Solubility of oxygen in Fe–Co melts containing titanium

Solutions of oxygen in Fe–Co melts containing titanium are subjected to thermodynamic analysis. The first step is to determine the equilibrium reaction constants of titanium and oxygen, the activity coefficients at infinite dilution, and the interaction parameters in melts of different composition at 1873 K. With increase in cobalt content, the equilibrium reaction constants of titanium and oxygen decline from iron (logK(FeO · TiO₂) =–7.194; logK(TiO₂) =–6.125; logK(Ti₃O₅) =–16.793; logK(Ti₂O₃) =–10.224) to cobalt (logK(CoO · TiO₂) =–8.580; logK(TiO₅) =–7.625; logK(Ti₃O₅) =–20.073; logK(Ti₂O₃) =–12.005). The titanium concentrations at the equilibrium points between the oxide phases (Fe, Co)O · TiO₂, TiO₂, Ti₃O₅, and Ti₂O₃ are determined. The titanium content at the equilibrium point (Fe, Co)O · TiO₂ ? TiO₂ decreases from 1.0 × 10^–4% Ti in iron to 1.9 × 10^–6% Ti in cobalt. The titanium content at the equilibrium point TiO₂?Ti₃O₅ increases from 0.0011% Ti in iron to 0.0095% Ti in cobalt. The titanium content at the equilibrium point Ti₃O₅ ? Ti₂O₃ decreases from 0.181%Ti in iron to 1.570% Ti in cobalt. The solubility of oxygen in the given melts is calculated as a function of the cobalt and titanium content. The deoxidizing ability of titanium decline with increase in Co content to 20% and then rise at higher Co content. In iron and its alloys with 20% and 40% Co, the deoxidizing ability of titanium are practically the same. The solubility curves of oxygen in iron-cobalt melts containing titanium pass through a minimum, whose position shifts to lower Ti content with increase in the Co content. Further addition of titanium increases the oxygen content in the melt. With higher Co content in the melt, the oxygen content in the melt increases more sharply beyond the minimum, as further titanium is added.     

The use of PAP-2 aluminum powder to fabricate powder composites: Peculiarities of technology,structure, and physicomechanical properties of composites. Part 2. Study of composite properties and structure

The possibility of reinforcing the Al/Al₂O₃ laminated cermet matrix with metal rapidly solidified alloy fibers (steel, titanium, and aluminum), as well as discrete duralumin chips, is shown. The maximal reinforcing effect was attained when using titanium and steel fibers with their content of 20 and 10 vol %, respectively, due to the implementation of several energy-intensive destruction mechanisms. Reinforced composites are characterized by the following properties: ρ = 2.30–2.85 g/cm³, σ_bend = 180–250 MPa, K _1c = 7.5–15 MPa m^1/2, and KCU = (18–35) × 10³ J/m². The Al/Al₂O₃–C_coke.residue has ρ = 2.21–2.23 g/cm³ at a very low sliding friction coefficient of 0.17 (the counterbody is a ball made of steel ShKh-15 under a load of 1 N). The oxide-adhesion bond type, which makes it possible to remove spent grains from the grinding work zone and implement the self-sharpening mode, is formed for the “Al/Al₂O₃–fused alumina grains” composite. The material that contains kaolin fibers is ultra-light-weight ceramic insulation (0.25–0.5 g/cm³), λ = 0.07–0.2 W/(m K) in the 20–1000°C range. The material including alumina spherulites combines rather high hardness (σ_bend = 10–50 MPa) and porosity (42–52%) and has increased thermal stability due to the rapid elimination of the temperature gradient on structural elements having a micrometer-size cross section.     

Study of contact interaction between metalline borides and graphite at high temperatures in a vacuum

Summary We studied the contact interaction between compacted boride specimens and boride powders: TiB₂, ZrB₂, HfB₂, NbB₂, TaB₂, Mo₂B₅, and W₂B₅ and graphite powder and graphite at temperatures up to 2200°C in a vacuum. It was established by metallographic and chemical analyses together with microhardness test that the borides of hafnium, niobium, tantalum, and tungsten were stable in contact with graphite right up to 2200°C, and that molybdenum boride was stable up to its melting point, after a contact period of up to 5 h. In the case of titanium boride, we observed a slight interaction with graphite at 2200°, as a result of which the boride loses up to 1% boron, which transfers to the graphite charge. At 2200° after 5 h soaking, clear signs of interaction with graphite are detected in zirconium boride; during contact between compacted boride and graphite powder, the weight of the boride specimen and its microhardness decline, and traces of zirconium and boron are detected in the graphite charge. When compacted graphite is in contact with ZrB₂ powder, we observe a change in the chemical composition of the boride, an increase in the microhardness of the graphite, and a transition layer is detected on the contact boundary.     

