X-ray studies on phase equilibria in {Tm, Lu} - W - B ternary systems at 1070 K

Isothermal sections at 1070 K have been constructed by x-ray diffraction applied to the phase diagrams in the Tm - W - B and Lu - W - B systems. The solubility of “WB₂” in TmB₂ is low, while that in LuB₂ attains 0.15 molar fraction (lattice parameters of the (Lu, W) B₂ phase with a limiting composition and having the AlB₂ structure a=0.31772(6), c=0.35804(9) nm). The distinct boride reported previously Tm₃WB₇ is confirmed (Er₃CrB₇ structure type). New ternary compounds have been identified and examined by powder method (DRON-3M diffractometer): TmWB₄ (space group Pbam, structure type YCrB₄, a=0.59989(2), b=1.15866(4), c=0.35821(1) nm, N_hkl=157, R=0.0796) and Lu₂WB₆ (Pbam, structure type Y₂ReB₆, a=0.91339(4), b=1.14865(5), c=0.35124(2) nm, N_hkl=408, R=0.0981). Translated from Poroshkovaya Metallurgiya, Nos. 5–6(413), pp. 43–48, May–June, 2000.     

Component interactions in {Y, Gd, Tm} - Mo - B ternary systems at 1270 K

X-ray structure analysis has been used to construct isothermal sections at 1270 K for the phase diagrams for the Y - Mo - B and Tm - Mo - B systems. The solubility of MoB₂ in YB₂ is low, while that in TmB₂ is not more than 0.05 molar fraction (lattice constants of the (Tm, Mo)B₂ phase with the AlB₂ structure and limiting composition a=0.3253(2), c=0.3678(4) nm). The existence of some previously known borides is confirmed. and the lattice parameters for some of them have been refined: YMoB₄ (space group Pbam, structure type YCrB₄, a=0.6038(1), b=1.1672(2), c=0.36170(7) nm), YMo₃B₇ (Pnma, own structure type), GdMoB₄ (Pbam, type YCrB₄, a=0.60531(6), b=1.1700(1), c=0.36355(6) nm), Tm₂MoB₆ (Pbam, type Y₂ReB₆), TmMo₂B₇ (Pnma, type YMo₃B₇). New ternary compounds have been identified: Y₃MoB₇ (Cmcm, type Er₃CrB₇, a=0.34775(2), b=1.59793(5), c=0.94757(2) nm), Gd₃MoB₇ (type Er₃CrB₇, a=0.3497(2), b=1.6157(6), c=0.9516(5) nm), and TmMoB₃ (P2₁/m, type ErMoB₃, a=0.6771(2), b=0.3142(1), c=0.5373(1), β=101.48(2)°). The parameters of the metal atoms and their isotropic temperature factors have been refined for Y₃MoB₇ (DRON-3M diffractometer, N_hkl=288, R=0.106). Translated from Poroshkovaya Metallurgiya, Nos, 1–2(411), pp. 56–62, January–February, 2000.     

Reaction of Tungsten with Melts in the Cu - Co System

We have studied the solubility at 1200°C of tungsten in Cu - Co melts and the growth kinetics of a W₆Co₇ layer at the tungsten — melt interface. We have established the composition of the melt in the three-phase equilibrium tungsten — W₆Co₇ — melt: 0.0195 Co, 4.8 · 10⁻⁵ W, the rest is Cu (in atomic fractions). In the studied composition range for the melt, the solubility of tungsten is described well by the expression: lgX_W = −7.117 + 25.7 · X_Co ^1/2 − 41.06 · X_Co, where X_W and X_Co are the atomic fractions of the corresponding elements in the melt. We have determined the correlation between the growth rate for a layer of tungsten-containing phase at the tungsten — melt interface and the thermodynamic characteristics of the melt. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(443), pp. 81–86, May–June, 2005.     

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.     

A new phase in an Fe-9.0AI-29.5Mn-1.2Si alloy

A new type of precipitate (designated L phase) was observed within the ferrite matrix in an Fe-9.0Al-29.5Mn-l.2Si alloy after being aged at 550 °C. Transmission electron microscopy examinations indicated that the L-phase precipitate has a monoclinic structure with lattice parametersa = 0.656 nm,b = 0.797 nm,c = 0.637 nm, and β = 109.4 deg, and the orientation relationship between the L-phase precipitate and the ferrite matrix could be stated as follows: (-101)_α//(001)_L-phase (-110)_α//(-111)_L-phase with a deviation of 0.3 deg (01l)_α//(131)_L-phase with a deviation of 1.5 deg The L phase has never been observed in various Fe-Al-Mn, Fe-Mn-Si, Fe-Al-Si, and Mn-Al-Si alloy systems before.     

