Kinetics of disilicide layer growth at the interface of tungsten with molten copper, silver, and tin saturated with silicon

The kinetics of WS₂ layer growth at the interface of tungsten with molten metals saturated with silicon is studied. Research is performed at 1200°C using melts based on copper, silver, and tin. It was established that WSi₂ layer growth in these melts obeys a “parabolic” rule but the corresponding growth rate constants differ markedly, i.e., from 3.4·10^?11 m²/sec (melt based on copper) to 1.5·10^?13 m²/sec (melts based on silver and tin). The reasons for this difference are discussed.     

Electrochemical synthesis of tetragonal oxide tungsten bronze nanofilms on platinum

We are the first to synthesize nanofilms of tetragonal oxide tungsten bronze (OTB) on a Pt(110) substrate by the electrolysis of the K₂WO₄–Na₂WO₄–WO₃ melt at 700 and 750°C. The composition and the morphology of OTB are shown to depend on the deposition potential and the WO₃ concentration in the melt. The laws of formation of tetragonal OTB films are discussed. The synthesized OTB samples are found to have a good thermal stability in the temperature range 20–800°C.     

Theory and technology of sintering processes,thermal and thermochemical treatment reaction kinetics for interaction of tungsten with copper-zirconium melts

We investigated the growth kinetics of layers of W₂Zr phase on tungsten interacting with copper-silicon melts at 1150°C. We determined the limiting value of the zirconium content in the copper melt (40.1 at. %). Below this value, we do not observe the indicated layer. We discuss the mechanism of reactive diffusion in the system and the effect of zirconium additives on the liquid phase sintering of the copper-tungsten materials. We have discovered well-defined differences between the growth rates of the layers on polycrystalline and single-crystal specimens of tungsten.Institute of Problems in Materials Science, National Academy of Sciences of Ukraine. Kiev. Translated from Poroshkovaya Metallurgiya. Nos. 3–4(384). pp. 25–29. March–April 1996. Original article submitted October 25, 1994.     

High-temperature electrometallurgical synthesis of tungsten and molybdenum carbides

Compositions of the products of the electrolysis of melts based on a eutectic mixture of sodium chloride-lithium fluoride and sodium tungstate, which contains molybdenum(VI) and tungsten(VI) oxides, molybdates, tungstates, and carbonates of lithium or sodium, are investigated. It is shown that, depending on the content of melt components, the products of electrolysis are carbon, molybdenum, tungsten, and their bronzes and carbides. The conditions of the deposition of galvanic coatings of molybdenum and tungsten carbides on carbon, nickel, and copper matrices are determined.     

Interaction of titanium boride with niobium and tungsten

Summary Results are presented of investigations of the nature of the interaction of titanium boride with niobium and with tungsten in powder mixtures sintered on heating to 2850°C for TiB₂-Nb and to 2700°C for TiB₂-W.     

Environmentally safe fluoride cycle in tungsten technology. Substantiation of the production cycle with fluorine and hydrogen recycle

A fluoride cycle in tungsten technology is based on three processes: (i) electrochemical decomposition of HF in the KHF₂ + HF melt at 80–100°C with the separate evolution of gaseous fluorine and hydrogen; (ii) fluorination of the tungsten powder with evoluated fluorine at 300–350°C with the condensation of formed WF₆ in a liquid form at t = 2.5–3.0°C, and (iii) reduction of gaseous WF₆ with evoluated hydrogen at t = 580–600°C with the condensation of formed HF at +1°C and its use for the fluorine and hydrogen production, thereby ensuring their recycling in the cycle. The optimization of mentioned processes resulted in hardware-process implementations providing the formation of a large-scale plane and cylindrical billets in the industrial scale for deformation, as well as pipes, crucibles, and other products of various sizes made of tungsten with productivity of one process line of ~4.3 kg/h (>34 t/yr) with the fulfillment of environmental requirements. In contrast with the methods of powder metallurgy, the described technology ensures the formation of dense half-finished products and products made of pure tungsten with finer grain structures and almost unlimited sizes. Herewith, the specific power consumption for 1 kg of production lowers by a factor of 2.0–2.5. To increase the production efficiency, the simultaneous operation of four process lines in an automated mode is recommended.     