Features of electrodeposition of “nickel-chromium diboride nanopowder” composite coatings

Conditions for obtaining a nickel-based composite electrochemical coating (CEC) with the use of the CrB₂ nanopowder as a strengthening phase in a standard nickel plating electrolyte are investigated. It is established that the nickel matrix is maximally saturated with the use of chromium nanoboride upon its concentration in the electrolyte of 5–10 kg/m³, which is lower by a factor of 8–12 than when adding CrB₂ micropowders. The microhardness of the CEC with the Ni-CrB_2(nano) composition with the content of the strengthening phase of 0.59–0.65% is higher than for the Ni-CrB_2(micro) coatings containing 2.47–2.86% boride by a factor of 1.16–1.19 and for the nickel host by a factor of 1.64–1.86. The optimal conditions of the CEC deposition are a cathode current density of 1.0 kA/m², a nanoboride concentration in the electrolyte of 5–10 kg/m³, pH = 5.0–5.5, and a temperature of 323 K.     

Influence of additives of silicon carbide and titanium diboride on the compaction during sintering and electrical resistivity of ceramical materials based on Al2O3

The effect of the sintering temperature on the density and electrical resistivity of Al₂O₃ based materials containing 30% TiB₂ (specimen A) or 30% SiC (specimen B) is studied. As the temperature rises in the range 1873–2023 K the relative density of the materials increases from 0.68 to 0.76 (A) and from 0.70 to 0.88 (B) the electrical resistivity decreases from 2.6·10⁴ to 2.9·10² Ω·cm (A) and from 7.4·10⁴ to 6.3·10² Ω·cm (B). The results can be used in the development of corundum-based ceramic heaters.     

Boriding of titanium OT4 from powder saturating media

The possibility of application of boriding media based on boron carbide—which additionally contain chromium, titanium, and silicon—for the diffusion hardening of titanium alloys is considered. Boriding in amorphous boron is performed for comparison. The microstructure, elemental composition, and phase composition of diffusion coatings on the OT4 titanium alloy formed by saturation in powder media are investigated. Hardening boride layers are formed on the titanium alloy form saturating media based on amorphous boron and multicomponent mixtures based on boron carbide. In all cases, the phase composition of the coating corresponds to phases TiB, Ti₂B₅, and Fe₂Ti. It is revealed that coatings from 30 to 150 μm thick are formed in conditions of the solid-phase saturation of titanium from powder mixtures due to the diffusion. Temperature-temporal conditions of formation of boride layers on OT4 titanium from powder saturating media are investigated and optimal modes for the formation of operable boride coatings are established. The optimal temperature range for processes of chemical-thermal boriding of titanium (900–1150°C) and saturation time (from 2.5 to 5 h) are determined. The maximal thickness of the operable boride coating on the OT4 titanium alloy is established, being from 180 μm in the case of saturation from B_amorph and up to 240 μm for the 50% B₄C + 20% SiC + 25% CrB₂ + 5% NaCl mixture at 950°C and saturation time of 4 h. Herewith, it should be noted that it was considered that the largest coating thickness is that retaining on the hardened sample surface.     

Anodic behavior of the NiO-Fe2O3-Cr2O3-Cu composite during the low-temperature electrolysis of aluminum

In order to fabricate oxide-metallic composites with the composition 25.3NiO-41.2Fe₂O₃-13.5Cr₂O₃-20.0Cu (wt %), the temperature and duration of sintering (1350°C, 30 min) that ensure the formation of the solid solution of chromium oxide in nickel ferrite have been determined. This material is tested as an anode for the electrolysis of the low-temperature solution with the composition 12.0NaF-36.8KF-51.2AlF₃ (wt %), which was saturated with Al₂O₃ (t = 800°C). The amount of gaseous oxygen evolved on the anode was measured. It is shown that the main reaction on an anode at current density i = 0.015–1.0 A cm^?2 is the oxidation of oxygen-containing anions from a melt with the formation of gaseous O₂ and a substantial increase in the oxidation rate of the composite anode is observed at i > 1.0 A cm^?2. The voltage across the electrolyzer (4.5 ± 0.5 V) and the anodic potential (2.43 ± 0.2 relative to the Al reference electrode) during a prolonged experiment (for 89 h, i = 0.4 A cm^?2) indicate a stable and acceptable electrical conductivity of the material, while the dissolution rate, which was calculated by the weight loss (0.6 kg/yr) and volume loss (0.7 cm/yr), satisfy the requirements to inert anodes.     

