X-ray spectral investigation of the electronic structure and chemical bonding in ultradispersed powders and the fine-grained materials obtained from them. I. Titanium nitride

The dependence of the electron energy spectrum of ultradispersed TiN powders on particle size was studied by the method of ultrasoft x-ray spectroscopy. A relative narrowing of the x-ray TiL_α and NK_α emission bands (which reflect the energy distribution of valence Np- and Tid-states) depended on the specific surface area of the powders and charge states of the Ti and N atoms. It was shown that narrowing of these bands is due to localization of the Np- and Tid-orbitals of surface atoms as a result of breaking Ti−N bonds. Broadening of the NK_α and TiL_α bands in certain energy ranges was observed after compacting ultradispersed powders. This is a result of Tid and Np orbital splitting caused by the formation of Ti−N bonds between the surface atoms of neighboring particles brought into contact at high pressure and temperature. Institute for Problems of Materials Science, Ukraine National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 7–8(408), pp. 75–85, July–August, 1999.     

Electronic structure and charge state of atoms of cubic and hexagonal tantalum carbides

The electronic structure and charge states of atoms of cubic and hexagonal tantalum carbides have been studied by X-ray photoelectron (XPS) and X-ray absorption (XAS) spectroscopy. The XPS spectra of both valence and core-level electrons as well as the TaL _III XAS spectra of TaC_x have been obtained over the range 0.36≤x≤0.98. In all the tantalum carbides studied charge transfer takes place from Ta to C atoms. The shifts of the Ta 4f core levels and the midpoints of the TaL_III absorption edges indicates that the effective positive charge of the Ta atoms decreases in the row TaC_0.98»TaC_0.36. In that sequence of compounds the main peak of the XPS valence band spectra shifts toward the Fermi level by about 0.85 eV.     

Contribution of electrospark alloying to the oxidation resistance of hard tungsten alloys

The paper examines the contribution of electrospark alloying to the oxidation resistance of hard tungsten alloys. It is established that the oxidation of carbides results from their electronic structure. When WC and hard tungsten alloys are heated to 1000°C, a brittle scale consisting of WO₃ and CoWO₄ rapidly forms. The oxidation resistance reduces as follows: TiC → Co → W → HTA (if TiC is more than 10%) → WC-Co → WC. The oxidation rate of hard tungsten alloys may be a criterion of their serviceability. It is shown that the oxidation resistance of hard tungsten alloys becomes much higher after their electrospark alloying with aluminum, titanium, and chromium and with wear-resistant composite TsLAB-2 ceramics based on the ZrB₂-ZrSi₂-LaB₆ system with Ni-Cr-Al (30 mole%) binder. __________ Translated from Poroshkovaya Metallurgiya, Vol. 47, No. 1–2 (459), pp. 145–150, 2008.     

Features of the fine structure of the X-ray CK α emission bands of multiwalled carbon nanotubes

The electronic structure of multiwalled carbon nanotubes of different diameters fabricated with and without the use of catalysts is investigated by means of ultrasoft x-ray spectroscopy. Nanodimensional narrowing of the CK _α bands of nanotubes with lesser diameter is discovered. A dependence of the electronic structure of multiwalled carbon nanotubes on the type of the catalyst applied is established. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(449), pp. 85–91, May–June, 2006.     

Reactions of niobium and tungsten with phosphorus

X-ray diffraction methods have been applied to the component interaction in the Nb-W-P system in the region of 0–0.67 molar parts of P. An isothermal section of the phase diagram at 1070 K has been constructed. No ternary compounds are formed in the system. The phosphide Nb₃P (structure of Ti₃P type) dissolves tungsten to the limiting composition N_1.8W_1.2P (a = 1.0006(6) nm, c = 0.5073(2) nm). The solubility of tungsten in other niobium phosphides does not exceed 0.05 molar fraction. __________ Translated from Poroshkovaya Metallurgiya, Nos. 7–8(450), pp. 76–80, July–August, 2006.     

