Tungsten-rhenium Alloys Research Articles

CVD Tungsten and Tungsten-Rhenium Alloys for Structural Applications

Abstract The microstructures of CVD tungsten and tungsten-rhenium alloys have been investigated to evaluate their suitability as high temperature materials. We found that the partial pressure in the reaction chamber affected the microstructure and surface roughness of deposited pure tungsten and tungsten-rhenium alloys. Grain sizes smaller than 0.5 im were obtained for both deposited pure tungsten and tungsten-rhenium alloys. Fine-grained tungsten proved to have greater hardness (Hv>1000 at room temperature (R.T.)) bending strength (δ = 700-1230 MPa at R.T.-l 175 K) and thermal coefficient of linear expansion (β = 4.5-4.9 xl06K−1 at 575-1175 K) characteristics than tungsten with columnar structure.

Hafnium carbide growth behavior and its relationship to the dispersion hardening in tungsten at high temperatures

The growth behavior of hafnium dispersed carbide particles and its relationship the strength of a tungsten-rhenium alloy at temperatures above 2200 K have been examined with transmission electron microscopy. From 2200 to 2600 K, HfC particles grow homogeneously with a relatively slow growth rate. In this temperature region, the activation energy for HfC particle growth is determined to be 50.2 ± 1.0 kcal mol −1. The coarsening of HfC particles is a bulk diffusion-controlled process and hafnium is the less stable element in the HfC decomposition and growth process. Rapid particle growth occurs at temperatures above 2600 K. A bi-modal particle size distribution is observed at 2800 and 3000 K and selective particle growth takes place along dislocation lines and at grain boundaries, indicating that dislocation and boundary enhanced diffusion mechanisms are involved in the HfC particle coarsening process above 2600 K. Based upon the studies on the growth behavior of HfC particles, An Ashby-Orowan dispersion strengthening model is applied to the HfC hardened tungsten. Good agreement is obtained between the calculated resolved shear stress and experimental results.

Preliminary evaluation of tensile and stress-rupture behavior of W + 24 At. Pct Re + 0.4 At. Pct HfC wire

The tensile properties of hafnium carbide-dispersed tungsten-rhenium alloy wire, W + 24 at. pct Re + 0.4 at. pct HfC (W24ReHfC), were studied from liquid nitrogen temperature (LN2) to 1750 K and its stress-rupture behavior determined from 1144 to 1500 K. These results are compared to previous data on W + 4 at. pct Re + 0.4 at. pct HfC (W4ReHfC) and W + 0.4 at. pct HfC (WHfC) wire.[5] The room-temperature (RT) tensile strength of the W24ReHfC wire was about 3250 MPa and higher than that of the W4ReHfC (3160 MPa) and WHfC (2250 MPa) wires. The RT ductility of the W24ReHfC wire was quite high with a 50 pct reduction of area, whereas the W4ReHfC wire and the WHfC wire had RT ductilities of 28 and 2 pct, respectively. At temperatures of 1144 to 1366 K, the W24ReHfC wire had tensile strengths favorably comparable to the W4ReHfC and WHfC wires. However, above 1366 K, the W4ReHfC wire had both a greater tensile strength and stress-rupture strength than the W24ReHfC wire. The main contributions to the strengthening of the W24ReHfC wire were the fine and elongated fibrous grain microstructures and the dispersion of the HfC particles in the W-Re matrix. These properties suggested that the W24ReHfC wires hold promise as potential fiber reinforcements in composites from RT to about 1350 K.

High-temperature spectral emissivity of several refractory elements and alloys

Thermionic energy conversion has emerged as the method of choice for the direct space-based conversion of heat to electricity. An important parameter in the implementation of this method of direct energy conversion is the emissivity of the converter emitter and collector materials. This information is necessary to determine heat losses, heat transfer, and reservoir temperatures in the thermionic energy converter. Spectral normal emissivities were acquired at a wavelength of 0.65 ώm for a series of tungsten-rhenium alloys, tungsten-osmium alloys, and tungsten-iridium alloys in the temperature range 1400 to 2600 K. Additionally, the spectral normal emissivity for pure elements of molybdenum and ruthenium were obtained over the temperature range 1200 to 2600 K and 1400 to 2250 K, respectively. The spectral normal emissivities for a niobium-67% ruthenium (eutectic composition) in the temperature range 1400 to 2000 K were also obtained at the same wavelength. In all cases, the emissivity decreased linearly with increasing temperature. Both the tungsten-osmium and the tungsten-rhenium alloys exhibited emissivity values of 0.32 to 0.54 over the temperatures tested. The tungsten-iridium alloy yielded emissivity data of 0.35 to 0.47. The niobium-ruthenium emissivity data were within 0.34 and 0.36. The pure molybdenum and pure ruthenium experiments resulted in emissivity values ranging from 0.35 to 0.45 and 0.35 to 0.39, respectively.

