in the Ni₆Nb₇ (μ phase) in the Ni-Nb system. Further, the tracer diffusion coefficients are calculated from the knowledge of thermodynamic parameters. The diffusion rate of Ni is found to be higher than that of Nb, which indicates higher defect concentration in the Ni sublattice.     

Structure of Zr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Pt<Subscript>100−<Emphasis Type="Italic">x</Emphasis></Subscript> (73 ≤ <Emphasis Type="Italic">x</Emphasis> ≤ 77) Metallic Glasses

The structure of hyper-eutectic Zr _x Pt_100−x (73 ≤ x ≤ 77) metallic glasses produced by melt spinning was examined with high-energy synchrotron X-ray diffraction (HEXRD) and fluctuation electron microscopy. In addition, details of the amorphous structure were studied by combining ab initio molecular dynamics and reverse Monte Carlo simulations. Crystallization pathways in these glasses have been reported to vary dramatically with small changes in compositions; however, in the current study, the structures of the different glasses were also observed to vary with composition, particularly the prepeak in the total structure factor that occurs at a Q value of around 17 nm⁻¹. Results from simulations and fluctuation electron microscopy suggest that the medium-range order of the amorphous structure is characterized by extended groups of Pt-centered clusters that increase in frequency, structural order, or spatial organization at higher Pt contents. These clusters may be related to the Zr₅Pt₃ structure, which contains Pt-centered clusters coordinated by 9Zr and 2Pt atoms. This article is based on a presentation given in the symposium entitled “Bulk Metallic Glasses IV,” which occurred February 25–March 1, 2007 during the TMS Annual Meeting in Orlando, Florida under the auspices of the TMS/ASM Mechanical Behavior of Materials Committee.

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Synthesis of <Emphasis Type=Italic>α</Emphasis>- and <Emphasis Type=Italic>β</Emphasis>-Rhombohedral Boron Powders<Emphasis Type=Italic> via</Emphasis> Gas Phase Thermal Dissociation of Boron Trichloride by Hydrogen

The α-rhombohedral and β-rhombohedral crystal structures of pure elemental boron powders have been synthesized via gas phase thermal dissociation of BCl₃ by H₂ on a quartz substrate. The parameters affecting the crystal structures of the final products and the process efficiency, such as BCl₃/H₂ molar ratio (1/2 and 1/4) and reaction temperature (1173 K to 1373 K [900 °C to 1100 °C]), have been examined. The experimental apparatus of original design has enabled boron powders to be obtained at temperatures lower than those in the literature. The surface/powder separation problem encountered previously with different substrate materials has been avoided. Boron powders have been synthesized with a minimum purity of 99.99 pct after repeated HF leaching. The qualitative analysis of exhaust gases has been conducted using a Fourier transform infrared spectroscope (FTIR). The synthesized powders have been characterized using an X-ray powder diffractometer (XRD) and scanning electron microscope (SEM) techniques. The results of the reactions have been compared with equilibrium predictions performed using the FactSage 6.2 (Center for Research in Computational Thermochemistry, Montreal, Canada) thermochemical software.     

Study of <Emphasis Type=Italic>γ</Emphasis>/<Emphasis Type=Italic>γ</Emphasis>′ Interfaces in Nickel-Based,Single-Crystal Superalloys by Scanning Transmission Electron Microscopy

The interfaces of γ/γ′ in crept Re-bearing, single-crystal, nickel-based superalloys have been studied by scanning transmission electron microscopy. Elements Ni and Ta are congregated at the γ′ side, ahead of the Re enrichment near interfaces, which shows the retarding effect on element diffusion during creep by Re enrichment. A growth step exists at the γ/γ′ interfaces with the apex of kinks congregated with heavy atoms, which may slow down interface displacement during creep.     

A Thermodynamic Model to Estimate the Formation of Complex Nitrides of Al<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Mg<Subscript>(1–<Emphasis Type="Italic">x</Emphasis>)</Subscript>N in Silicon Steel

A complex nitride of Al _x Mg_(1?x)N was observed in silicon steels. A thermodynamic model was developed to predict the ferrite/nitride equilibrium in the Fe-Al-Mg-N alloy system, using published binary solubility products for stoichiometric phases. The model was used to estimate the solubility product of nitride compound, equilibrium ferrite, and nitride compositions, and the amounts of each phase, as a function of steel composition and temperature. In the current model, the molar ratio Al/(Al?+?Mg) in the complex nitride was great due to the low dissolved magnesium in steel. For a steel containing 0.52 wt pct Al_s, 10 ppm T.Mg., and 20 ppm T.N. at 1100 K (827 °C), the complex nitride was expressed by Al_0.99496Mg_0.00504N and the solubility product of this complex nitride was 2.95?×?10^?7. In addition, the solution temperature of the complex nitride increased with increasing the nitrogen and aluminum in steel. The good agreement between the prediction and the detected precipitate compositions validated the current model.     