Bulk and interface boundary diffusion in group IV hexagonal close-packed metals and alloys

Bulk and grain boundary (GB) self-diffusion and substitutional solute diffusion in group IV hexagonal close-packed (hcp) metals (α-Ti, α-Zr, and α-Hf) are reviewed. The recent results obtained on high-purity materials are shown to approach closely the “intrinsic” diffusion characteristics. The enhancement effect of fast-diffusing impurities (such as Fe, Ni, or Co) is discussed for both self-and substitutional bulk solute diffusion in terms of the interstitial solubility of the impurity atoms. In GB self-diffusion, the impurity effect is found to be less dramatic. The results obtained on high-purity hop materials can be interpreted in terms of intrinsically ‘normal’ vacancy-mediated GB diffusion, with the ratio of GB to volume diffusion activation enthalpies of Q _gb /Q ≈ 0.6. The GB self-diffusion in group IV hcp metals reveals distinct systematics. Bulk self-diffusion and fast interstitial solute diffusion (Fe and Ni) in the hcp phase α ₂-Ti₃Al are reviewed. Interphase boundary diffusion of Ti in the unidirectional lamellar α ₂/γ structure of the two-phase Ti₄₈Al₅₂ alloy is analyzed with respect to the phase boundary structure and GB self-diffusion in α ₂-Ti₃Al. This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee.     

Bulk and interface boundary diffusion in group IV hexagonal close-packed metals and alloys

Bulk and grain boundary (GB) self-diffusion and substitutional solute diffusion in group IV hexagonal close-packed (hcp) metals (α-Ti, α-Zr, and α-Hf) are reviewed. The recent results obtained on high-purity materials are shown to approach closely the “intrinsic” diffusion characteristics. The enhancement effect of fast-diffusing impurities (such as Fe, Ni, or Co) is discussed for both self- and substitutional bulk solute diffusion in terms of the interstitial solubility of the impurity atoms. In GB self-diffusion, the impurity effect is found to be less dramatic. The results obtained on high-purity hcp materials can be interpreted in terms of intrinsically ‘normal’ vacancy-mediated GB diffusion, with the ratio of GB to volume diffusion activation enthalpies of Q _gb /Q ≈ 0.6. The GB self-diffusion in group IV hcp metals reveals distinct systematics. Bulk self-diffusion and fast interstitial solute diffusion (Fe and Ni) in the hcp phase α ₂-Ti₃Al are reviewed. Interphase boundary diffusion of Ti in the unidirectional lamellar α ₂/γ structure of the two-phase Ti₄₈Al₅₂ alloy is analyzed with respect to the phase boundary structure and GB self-diffusion in α ₂-Ti₃Al. This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee.     

Synthesis and characterization of rare earth metal doped tungsten trioxide photocatalyst for degradation of Rhodamine B dye

Nowadays,it is concern for researchers that due to high recombination rate of photogenerated charge carriers in tungsten trioxide(WO₃) nanoparticles,the future applications are limited in the field of photocatalysis.Herein we attempt to synthesize tungsten trioxide nanoparticles with different doping concentrations of lanthanum i.e.2 wt%,4 wt%,6 wt% and 8 wt%.The synthesized samples were characterized by using various characterization techniques:X-ray diffraction(XRD),Raman spectrosco...     

Combustion synthesis of α-Si3N4-(MgO, Y2O3) composites

The possibility of obtaining composite powders of α-Si₃N₄-Y₂O₃ and α-Si₃N₄-MgO by self-propagating high-temperature synthesis (SHS) is studied. It is established that the α → β phase transformation starts at temperatures lower than the melting points of the corresponding eutectics. Metastable composite powders based on α-Si₃N₄ with a high rate of phase transition are obtained. The composite powders (α-Si₃N₄-Y₂O₃, α-Si₃N₄-MgO) are used in hot pressing technology. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 1–2(453), pp. 10–14, 2007.     