Synthesis of MoSi2-TiSi2 pseudobinary alloys by reactive sintering

MoSi₂-TiSi₂ pseudobinary alloys are synthesized from mixtures of elemental powders of molybdenum, silicon, and titanium by reactive sintering under a pseudoisostatic pressure of 150 MPa. When the titanium content in the alloy increases from 0 to 33 at. pct, the density of the alloy decreases from approximately 6 to 4 g/cm³, while the relative density is more than 95 pct independent of the titanium content. Vickers hardness of the alloy is approximately 800 when the alloy consists of a monophase structure of α-MoSi₂ or β-MoSi₂. However, the hardness increases to approximately 950 when the alloy consists of a dual-phase structure of (α-MoSi₂+β-MoSi₂) or (β-MoSi₂+γ-TiSi₂). The oxidation resistance of the alloy at 773 K is approximately tripled when the titanium content increases from 0 to 1.7 at. pct, but the effect of the titanium content on the oxidation resistance becomes less remarkable as the titanium content increases.     

Effect of composition and high energy rate forging on the onset of precipitation in an iron-base superalloy

The precipitation sequence in a modified A-286 Fe-base superalloy (nominally Fe + 30 pct Ni + 15 pct Cr + 2.0 pct Ti + 1.25 pct Mo + 0.2 pct Al) was examined by optical and electron microscopy and electrical resistance measurements. Secondary phases which precipitate during aging were found to be γ′ in the matrix; (Ti, Mo)C and a boride, M₃B₂, at grain boundaries; and 17 in three morphologies,i.e., cellular, Widmanstätten, and platelets inside γ′ particles. The exact aging sequence depends upon time, temperature, and pre-age condition. Composite time-temperature-precipitation (TTP) diagrams were developed which show the precipitation sequence for two pre-age conditions,viz., solution treated and high energy rate forged (HERFed). It was found that HERFing prior to aging accelerates γ′ and (Ti, Mo)C precipitation, whereas it has negligible effect on cellular 17 and M₃B₂ precipitation. HERFing also promotes the precipitation of Widmanstätten 17 and 17 platelets inside γ′ particles.     

Re-determination of the crystal structure of Ca2Y8Si6O26 and study on the luminescent properties of Ca2Y8Si6O26:Tb3+

The crystal structure of silicate oxyapatite Ca₂Y₈Si₆O₂₆ was indexed as hexagonal, space group P6₃/m, α=0.93515 nm, c=0.67872 nm, α=β=90°, γ=120°, V=0.5138692 nm³. Three strong peaks located at 32.079°, 32.595°, and 50.104° with d=2.7903, 2.74649, 1.8194 was in accordance with (211), (112), and (213) planes. The optimum concentration of Tb³⁺ in Ca₂Y₈Si₆O₂₆ to yield highest photoluminescence intensity was 10 mol.% of Y³⁺. The corresponding excitation spectrum consisted of an intense broad band from 220 to 260 nm. The photoluminescence measurements showed that the green emission originated from ⁵D₄?⁷F₅ was predominant in the measured range with strong doublet lines at 543 and 549 nm.     

Specific features of formation of nanostructured electrospark protective coatings on the OT4-1 titanium alloy with the use of electrode materials of the TiC-Ti<Subscript>3</Subscript>AlC<Subscript>2</Subscript> system disperse-strengthened by nanoparticles

The effect of nanodispersed additives of ZrO₂, Al₂O₃, NbC, W, WC, and WC-Co into the composition of the TiC-Ti₃AlC₂ electrode on the kinetics of formation of coatings by electrospark doping (ESD) on the titanium alloy of the OT4-1 grade on varying the duration of pulsed discharges in a wide range is investigated. The structure, phase composition, properties (continuity, thickness, microhardness, friction coefficient, wear resistance, and heat resistance) are investigated. The optimum energy mode of the ESD treatment of the OT4-1 titanium alloys by new electrode materials is determined. It is found that the introduction of a nanodispersed component is favorable to an increase in continuity and the microhardness of electrospark coatings and a substantial increase in wear resistance and heat resistance of titanium alloys.     