Ultrahigh temperature tensile properties of arc-melted tungsten and tungsten-iridium alloys

Tungsten is one of the most important metals for high temperature applications. The major deterrents to the use of tungsten are poor fabricability at room temperature and rapid decrease in strength at temperatures above 1600 K. Previous investigations have shown that the addition of rhenium to tungsten improves both room- temperature fabricability and high-temperature strength. Based on its similarity to rhenium's electron structure, iridium as another potential alloying element in tungsten. It was recently confirmed that tungsten-iridium alloys with less than 1.0w/o iridium exhibit better fabricability than tungsten-rhenium alloys at room temperature. The strength properties of tungsten-iridium alloys at ultrahigh temperatures have not yet been researched. The present paper reports the tensile properties of dilute tungsten-iridium alloys in the temperature range 1600 to 2600 K. The focus of the present paper is to examine the effects of iridium concentration and test temperature on the strength and fracture behavior of tungsten-iridium alloys at ultrahigh temperatures.

Ｗ‐Ｒｅ合金の高温破壊じん性

Fracture toughness tests of tungsten and tungsten-rhenium alloy were carried out at elevated temperatures. The effect of rhenium content on fracture toughness and the temperature dependence of fracture toughness were investigated. Fracture surface were observed in detail. Although the fracture toughnesses of three kinds of materials with rhenium of 0, 5 and 10wt% were almost identical at room temperature, the materials with higher rhenium content had the higher fracture toughness at elevated temperatures. The brittle-ductile transition similar to that of steels and the ductile-brittle transition at which recrystallization occurred, were observed for all three kinds of materials. With an increase of rhenium content, the brittle-ductile transition temperature decreased and the ductile-brittle transition temperature increased. A significant grain growth in the temperature range higher than the recrystallizing temperature, which was observed in the tungsten material without rhenium, was not found in the tungsten-rhenium alloy materials.

Engineering design of the TITAN-II divertor

The design of the toroidal-field divertor for the TITAN-II reversed-field-pinch reactor is described. Strong radiation from the core and edge plasma spreads the heat load over the first wall and divertor areas of the high-power-density reactor, and careful shaping of the divertor target plate restricts the maximum heat flux to ~7.5 MW/m 2 . A further feature leading to manageable heat fluxes is the “open” configuration for the divertor, in which the target plate is located close to the null point to take advantage of the expansion of magnetic flux. The divertor target is constructed from a single material, a tungsten-rhenium alloy, for both the armor and coolant tubes, to avoid stress concentrations which arise at the interface between different materials. This alloy was chosen for its high ductility and good thermal and mechanical properties, which are retained at high temperatures, and for its excellent resistance to erosion by sputtering in the anticipated divertor plasma conditions. Detailed finite-element modeling of the divertor target indicates a peak equivalent thermal stress in the armor of ~500 MPa. Fabrication of the divertor plate is based on brazing the bank of coolant tubes to the armor, all components being manufactured using powder metallurgy techniques. The coolant for the divertor plate ia an aqueous LiNO 3 solution, with a lithium atomic percentage of 6.4%, as used throughout the fusion power core. Consideration of the thermal and physical properties of this solution allows coolant conditions to be chosen such that an adequate safety margin for critical heat flux is provided.

Material selection for the titan reversed-field pinch reactor

The operating conditions of a compact, high neutron wall loading fusion reactor severely limit the choices for structural, shield, insulator and breeder materials. In particular, the response of plasma-facing materials to radiation, thermal and pressure stresses, and their compatibility with coolants are of primary concern. Material selection issues were investigated for the compact, high mass power density TITAN reactor design study. In this paper the major findings regarding material performance are summarized. The retention of mechanical strength at relatively high temperatures, low thermal stresses, and compatibility with liquid lithium make vanadium-based alloys a promising material for structural components. The thermal creep behavior of V-3Ti-1Si and V-15Cr-5Ti alloys has been approximated. In addition, irradiation behavior including the effects of helium generation and coolant compatibility issues were investigated which led to the choice of V-3Ti-1Si as the primary structural material candidate for the liquid-lithium-cooled TITAN-I. For the water-cooled TITAN-II reactor, ferritic alloys are favored among structural material candidates. Depending on the choice of lithium salt dissolved in water, the radiolytic effects and corrosion characteristics of the aqueous breeding solution may be severe. LiOH and LiNO 3 have been identified as the most viable salts; however, the radiolytic and corrosion behavior of these salts in aqueous solutions differ substantially. The radiolytic behavior of the aqueous salt solutions has been examined and various molecular decomposition product yields were estimated for the TITAN-II irradiation conditions. Insulator material issues of concern include irradiation induced swelling and radiation-induced conductivity. Both issues have been investigated and operating temperatures for minimum swelling and dielectric breakdown strength have been identified for spinel (MgO-Al 2 O 3 ). The high heat flux and sputtering/erosion issues limit the choice of the materials for the divertor target plate. Mechanical properties of various tungsten-rhenium alloys have been investigated. A highly ductile W-Re alloy containing 26 atomic percent rhenium was identified as a viable plasma-facing material.