Reactions of tungsten with copper-silicon liquids

A study has been made on the interaction of tungsten with silicon dissolved in liquid copper, which leads to the formation of a silicide layer. The measurements were made at 1200°C with silicon contents in the liquid up to 40 mass %. For silicon concentrations below 10 mass %, no silicide is formed at the tungsten-liquid interface. There is a discussion of the reaction thermodynamics. The results may be used to analyze the liquid-phase sintering of tungsten-copper and molybdenum-copper materials with added silicon.Institute of Materials Science Problems, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 3/4, pp. 29–32, March–April, 1995.     

Mechanism of fracture of dispersion-strenghthened tungsten

Conclusions In a dispersion-strengthened tungsten alloy fracture mechanisms change with rise in temperature in the same sequence as in unalloyed tungsten: quasibrittle cleavage at low temperatures is succeeded by partly tough fracture at 400°C (T _Br ^u1 ), tough fracture through the body of the grain is observed in the range from 1000 (T _Br ^u2 ) to 1600°C, and at 1800°C tough intergranular fracture commences. The cold-brittleness points of the dispersion-strengthened tungsten alloy are lower (T _Br ^u1 by 100 and T _Br ^u1 by 200°C) then those of unalloyed tungsten, while the temperature of transition to tough intergranular fracture is higher. As a result, the dispersion-strengthened alloy has a wider temperature range of tough transgranular fracture, with a larger value of. The wider range of tough transgranular fracture in the dispersion-strengthened tungsten alloy may be linked with a tendency for microvoids to form in the material on the second-phase particles, as a consequence of which subsequent fracture occurs by a microvoid coalescence mechanism.Translated from Poroshkovaya Metallurgiya, No. 7(283), pp. 31–35, July, 1986.     

Structural stability of super duplex stainless weld metals and its dependence on tungsten and copper

Three different superduplex stainless weld metals have been produced using manual metal arc welding under identical welding conditions. The concentration of the alloying elements tungsten and copper corresponded to the concentrations in commercial superduplex stainless steels (SDSS). Aging experiments in the temperature range 700 °C to 1110 °C showed that the formation of intermetallic phase was enhanced in tungsten-rich weld metal and also dissolved at higher temperatures compared with tungsten-poor and tungsten-free weld metals. It could be inferred from time-temperature-transformation (TTT) and continuous-cooling-transformation (CCT) diagrams produced in the present investigation that the critical cooling rate to avoid 1 wt pct of intermetallic phase was 2 times faster for tungsten-rich weld metal. Microanalysis in combination with thermodynamic calculations showed that tungsten was accommodated in χ phase, thereby decreasing the free energy. Experimental evidence supports the view that the formation of intermetallic phase is enhanced in tungsten-rich weld metal, owing to easier nucleation of nonequilibrium χ phase compared with σ phase. The formation of secondary austenite (γ₂) during welding was modeled using the thermodynamic computer program Thermo-Calc. Satisfactory agreement between theory and practice was obtained. Thermo-Calc was capable of predicting observed lower concentrations of chromium and nitrogen in γ₂ compared with primary austenite. The volume fraction of γ₂ was found to be significantly higher in tungsten-rich and tungsten + copper containing weld metal. The results could be explained by a higher driving force for precipitation of γ₂ in these.     