Electrochemical synthesis of hard-alloy compositions based on tungsten carbide and an iron triad metal

Single and cyclic voltammetry is used to study the electrode processes that occur during electrochemical synthesis of hard-alloy compositions based on tungsten carbide and an iron triad metal in tungstate and tungstate-carbonate Na₂WO₄-Li₂WO₄-Li₂CO₃ (5.0–22.0 wt %) melts. The conditions of bringing the electroprecipitation potentials of tungsten, carbon, and an iron triad metal into coincidence are determined.     

Structure and stability of a new ternary hexagonal phase in Al<Subscript>3</Subscript> Ti-based Al-Ti-V alloys

A novel hexagonal phase (designated H₍₂₎) has been detected as a major constituent of both Al₆₂Ti₁₀V₂₈ and Al₅₅Ti₁₀V₃₅ alloys, following chill casting and after homogenization at 1523 K. The phase H₂ has an ordered hexagonal crystal structure (space group P6₃/mmc, α=0.558±0.001 and c=0.450±0.001 nm), similar to that of α ₂-Ti₃Al, and an atomic composition of 54±1 Al−11±1 Ti−35±1 V in the chill-cast Al₅₅Ti₁₀V₃₅ alloy. A fine-scale, duplex lamellar structure, developed within the ordered H₂ phase in the solid state, was composed of parallel-sided multivariants of ξ-Ti₅Al₁₁ phase, formed parallel to (0001)_{H 2}. The orientation relationship between constituent phases was of the form

Phase transformation in an Fe-9.0AI-29.5Mn-1.2Si alloy

The microstructure of an (α + γ) duplex Fe-9.0Al-29.5Mn-l.2Si alloy has been investigated by means of transmission electron microscopy. In the as-quenched condition, extremely fine D0₃ particles were formed within the ferrite matrix by a continuous ordering transition during quenching. After being aged at 550 °C, the extremely fine D0₃ particles existing in the as-quenched specimen grew preferentially along (100) directions. With increasing the aging time at 550 °C, a (Si, Mn)-rich phase (designated as “L phase”) began to appear at the regions contiguous to the D0₃ particles. The L phase has never been observed in various Fe-Al-Mn, Fe-Al-Si, Fe-Mn-Si, and Mn-Al-Si alloy systems before. When the as-quenched specimen was aged at temperatures ranging from 550 °C to 950 °C, the phase transformation sequence occurring within the (α + D0₃) region as the aging temperature increases was found to be (α + D0₃ + L phase) → (α + D0₃ + A13 β-Mn)→ (B2 + D0₃ + A13 β-Mn)→ (B2 + A13β-Mn)→ (α + A13 β-Mn)→ (α +γ)→α.     

The effect of additives on the eutectoid transformation of ductile iron

The eutectoid transformation of austenite in cast iron is known to proceed by both the meta-stable γ → α + Fe₃C reaction common in Fe-C alloys of near eutectoid composition, and by the direct γ → α + Graphite reaction, with the graphite phase functioning as a car-bon sink. In addition, the meta-stable cementite constituent of the pearlite can dissolve near the graphite phase (Fe₃C → α + Graphite), producing free ferrite. Isothermal trans-formation studies on a typical ductile iron (nodular cast iron) confirmed that all of these reaction mechanisms are normally operative. The addition of 1.3 pct Mn was found to substantially retard all stages of the transformation by retarding the onset of the eutectoid transformation, decreasing the diffusivity of carbon in ferrite, and stabilizing the cemen-tite. Minor additions of Sb (0.08 pct) or Sn (0.12 pct) were found to inhibit the γ →α + Graphite reaction path, as well as the Fe₃C → α + Graphite dissolution step, but did not significantly affect the meta-stable γ → α + Fe₃C reaction. Scanning Auger microprobe analysis indicated that Sn and Sb adsorb at the nodule/metal interphase boundaries during solidification. This adsorbed layer acts as a barrier to the carbon flow necessary for the direct γ → α + Graphite and Fe₃C → α + Graphite reactions. With the graphite phase dis-abled as a sink for the excess carbon, the metal transforms like a nongraphitic steel. The effects of Mn, Sn, and Sb on the eutectoid transformation of ductile iron were shown to be consistent with their behavior in malleable iron.     