Production of high-strength tubes made of steels of type 15GFB

A unit for making L-class high-strength pump-compressor tubing composed of low-carbon, low-alloy steels of type 15GFB is now being used on the 140 mill in the tube-rolling shop at the Rustavi Metallurgical Plant. The steel 15GFB pump-compressor tubing made by the technology that was developed has the following service properties: σ_y = 630–670 N/mm², σ_u = 730–780 N/mm², δ = 18–22%, ψ = 55–60%, KCU = 1.6–2.2 MJ/m². The percentage of ductile fracture at room temperature is 85–95%. __________ Translated from Metallurg, No. 1, pp. 79–80, January, 2006.     

Effect of process parameters in the decomposition of a cryochemical salt product of the Bi - Pb - Sr - Ca - Cu - O system on the structure and properties of a ceramics

A study was made of the effect of the temperature and time of decomposition of a salt product on the phase composition, microstructure, and magnetic susceptibility of a Bi - Pb - Sr -Ca - Cu - O superconducting ceramics. Holding the powder at 570°C slows the formation of the high-temperature phases, while increasing the decomposition temperature to 840°C and increasing the time of decomposition at 815°C have the same effect on the concentrations of the phases Ca₂PbO₄, CuO, and (CaSr)₂CuO₃. The data obtained on magnetic susceptibility, together with the results of microscopic and x-ray spectral studies, made it possible to evaluate the effect of the morphology of the grains and the grain boundaries on the superconductivity of the sintered specimens. Translated from Poroshkovaya Metallurgiya, Nos. 5–6(413), pp. 91–100, May–June, 2000.     

Structure and phase formation of nanostructural ion-plasma Ti-Cr-Al-N coatings on a hard-alloy cutting tool

A The possibility to of fabricate fabricating nanostructural Ti-Al-Cr-N coatings on a cutting hard-alloy tool with crystallites 20–60 nm in size by the method of ion-plasma arc deposition with the use of a tree-cathode system for sputtering materials and the separation of plasma flows from a drop phase is shown. The dependences of that structure and phase formation in the coating material have on the accelerating bias potential (U = −100 to −160 V) supplied to a the substrate and determining the energy of sputtered particles and condensation temperature, as well as on a the current (I _Cr = 90–130 A) of a the sputtering arc at a the chromium cathode and the chromium concentration that depending depends on the the current within the vapor phase and the formed coating, are determined.     

Effect of structure on the fatigue strength of dispersion-hardened Ni - 20% Cr - Al2O3 condensed materials

The effect of the mean free path between particles A and the average grain size D, and also the duration of cyclic loading N in the range (0.2–5)·10⁷ cycles, on the fatigue limit of dispersion-hardened Ni - 20% Cr -Al₂O₃ condensed materials is studied on the basis of fatigue curves. With a correlation coefficient of more than 0.9 these dependences on A^−1/2 and D^−1/2 correspond to an equation of the Mott—Stroh type. It is shown that particle boundaries affect the cyclic strength of the materials to a greater extent than grain boundaries up to a concentration of 1.1%. A change in the fracture mechanism occurs with a correlation coefficient of less than 0.9. Translated from Poroshkovaya Metallurgiya, Nos. 1–2(411), pp. 112–120, January–February, 2000.     

Kinetics and Mechanism of High-Temperature Oxidation in Air of Au - Cu Alloy

We have used thermogravimetry to study the kinetics of high-temperature (up to 800 °C) oxidation of the alloy 58.3 mass% Au - 41.7 mass% Cu with isothermal heating of the specimens. Using petrographic analysis of the oxide layers, we determined the reaction products. We have shown that up to 200 °C, the indicated alloy is not oxidized at all. More rapid oxidation of the alloy is observed at temperatures above 400 °C. Up to 500 °C, an inner layer consisting of Cu₂O predominates in the two-layer scale on the alloy, while the outer CuO layer has a significantly smaller thickness. At 600 °C, the upper layer of scale contains Cu₂O while the lower layer contains Cu₂O and gold. At higher temperatures, all the way up to 800 °C, the scale is two-layer as before but its upper layer contains CuO while its lower layer contains Cu₂O and small gold rods distributed in that oxide. Thus we have established three oxidation regions characterized by different scale phase compositions and different mechanisms for the process, mainly due to transition from an ordered state of the alloy (intermetallic AuCu₃) to a completely disordered solid solution of gold in copper. We used the Arrhenius equation to calculate the apparent activation energy for oxidation: E₁ = 20.4 kJ/mole for the temperature range 400–500 °C and E₂ = 9.5 kJ/mole for 600–800 °C. __________ Translated from Poroshkovaya Metallurgiya, Nos. 7–8(444), pp. 85–91, July–August, 2005.     