The effect of quality of anodes on the process of electrolytic of manganese dioxide

During the electrosynthesis of manganese dioxide, the anode material and anode current density (i _a) exert the largest influence on the characteristics of electrolysis and the quality of the obtained material. The activation of anodes, which consists of the deposition of the titanium-manganese alloy on the titanium base of the electrode by the thermal-diffusion method, prevents passivation at i _a = 100 and 200 A/m². The electrochemical characteristics of electrolysis for NTMA (a built-up titanium-manganese activated anode) and ATDP (an experimental activated anode with thermodiffusion coating) anodes at i _a = 100 and 200 A/m² have close values. The voltage across the bath does not exceed 2.2–3.0 V, the current efficiency is 95–98%, and electrical power consumption is 1.33–1.80 (kW h)/kg. The chemical composition and the crystalline modification of electrical manganese dioxide corresponds to the requirements of GOST (State Standard) 25823-83. The activated ATDP anodes behave similarly to the known HTMA anodes. After electrolysis, no variations in the surface layer are found on them.     

Electroerosion resistance and structural phase transformations in electrospark and laser deposition of titanium alloys using composite ceramics based on ZrB2-ZrSi2 and TiN-Cr3C2 systems

The paper examines the mass transfer kinetics, structure, phase and chemical compositions, and micromechanical properties of electrospark and laser coatings on titanium alloys (including their combination) deposited using composite materials based on the ZrB₂-ZrSi₂ and TiN-Cr₃C₂ systems. The electrospark deposition of both materials is characterized by a relatively high mass-transfer coefficient (∼40–60%) over a wide range of treatment time t ≥ 1 min/cm². It is determined that after prolonged electrospark deposition (t = 7 min/cm²), ZrB₂-ZrSi₂ coatings have structurally heterogeneous surface with smoothed Ti-alloy localities caused by the melt crystallization and modified with alloying components. It is shown that ZrB₂-based coatings are promising along with conventional wear-resistant coatings based on refractory titanium compounds. __________ Translated from Poroshkovaya Metallurgiya, Vol. 47, No. 1–2 (459), pp. 151–161, 2008.     

Microstructural Modification and property improvement of boride/Ti-6Al-4V surface-alloyed materials fabricated by high-energy electron-beam irradiation

The present study is concerned with the fabrication and microstructural analysis of boride/Ti-6Al-4V surface-alloyed materials using the irradiation of a high-energy electron beam. Mixtures of TiB₂ or MoB powders and CaF₂ flux were placed on a Ti-6Al-4V alloy substrate and subsequently irradiated using a high-energy electron beam. Specimens processed with a flux mixing ratio of 40 wt pct showed that the melted region of 1.1 to 1.5 mm in thickness was homogeneously formed without defects and contained a large amount of titanium borides (TiB). The formation of TiB in the melted region greatly improved the Vickers hardness, high-temperature Vickers hardness, and wear resistance to levels 2 or 3 three times higher than the those for the Ti alloy substrate. Also, the addition of MoB powders into the mixtures made possible the fabrication of surface-alloyed materials with various properties by controlling the kind, size, and volume fraction of TiB and the characteristics of the matrix. These findings suggested that surface alloying using high-energy electron-beam irradiation was economical and useful for the development of boride/Ti-6Al-4V surface-alloyed materials with improved properties.     

Studies on BaO-Y2O3-TiO2 Microwave Dielectric Ceramics

BaO-Y₂O₃-TiO₂ microwave dielectric ceramics with the rich area of TiO₂ were fabricated by a solid-state reaction method using BaCO₃, Y₂O₃, TiO₂ powders as starting materials. The sintering characteristics, phase composition, micro-structures and microwave dielectric properties of BaO-Y₂O₃-TiO₂ microwave dielectric ceramics with different k values sintered at different temperatures were investigated. The results showed that the sintering temperature of BaO-Y₂O₃-TiO₂ microwave dielectric ceramics was lower (about 1240 °C), and the sintered ceramics with the major phase of Y₂Ti₂O₇ had excellent dielectric properties. When k = 4, ɛ_r and tanδ were about 78.3 and 3 × 10⁻³ respectively. When k=5, ɛ_r and tanδ were about 53 and 9 × 10⁻⁴ respectively.     