Grain Boundary Mediated Displacive–Diffusional Formation of <Emphasis Type=Italic>τ</Emphasis>-Phase MnAl

Dynamic in situ heating and postmortem transmission electron microscopy studies, including high-resolution electron microscopy, have been performed for a near equiatomic composition of a Mn-Al-base permanent magnet alloy to investigate the mechanisms of the transformation of hexagonal close-packed ε-phase to a chemically ordered tetragonal τ-phase with a face-centered cubic-related L1₀ structure. Although a “massive” mode dominates the kinetics of this composition invariant transformation, we also observed the genesis of a morphologically plate-like τ-phase by partial dislocation glide, described as Shockley-type partials with respect to the L1₀ structure, and a transformation mode exhibiting displacive characteristics. The sources for the transformation dislocations facilitating the formation of the morphologically plate-like τ-phase were associated with the interfaces between the parent ε- and product τ-phase produced by the “massive” transformation mode. Our experiments revealed diffusional and displacive features of the mechanism accomplishing the formation of τ-MnAl with plate-like morphology. Hence, a hybrid displacive–diffusional mechanism has been identified, and the synergistic role of the nucleation interfaces of the massively transformed τ-phase has been discussed.     

Experimental Characterization and Crystal Plasticity Modeling of Heterogeneous Deformation in Polycrystalline <Emphasis Type=Italic>α</Emphasis>-Ti

Grain-level heterogeneous deformation was studied in a polycrystalline α-Ti specimen deformed by four-point bending. Dislocation slip activity in the microstructure was investigated by surface slip trace analysis. Three-dimensional–X-ray diffraction (3D-XRD) was used to investigate subsurface lattice rotations and to identify geometrically necessary dislocations (GNDs). The slip systems of local GNDs were analyzed by studying the streaking directions of reflections in corresponding Laue patterns. The analysis performed in one grain indicated that the subsurface GNDs were from the same slip system identified using slip trace analysis in backscattered electron images. A crystal plasticity finite element (CPFE) model was used to simulate deformation of the same microstructural region. The predictions of dislocation slip activity match the general aspects of the experimental observations, including the ability to simulate the activation of different slip systems in grains where multiple slip systems were activated. Prediction of local crystal rotations, however, was the least accurate aspect of the CPFE model.     

Analysis of the Fe–Ce–O–C–<Emphasis Type=Italic>M</Emphasis> phase diagrams (<Emphasis Type=Italic>M</Emphasis> = Ca,Mg, Al,Si) by constructing a component-solubility surface

Analysis of the ternary phase diagrams of Ce₂O₃- and CeO₂-containing oxide systems allowed us to find the oxide compounds that form during steel deoxidizing with cerium and with cerium together with aluminum, calcium, magnesium, or silicon. The temperature dependences of the equilibrium constants of formation of Ce₂O₃ oxides and Ce₂O₃ · Al₂O₃, Ce₂O₃ · 11Al₂O₃, Ce₂O₃ · 2SiO₂, 7Ce₂O₃ · 9SiO₂ and Ce₂O₃ · SiO₂ compounds are found. Surfaces for the component solubility in metallic melts Fe–Al–Ce–O–C, Fe- Ca–Ce–O–C, Fe–Mg–Ce–O–C, and Fe–Si–Ce–O–C are constructed. Nonmetallic inclusions that form in the course of experimental melts of St20 steel after its deoxidizing with silicocalcium and rare-earth metal (REM)-containing master alloys in a ladle furnace after degassing are studied. Phase inhomogeneity of the inclusions is found. As a rule, they consist of phases classified into the following three groups: oxide–sulfide, sulfide–oxide, and multiphase oxide–sulfide melt. Calcium aluminates are found to be components of complex sulfide-oxide noncorrosive inclusions.