Tungsten-rhenium alloys as diffusion barriers between aluminum and silicon: S E Hörnström et al, J Vac Sci Technol, A6, 1988, 1650–1655

Tungsten-rhenium alloys as diffusion barriers between aluminum and silicon: S E Hörnström et al, J Vac Sci Technol, A6, 1988, 1650–1655

Tungsten–rhenium alloys as diffusion barriers between aluminum and silicon

Tungsten–rhenium alloys have been investigated as possible diffusion barriers between aluminum and silicon for high-temperature metallization of microelectronic devices. Al/W–Re/Si structures with the alloy compositions W–30 wt. % Re, W–61 wt. % Re, and W–72 wt. % Re were prepared by electron beam evaporation of W–Re and Al on Si wafers. Thin W–Re films, without Al, were also deposited on Si3N4 windows. The samples were annealed at different temperatures and characterized using Rutherford backscattering spectroscopy, x-ray diffraction, and transmission, and scanning electron microscopy (TEM and SEM). The W–30% Re sample was crystalline with a β-W structure after deposition, while the W–61% Re and the W–72% Re samples were amorphous and crystallized into the α-Mn structure (χ phase) at a temperature of 700 and 600 °C, respectively. All Al/W–Re/Si structures were stable against Al penetration up to 500 °C. At an annealing temperature of 550 °C signs of a reaction leading to the formation of (W,Re)–Al12 could be observed. At 600 °C the barrier layers failed completely due to a reaction between W, Re, Al, and the Si substrate. SEM analyses of the bare Si substrate after the metal layer had been chemically removed showed that etch pits were formed after annealing the diffusion barrier structure at 550 °C for 30 min. The failure of the diffusion barriers is most likely due to local penetration of Al through defects in the films.

Spectrophotometric determination of rhenium with dithio-oxamide in strongly alkaline medium

The interaction between rhenium(VII) and dithio-oxamide in strongly alkaline medium in presence of tin(II) chloride as reluctant has been studied. A purple complex is obtained, with λ max 526 nm and ϵ max = 4.0 × 10 3 l.mole −1.cm −1. The reaction has been applied to the determination of rhenium in tungsten—rhenium alloy after its anodic electrochemical dissolution in alkaline medium. A 1000-fold excess of molybdenum or tungsten does not interfere. A modification of the proposed method can be used as a spot-test for rapid control of rhenium content in industrial solutions.

Mechanical properties and structure of tungsten-rhenium powder metallurgy deformed alloys

The properties of tungsten-rhenium alloys, obtained by compact sintering of dispersed powders which formed a tungsten-rhenium solid solution at relatively low temperatures, were investigated. Three systems were compared: a tungsten alloy with 2% rhenium, an alloy with dispersed additions of yttrium and hafnium oxides, and commercially pure tungsten. The properties included ductile-to-brittle transition temperature, bend strength, yield strength, and crack resistance. Structures were determined by scanning electron microscopy. Tungsten alloyed with small additions of rhenium possessed higher plasticity and in other mechanical properties was similar to cast and deformed alloys of the same composition.

Development of High-Reliable Tungsten-Rhenium Alloy Thermocouple for Measuring in-Core Helium-Gas Temperature in Very High Temperature Gas-Cooled Reactor

Composite-type stranded tungsten-rhenium alloy thermocouples have been developed for measuring in-core outlet-gas temperature of 950 °C to 1200 °C in VHTR. Long-term high-temperature out-pile and in-pile tests for these thermocouples and postirradiation examinations were made. The results showed their reliable and stable performances at temperatures of 1000 °C and 1400 °C.