Investigation into the Structure Formation and Properties of Materials in the Copper–Titanium Disilicide System

The structure formation and properties during infiltration, free sintering, and spark-plasma sintering in Cu–(12.5–37.5 vol %) powder materials Ti₃SiC₂ are investigated by electron microscopy, X-ray phase analysis, and energy-dispersion analysis. The independence of the phase composition of composite materials (CMs) on the sintering method and temperature in a range of 900–1200°C is established. The peculiarities of formation of the CM structure during sintering are the intercalation of silicon from titanium carbosilicide and the formation of a carbon solid solution based on Ti₅Si₃(C) titanium disilicide, small amounts of titanium carbide, silicon carbide, and TiSi₂ silicide. An increase in Ti₃SiC₂ in the CM certainly lowers electrical conductivity, but considerably increases the hardness, strength, and electroerosion wear resistance of CM electrodes for electroerosion broaching.     

Gradient Structure of the Layer Applied to Hardox 450 Steel by Fe–C–Cr–Nb–W Powder Wire after Electron-Beam Treatment

Surfacing with composite coatings strengthened by carbide, boride, and other particles is currently of great interest in materials physics. The performance of the applied layer is primarily determined by the phase composition of the coating. To permit the selection of coatings capable of withstanding extremal operating conditions, including high loads and abrasive wear, their properties and structure must be investigated in detail. In the present work, state-of-the-art techniques in materials physics are used to study the structure, phase composition, and tribological properties of coatings applied to Hardox 450 low-carbon martensitic steel by Fe–C–Cr–Nb–W powder wire and then subjected to electron-beam treatment. The electron-beam parameters are as follows: in the first stage, energy density per pulse E_S = 30 J/cm²; pulse length τ = 200 μs; and number of pulses N = 20; in the second stage, E_S = 30 J/cm²; τ = 50 μs; and N = 1. These conditions are selected on the basis of calculations of the temperature field formed in the surface layer of the material by a single pulse. It is found that electron-beam treatment of an applied layer of thickness about 5 mm leads to modification of a thin surface layer (about 20 μm), consisting largely of α iron and the carbide NbC; small quantities of the carbides Fe₃C and Me₆C (Fe₃W₃C) are also present. This modified surface layer differs from the unmodified coating mainly in terms of the morphology and dimensions of the secondary-phase inclusions. In the modified surface layer, the inclusions are smaller and take the form of thin layers along the grain boundaries. In the unmodified coating, the inclusions are mainly rounded particles, chaotically distributed within the grain. After electron-beam treatment, the wear resistance of the applied layer increases by a factor greater than 70 with respect to Hardox 450 steel, while the frictional coefficient is significantly less (about a third as much).     

Physical properties of the boride phases of chromium

Summary Certain physical properties (specific conductivity, thermal coefficient of electrical resistance, thermal conductivity, thermal, emf, Hall constant, melting point, microhardness) of the boride phases of chromium-Cr₄B, Cr₂B, CrB, Cr₃B₄ and CrB₂-were determined in this investigation.On the basis of the regular change in the physical properties of the phases with a change in the boron content, the conclusion is drawn that the nature of the chemical bond in the phases changes from the metallic for low boride phases to the covalent-metallic for higher phases.     

The crystal structures of Hf3N2 and Hf4N3

The crystal structures of ε-Hf₃N₂ and ζ-Hf₄N₃ were determined from X-ray powder photographs. The structure of both phases is trigonal, space group D ₅ ^3d -R?3m, with unit cells ofa _R = 7.972Å, α= 23 deg 12 min (hexagonal axes:a = 3.206Å,c = 23.26Å) for ε-H₃H₂, and a_R= 10.54Å, α = 17 deg 32 min (hexagonal axes:a = 3.214Å,c = 31.12Å) for ζ-Hf₄N₃. The nine close packed metal layers in ε-Hf₃N₂ are stacked according to (hhc)₃, or ABABCBCAC. The structure of ζ-Hf₄sN₃, isomorphous with ζ-V₄C₃,¹ consists of twelve close-packed metal layers in a stacking sequence (hhcc)₃. The nitrogen atoms occupy octahedral interstices in the metal lattice. The experimentally observed compositions, Hf₃N₁.₆₉ and Hf₄N₂.₅₆, shows both phases to be substantially deficient in nitrogen. ε-Hf₃N₂ is unstable above 2000°C, and ζ-Hf₄N₃ above 2300°C.