The electron metallography of ordering reactions in Fe-Al alloys

The microstructural changes during the α→ FeAl, FeAl → Fe₃Al, and α→ Fe₃Al transitions were studied by transmission electron microscopy. The ordering of ferromagnetic α was observed to occur in a classical manner by the nucleation and growth of particles of the FeAl or Fe₃Al type phases. However, the ordering of paramagnetic α to FeAl and paramagnetic FeAl to Fe₃Al occurred by a mechanism which showed many of the characteristics expected of a second or higher degree transition. These included critical point fluctuations in the degree of long-range order which also appeared to be greater in the vicinity of antiphase domain boundaries. The FeAl phase was also observed to partially disorder in the initial stages of the FeAl → α + FeAl transition and this effect appears to account for the anomalous magnetic behavior of some FeAl alloys.     

Martensitic phase transformations in IMI 550 (Ti-4Al-4Mo-2Sn-0.5 Si)

The influence of solution-treatment temperature on the martensitic phase transformations observed in IMI 550 (Ti-4Al-4Mo-2Sn-0.5Si) has been investigated. When solution treatment is conducted at temperatures above 1233 K, a hexagonal martensite (α′) is formed on rapid cooling. However solution treatment at temperatures between 1233 and 1123 K results in the formation of an orthorhombic martensite (α″) on rapid cooling. Finally, below 1123 K, the β phase is stable—no martensitic transformation occurs on rapid cooling. This transition from α′ → α _primary + (α′ + β _retained) → α _primary + (α″ + β _retained) → α _primary + β _metastable + ω, with decreasing solution-treatment temperature, is shown to be a result of alloy partitioning during solution treatment. Crystallographic analysis indicates that the transition in the martensite crystal structure with decreasing solution-treatment temperature is related to chemical short-range ordering (CSRO) in the high-temperature β phase.     

Thermodynamic consideration of formation mechanism of α1 plate in βCu-base alloys

For the possible ordering structures of the parent phase β′—i.e., B2 in Cu-Zn alloys, DO₃ in Cu-Al alloys, and B2 and L2, in Cu-Zn-Al alloys—the driving forces for the a, plate formation have been calculated for the three βCu-base alloys. The driving force, ΔG, is larger than zero for the β′ →α₁ shear mechanism and less than zero for the β′ → β′₁ + α₁ diffusional mechanism. Furthermore, the equilibrium temperature, T_o, between the parent β′ phase and the α in, plate has been evaluated to be much less than the experimental start temperature, B_s, of the α₁ plate formation. Therefore, the a! plate formation cannot be initiated by a diffusionless β′ → α₁ shear reaction without other causative factors such as stress field, defects, etc. However, the α₁ plate can be formed through a diffusional β′ → β′₁ +α₁ reaction. Results in Cu-Al alloys also show that the composition of the α₁ plate produced in the diffusional reaction has to deviate from that of the parent phase to a certain extent. For some compositions of Cu-Zn-Al alloys, ΔG^{α1(dis.)→α1(ord.)} < 0 within a temperature range. Thus, the fresh α₁, plate produced after the diffusional reaction may further transform into the ordered α₁ plate within this temperature range. Calculated driving forces for the disordered parent phase reveal that the ordering of the parent phase resists the α₁ formation in Cu-Zn and Cu-Zn-Al alloys and enhances it in Cu-Al alloys. This article is based on a presentation made at the Pacific Rim Conference on the “Roles of Shear and Diffusion in the Formation of Plate-Shaped Transformation Products,” held December 18–22, 1992, in Kona, Hawaii, under the auspices of ASM INTERNATIONAL’S Phase Transformations Committee.     