Radiation-induced precipitation in fast-neutron irradiated tungsten-rhenium alloys: An atom-probe field-ion microscope study

The phenomenon of radiation-induced precipitation has been studied in W-10 at.% Re and W-25 at.% Re alloys, utilizing the atom-probe field-ion microscope technique. Specimens of these alloys were irradiated in the Experimental Breeder Reactor II to a fast-neutron fluence of ∼ 4 × 10 26neutrons m −2 (E > 0.1MeV) at 575, 625 and 675°C. This corresponds to 8.6 dpa and an average displacement rate, for the two year irradiation time, of 1.4 × 10 −7dpa s −1. Extrapolation of the solvus lines on the W-Re phase diagram indicates that the 10 at.% Re alloy is subsaturated with respect to the solvus line of the primary solid solution, while the 25 at.% Re alloy is supersaturated, with respect to the same solvus line. In the case of the 10 at % Re alloy coherent, semicoherent and possibly incoherent precipitates with the composition ∼ WRe and a disc-shaped morphology — one or two atomic planes thick — were detected at a number density of ∼10 22m −3, and a mean diameter of ∼ 5.7nm. For the 25 at.% Re alloy coherent, semicoherent and incoherent precipitates with the composition ∼ WRe 3 were detected; the precipitate's number density is ∼ 10 23m −3 with a mean diameter of 4.0 nm. None of the ∼ WRe or the ∼ WRe 3 coherent precipitates were associated with either line or planar defects or with any impurity atoms. Therefore, a true homogeneous radiation-induced precipitation occurs in these alloys. A physical argument is presented for the nucleation of WRe or WRe 3 precipitates in the vicinity of displacement cascades produced by primary knock-on atoms.

Substructure effect on low temperature plasticity of tungsten-rhenium alloys

Substructure effect on low temperature plasticity of tungsten-rhenium alloys

Spectrophotometric determination of rhenium in alkaline solution

The reaction of perrhenate with hydroxylammonium chloride (NH3OHCl) has been studied. Hydroxylammonium chloride reacts with rhenium in 8–10 M sodium hydroxide solution to produce a yellow complex which has λmax. at 300 nm with a molar absorptivity of 7.9 × 103 l mol–1 cm–1. The stoicheiometry of the complex has been studied spectrophotometrically using different procedures. A method for the spectrophotometric determination of rhenium has been developed, and this has been applied to the determination of rhenium in molybdenum-rhenium and tungsten-rhenium alloys.

Experimental problems in the use of solid oxide electrolytes

Several observations are described concerning the use of solid oxide electrolytes in kinetic and thermodynamic studies in liquid-metal-oxygen systems. These observations include: degradation of commercially available oxide electrolytes, degradation of electrodes and contamination from conventionally purified argon protective atmospheres. The conductivity of commercially available calciastabilized zirconia (CSZ) and yttria-stabilized zirconia (YSZ) decreased with use at elevated temperatures in contact with liquid metals. This decrease causes discrepancies in the values of oxygen diffusivity unless appropriate correction factors are used. Tungsten-wire-liquid-metal electrodes were observed to oxidize even when the average oxygen activity in the liquid metal was below the threshold level for tungsten oxidation; however, rhenium and tungsten-rhenium alloys performed satisfactorily. A low residual oxygen level in purified argon introduces large errors in oxygen solubility measurements. The rate of absorption of the residual oxygen in argon by liquid indium was studied and a rate constant established. A method for oxygen solubility measurements which avoids these sources of error is discussed.

Effect of palladium on the process of diffusional alloy formation and microstructure during the sintering of tungsten-rhenium powders with well-developed surfaces

Low-temperature coreduction of tungsten trioxide and ammonium perrhenate can be employed as a means of preparing active tungsten-rhenium powders having well-developed surfaces and good sinterability. The action of an alloy formation activator manifests itself most strongly with active powders produced by the method of low-temperature coreduction of tungsten trioxide and ammonium perrhenate. Diffusional reaction between the tungsten and rhenium in such a case begins already during the reduction process. At temperatures of intense alloy formation phase interlayers of activator solid solutions form at grain boundaries in tungsten-rhenium alloys. As a result, the diffusional permeability of the boundaries to rhenium atoms grows, which activates the process of diffusional alloy formation.

A simple method to produce ions of the heavy metals Nb, Mo, Ta, W and Re in a hollow cathode source

A method is reported, by which ions of the heavy metals Nb, Mo, Ta, W and Re which have low vapour pressures, can be produced. These materials are formed into helices and used as filaments in a hollow cathode ion source. From the thermally vaporised material ion currents of a few μA can be extracted. For rhenium a tungsten-rhenium alloy is used.

Calibration of tungsten–rhenium alloy thermocouples below room temperature

Three tungsten-rhenium alloy thermocouple combinations are calibrated and numerically represented by a polynomical in temperature for the range 77–290 K. (AIP).