Phase stability investigations of the palladium-cadmium system: part ii. structural studies

The crystal structure and the precise lattice parameters of palladium-cadmium alloys containing 33 to 60 at. pct Cd were determined by X-ray diffraction at 294 K, using samples quenched from 1073 K. The results indicate that at 1073 K the β₁(Ll₀) phase extends from 33 to 55 at. pct Cd while the β′(B2) phase is stable from 56 to 60 at. pct Cd. No evidence for the existence of a separate high-temperature phase between the β, and β′ phase fields was found. A modification of the currently accepted Pd-Cd phase diagram near the equiatomic composition is proposed. The lattice parameters of the fct β₁ - phase have the following values at the stoichiometric composition:a = 0.4 2817 nm,c = 0.3 6310 nm. The molar volume of the β₁-phase is a linear function of composition from 33 to 50 at. pct Cd. The partial molar volumes of Pd and Cd have the following values in this range: V_Pd = 8.87 cm³/g-atom, V_Cd = 11.18 cm³/g-atom. An analysis of Pd-and Pt-based Ll₀ phases indicates that the c/a ratio of these phases is related to their enthalpy of formation. Phases with a small enthalpy of formation have a high c/a ratio while phases with a large enthalpy of formation exhibit a small c/a ratio. Y. A. CHANG, formerly Professor of Materials Engineering and Associate Dean for Research, Graduate School, University of Wisconsin-Milwaukee     

Nanostructured Ti-Cr-B-N and Ti-Cr-Si-C-N coatings for hard-alloy cutting tools

Nanostructured Ti-Cr-B-N and Ti-Cr-Si-C-N coatings with various contents of chromium and nitrogen are obtained by the magnetron sputtering of multiphase composite targets. Their structure and phase composition are investigated by X-ray phase analysis, transmission and scanning electron microscopy, X-ray photoelectron spectroscopy, and optical emission glow-discharge spectroscopy. The Ti-Cr-B-N and Ti-Cr-Si-C-N coatings are based on the fcc phase with texture (100) and crystallite size <25 nm. The Si₃N₄-based hexagonal phase was also revealed in the Ti-Cr-Si-C-N coatings. An investigation into the properties of coatings with the use of methods of nanoindentation, scratch testing, and by performing tribological tests showed that they have a hardness of up to 30 GPa, an adhesion strength no lower than 35 N, and their friction coefficient falls in the range of 0.35–0.57. Coatings also possess high thermal stability, resistance to oxidation, and corrosion stability in a 1N H₂SO₄ solution. The data obtained in tests of hard-alloy cutting tools indicate that the deposition of nanostructured Ti-Cr-B-N and Ti-Cr-Si-C-N coatings increases its resistance by a factor of 11–17.     

Formation and stability of a nitride with the structure of beta manganese in Ni-Cr-N ternary system

A nitride with the metal-atom arrangement of β manganese, which is designated as π phase, was confirmed to exist as an equilibrium phase in the ternary Cr-Ni-N system. A Cr-40 mass pct Ni binary alloy was nitrided under a pure nitrogen atmosphere at 1523 K to prepare a Cr-40Ni-5N alloy consisting of a nickel-rich face-centered cubic (fcc) γ phase and a dichromium nitride, Cr₂N, designated as ε phase. Upon aging the alloy at 1273 K, the π phase was formed through a peritectoid reaction between the γ and ε phases. A volume fraction of the π phase reached 95 pct after 3.6 × 10⁵ s, and no more change of the volume fraction was observed, even after 3.6 × 10⁷ s aging. The chemical composition of the π phase was determined to be Cr₁₃Ni₇N₄, whose lattice parameter wasa = 0.6323 nm. The π phase became unstable above 1473 K, which explains a previous unsuccessful attempt to produce the Cr-Ni-N ternary π phase by the replacement of molybdenum in Mo₁₂Ni₈N₄ by chromium at 1473 K.     