Bragg–Williams Model of CsCl-Type Ordering of the FeCo System in Strong Magnetic Fields

A modified Bragg–Williams (B–W) model of α and α′ FeCo is extended to estimate the effect of strong magnetic fields on the critical ordering temperature (T _ORDER) taking into account long-range chemical and magnetic ordering. The model discussed here is generalized from our previous work in which only the larger average exchange per atom in the chemically ordered state was taken into account. A positive shift of critical temperatures for the higher order α→α′ order-disorder phase transformation has been predicted in the presence of a strong field. In this work, the experimentally observed dependence of the average magnetic moment of Fe atoms on the degree of chemical order has been accounted for explicitly. The estimated shift in the critical ordering temperature (ΔT _ORDER) is larger when the dependence of the Fe moment on the degree of chemical order is taken into account, particularly in the case of Fe-rich compositions (e.g., ΔT _ORDER ∼ 13 K vs ΔT _ORDER ∼ 10 K for H ∼ 50 T at equiatomic composition). For most compositions, however, the contribution to ΔT _ORDER associated with the larger average exchange per atom in the chemically ordered state accounts for the majority of the shift. The estimated effect remains quite small and is only expected to be experimentally observable in static fields larger than currently available in most laboratories (ΔT _ORDER is only predicted to be larger than ∼2 to 3 K for H > ∼10 T). This article is based on a presentation made in the symposium entitled “Phase Transformations in Magnetic Materials”, which occured during the TMS Annual Meeting, March 12–16, 2006, in San Antonio, Texas, under the auspices of the Joint TMS–MPMD and ASMI–MSCTS Phase Transformations Committee.     

Effect of Si addition on the microstructure of an Fe-8.0AI-29.0Mn-0.90C alloy

The microstructures of two alloys with Fe-8.0Al-29.0Mn-0.90C, one without Si and one with 1.5 wt pct Si, have been investigated by means of transmission electron microscopy (TEM). In the as-quenched condition, the alloy without Si is single-phase austenite; however, some discrete particles along the austenite grain boundaries can be observed in the Si-bearing alloy. The discrete particles have a mixture of (α + D0₃) phases, indicating that the Si addition enhances the formation of (α + D0₃) phases. This result is in disagreement with those reported by other research on Fe-Al-Mn-Si-C alloys. Transmission electron microscopy examinations reveal that the (α + D0₃) phases are formed by an ordering transition during quenching. When the quenched specimen is aged at temperatures ranging from 450 °C to 1050 °C, the phase transformation sequence occurring within the (α + D0₃) region as the temperature increases is found to be D0₃→ (D0₃ +K phase) → B2 → α.     

Reduction of tungsten oxide to tungsten metal

Tungsten oxide, WO_2.96, was reduced toα-W in hydrogen for various time periods over the temperature range 500°C to 900°C. Intermediate oxides were determined using X-ray diffraction analysis of the semireduced powders. Several dopant conditions were used, to find the effect on oxide structures and reaction kinetics of the usual dopants K, Si and Al. The scanning electron microscope was employed to determine the morphology of the crystallites at intermediate and final stages of reduction. This research was supported in part by the U.S. Energy Research and Development Administration, Contract E(11-1)-1198.     

Interactions in the LiPO3 — MoO3, NaPO3 — MoO3, and KPO3 — MoO3 systems

The MPO₃ — MoO₃ (M=Li, Na, K) pseudobinary systems have been examined by differential thermal analysis and x-ray phase analysis. The phase diagrams have been derived, and the temperatures and compositions of the eutectics have been determined. The compounds have been examined by x-ray phase analysis, infrared spectroscopy, and diffuse reflection spectroscopy. The conductivity and optical properties of the compounds MMoO₂(PO₄) (M=Li, Na, K) have been determined. The coordinates of the liquidus lines have been used to calculate the activities of the components in the MPO₃ — MoO₃ systems. Those activities show large negative deviations from ideal solutions. This indicates strong interaction between particles in the liquid state. Translated from Poroshkovaya Metallurgiya, Nos. 3–4(412), pp. 33–40, March–April, 2000.