Reactions at phase boundaries in pseudoalloys based on tungsten (molybdenum) and copper

Conclusions The reaction between tungsten and copper in the presence of nickel under conditions close to those of pseudoalloy formation is characterized by the formation of a two-layer zone in the copper. Next to the tungsten there is a layer of a phase containing W, Ni, and Cu. The reaction between molybdenum and copper under the same conditions is not accompanied by the formation of a new phase. It is possible to activate the reactions at the phase boundaries of such a pseudoalloy without increasing its electrical resistivity by decreasing the amount of nickel added to it and ensuring that the addition is evenly distributed over the surface of the particle of the pseudoalloy's refractory component. The addition of cobalt to a molybdenum-copper pseudoalloy leads to the appearance of layers of a Mo₆Co₇-base phase at its phase boundaries.Translated from Poroshkovaya Metallurgiya, No. 12(216), pp. 39–44, December, 1980.     

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.     

金属有机化学气相沉积W薄膜

以W(CO)6为前驱体,采用金属有机化学气相沉积法(MOCVD)在Cu基体表面进行了沉积W薄膜的研究.通过调整W(CO)6热解温度、W(CO)6气化温度及载气(高纯氢气)的流量等工艺参数,成功制备了均匀、致密的W薄膜;研究了沉积速率与上述参数之间的关系,并得出了在本试验条件下应用金属有机化学气相沉积法(MOCVD)制备...     

The solubility of tungsten in molten iron

The solubility of tungsten in iron has been determined at 1560–1620°C by successively saturating molten iron with tungsten while ensuring a uniform distribution of the content over the height. The temperature dependence of the solubility over that temperature range is described by a Schröder equation: C_s=(3.94±0.11)×10³e-(84.4±0.4)/RT.     

Coagulation of tungsten nanopowders under annealing in hydrogen

Coagulation of tungsten nanoparticles is investigated under annealing in hydrogen flow at 600–1000°C and duration of holding up to 1 h. It is established that the main mechanism of coagulation is the gasphase transport, and mass carriers are the WO₃ · H₂O molecules. Evaluative calculations of the coagulation rate are performed and their satisfactory agreement with experimental results is shown. Recommendations for optimization of conditions of thermal treatment of tungsten nanopowders are given.     

Interaction between vanadium carbide and aluminum and copper melts

The effect of low-frequency vibrations on the interaction between molten metals (Al,Cu) and vanadium carbide is studied. These vibrations are shown to initiate wetting of the V8C7 carbide by a copper melt and a chemical interaction in the Al-V8C7 system, resulting in the formation of vanadium aluminides and aluminum carbide.     

Phase transformations in reactive sintering of tungsten

Abstract

It has been demonstrated recently that tungsten (T _m = 3410±20°C) can be sintered by reactive sintering in a reductive atmosphere such as hydrogen. This alternative technique to the conventional sintering (T _s>2000°C) makes use of a small amount of aluminium addition which acts as a sintering aid and hence lowers the sintering temperature significantly (T _s1200°C). This study explores the phase transformations that take place during reactive sintering of tungsten in view of the mechanisms involved. DSC, SEM and TEM have been used for a fundamental understanding of this system.     

Catalytic effect of cobalt on the carburization kinetics of tungsten

The kinetics of the gas-phase carburization of tungsten by methane were studied and found to be controlled by two surface reactions and a later diffusion limiting reaction. The two surface reactions were found to produce the compounds W₂C and W₂C-WC respectively. The diffusion limiting reaction produced only WC. Extensive carburization caused cracking of the tungsten material. Cobalt was found to form a thin film on each tungsten surface which was easily converted to eta-phase (Co₃W₃C) when carburization began. A model was proposed and kinetic equations were developed which predict the rate of reaction for both cylinders and powders. The reaction rate curves for the uncatalyzed reaction using the same equations was also developed. CHARLES F. DAVIDSON, formerly with Fansteel Research Center, Salt Lake City, Utah     

Interaction of niobium and tungsten monocarbides in molten copper

The chemical interaction of uncompacted monocarbide NbC and WC powders, which were taken at mass carbide ratios NbC: WC = 10: 1, 3: 1, 1: 1, and 1: 3 and a total carbide content of 20 wt %, in molten copper is studied at 1300°C. The primary and secondary phase transformations that result in the appearance and decomposition of an (Nb,W)C solid solution are analyzed. The activating role of low-frequency vibration is shown.