Structural parameters of the low-temperature metastable form of the carbide W2C

A sufficiently complete spectrum of superstructure reflections was obtained by the x-ray diffraction analysis of a monocrystal to unequivocally determine, for the first time, the ordered structure of W₂C annealed for a long time at a temperature below that of its eutectoidal decomposition. It was shown that W₂C of eutectoidal composition in a metastable state has a rhombic ordered structure with the lattice parameters a=4.719 ± ± 0.003 nm × 10=c₀, b=6.017 ± 0.003 nm × 10 ≈ 2a₀, c=5.181 ± 0.003 nm × 10 ≈ √3a₀ (a₀, c₀ ≡ a_HCP, c_HCP). The specimens were obtained from tungsten alloys containing 30.5 and 35 at. % C, prepared by are melting followed by annealing at ∼2700°C (1 h) and stepwise cooling to 850°C (the total annealing time at temperatures below 1200°C was 538 h). Translated from Poroshkovaya Metallurgiya, Nos. 3/4(412), pp. 46–53, March–April, 2000.     

The (Cr) + (NbC) quasibinary eutectic in the Cr - Nb - C system

An experimental investigation of the Cr - Nb - C alloys has shown that in the (Cr) + (NbC) two-phase region there are the fold with maximal solidus temperature and the saddle point (Cr_79.5Nb_12.2C_8.3) on the liquidus surface, relating to L_c ⇔ (Cr) + (NbC) invariant equilibrium at ≥1640°C. Translated from Poroshkovaya Metallurgiya, Nos. 5–6(413), pp. 48–54, May–June, 2000.     

Oxidation of alloys of the system Ni−Ta. I. Oxidation of the intermetallic Ni3Ta

Oxidation kinetics for the intermetallic Ni₃Ta in air at 600–1000°C are studied by a thermogravimetric method. The alloy has an ordered crystal structure (D¹³ _2h-Pmmn) with rhombic lattice parameters a=0.512 nm, b=0.423 nm, and c=0.452 nm. The kinetic isotherms of Ni₃Ta oxidation are described by a parabolic equation. With t≤800°C there is a periodic increase in the rate constant of parabolic oxidation, but with t>800°C there is a periodic decrease of it. In the range 850–875°C the alloy oxidation rate decreases as a result of scale sintering. Oxygen diffusion slows down in the compact scale. X-ray and metallographic analysis of the scale that forms on Ni₃Ta indicates that it contains NiO, NiO·Ta₂O₅, Ta₂O₅ and also Ni and the solid solution Ni(Ta). These phase components are distributed in layers of the scale: NiO (first), NiO+NiO·Ta₂O₅ (second), NiO·Ta₂O₅+Ni+Ta₂O₅ (third), Ta₂O₅+Ni(Ta) (fourth). With a low temperature and short periods of heating there is no Nio·Ta₂O₅ or Ni(Ta) in the scale. Oxidation of Ni₃Ta is controlled by oxygen diffusion in the scale over the direction towards the alloy. With t>850°C this mechanism changes. By analogy with oxidation of tantalum it is assumed that structural changes in the Ta₂O₅ lattice may be responsible for this. Institute for Problems of Materials Science, Ukraine National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 3–4(406), pp. 80–87, March–April, 1999.     

Composition and structure of silicon oxycarbide fibers

The composition and structure of Si_xC_yO_z glassy fibers that form during carbonization of hydrated cellulose impregnated with silicon dioxide is studied by Auger-electron spectroscopy, chemical analysis, transmission and scanning electron microscopy. It is established that the surface layer of a fiber to a depth of 30 nm consists of oxycarbide phase SiC_1.1O_1.8 with chemically absorbed oxygen and nitrogen, but the inner layers are two-phase that apart from this phase contain amorphous carbon. __________ Translated from Poroshkovaya Metallurgiya, Nos. 7–8(450), pp. 7–9, July–August, 2006.     

Composite material based on nanocrystalline SiC reinforced with continuous SiC fibers

A paste of nanocrystalline particles was obtained by magnetron sputtering of a target consisting of silicon and graphite powders. The target and a silico-organic oil were evaporated together. Model specimens were fabricated from the paste and continuous SiC fibers. Interaction between the fibers and nanoparticles was investigated by measuring the internal friction of the model composite materials. It was found that sintering occurs in 16–20 h at 1473–1500 K for pastes containing nanoparticles with a diameter of =2–4 nm, and in 60–100 h for pastes with diameter =6–10 nm. The sinterng temperature is 230–270 K below the degradation temperature of the fibers. It was shown that it is possible to manufacture a composite material consisting of a nanocrystalline SiC matric reinforced with continuous SiC fibers. The bend strength of the composite was σ _B = (73 ± 9)·10⁷ Pat at 1500 K, and (64±12)·10⁷ Pa after thermal cycling at 1500 K for 100 h. Materials Science Institute, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 5/6(395), pp. 69–75, May–June, 1997.     

The thermal capacity and enthalpy of gadolinium sesquiselenide over a wide temperature range

Measurements have been made on the thermal capacity of γ-Gd₂Se₃ at 58.88–298.34 K. Values have been obtained for the thermal capacity, entropy, reduced Gibbs energy, and enthalpy under standard conditions: C°_p = 125.87 ± 0.5 J· mole⁻¹ · K⁻¹; S°(298.15 K) = 196.5 · 1.6 J · mole⁻¹ · K⁻¹; Φ°(298.15 K) = 103.6 ± 1.6 J · mole⁻¹ · K⁻¹; H°(298.15 K)-H°(0) = 27681 ± 138 J · mole⁻¹. The enthalpy of Gd₂Se₃ has been measured and the major thermodynamic functions have been calculated for the solid and liquid states over the temperature range 450–2300 K. The temperature dependence of the enthalpy in the ranges 300–1800 K and 2000–2300 K are represented: H°(T)-H°(298.15 K) = = 1.1949 · 10⁻² · T² + 122.38 · T + 347402 · T⁻¹ − 38716 and H°(T)-H°(298.15 K) = 262.81 · T-− 196047, respectively. The calculated temperature, enthalpy, and entropy of melting for Gd₂Se₃ are: T_m = 1925 ± 40 K, Δ_mH° (Gd₂Se₃) = 68.5 kJ · mole^-1, Δ_mS°(Gd₂Se₃) = 35.6 J · mole⁻¹ · K⁻¹. __________ Translated from Poroshkovaya Metallurgiya, Nos. 3–4(448), pp. 56–61, March–April, 2006.     

Discussion of “effects of tensile stress on microstructural change of eutectoid Zn-AI alloy”

In a recent contribution,[1] Zhu and Orozco presented a phase transformation of the ternary alloy Zn-20.2 wt pct Al-1.8 wt pct Cu, studied under tensile stress by using X-ray diffraction and scanning electron microscopy techniques. The authors report the existence of three phases in the alloy at room temperature after furnace cooling,α,ε, and a newη _′ ^T instead of the zinc-rich solid solutionη, as appears in the phase diagrams. The reported parameters for this hcp metastable phase are^[1,2] a = 0.2663 andc = 0.4873 nm; these values are close to the parameters of pure zinc,^[3] witha = 0.2664 nm andc = 0.4946 nm. The difference betweenη _′ ^T and zinc in thea parameter is around 0.03 pct, and it is 1.47 pet for thec parameter. When zinc is saturated with aluminum in the Zn-AI alloys, thea parameter shrinks^[3] to 0.2660 nm. It is possible to see that the value ofa of theη _′ ^T phase lies in-between the values of pure zinc and zinc-aluminum solid solution. The solubility of Al and Cu in Zn^[4] at 100 °C is 0.3 wt pct Cu and 0.06 wt pct Al. The covalent radius of Cu (0.117 nm) is smaller than the covalent radius of Al (0.118 nm) and Zn (0.125 nm), so the introduction of Cu in the zinc structure can result in a reduction of thec parameter. These values suggest that the metastable phaseη _′ ^T could be the hcp zincrich solid solution with low aluminum and copper contents. The article of Zhu and Goodwin,^[5] cited by Zhu and Orozco in their Reference 14, is related not to the eutectoid alloy, as they argue, but to an alloy with 27 wt pct Al, and no reports about the transformation ofε intoT′ were found. The presence of the metastable e phase (CuZn₄, sometimes called CuZn₅) at room temperature and its transformation to the stable phaseT′ (rhombohedral intermetallic phase, Al₄Cu₃Zn) have been observed by other authors.^[6,7] Y.H. ZHU and E. OROZCO:Metall Mater. Trans. A, 1995, vol. 26A, pp. 2611-15.