Showing papers on "Carbide published in 1973"

Platinum-Like Behavior of Tungsten Carbide in Surface Catalysis

Abstract: Tungsten carbide catalyzes the formation of water from hydrogen and oxygen at room temperature, the reduction of tungsten trioxide by hydrogen in the presence of water, and the isomerization of 2,2-dimethylpropane to 2-methylbutane. This catalytic behavior, which is typical of platinum, is not exhibited at all by tungsten. The surface electronic properties of the latter are therefore modified by carbon in such a way that they resemble those of platinum.

Strength and toughness of Fe-10ni alloys containing C, Cr, Mo, and Co

Abstract: The effects of C (0.10 to 0.20 pct), Cr (0 to 3 pct), Mo (0 to 2 pct), and Co (0 to 8 pct) on the yield strength, toughness (Charpy shelf energy), and tempering behavior of martensitic lONiCr-Mo-Co steels have been investigated. Variations in the carbon content between 0.10 and 0.20 pct result in yield strengths between 160 and 210 ksi (1.1 and 1.45 GN/m2) when these steels are tempered at 900° to 1000°F (480° to 540°C) for times of 1 to 100 h. These steels exhibit a secondary-hardening peak at 900° to 1000° F (480° to 540°C) where coarse Fe3C carbides are gradually replaced by a fine, dislocation-nucleated dispersion of (Mo, Cr)2C carbides. Maximum toughness at a given yield strength in these steels is only obtained when they are tempered for sufficiently long times so that the coarse Fe3C carbides are completely dissolved. Molybdenum is primarily responsible for the secondary-hardening peak observed in these steels. However, chromium additions do result in lower secondaryhardening temperatures and promote coarsening of the secondary-hardening carbide. Best combinations of strength and toughness are obtained with steels containing 2 pct Cr and 1 pct Mo. Cobalt increases the yield strength of these steels over the entire tempering range and results in a higher secondary-hardening peak. This effect of cobalt is attributed to 1) a retardation in the rate of recovery of the dislocation substructure of the martensite, 2) the formation of a finer dispersion of secondary-hardening carbides, and 3) solid-solution strengthening. The finer dispersion of secondary-hardening carbides in steels containing cobalt is favored by the finer dislocation substructure in these steels since the (Mo, Cr)2C carbide is dislocation-nucleated. This fine dispersion of (Mo, Cr)2C carbide combined with the high nickel content accounts for the excellent combination of strength and toughness exhibited by these steels.

Thermodynamics of carbon in nickel, iron-nickel and iron-chromium-nickel alloys

Abstract: Iron-nickel alloys with 8 and 16 wt pct nickel and iron-chromium-nickel alloys with 8 pct nickel and chromium contents in the range of 2 to 22 pct were equilibrated with iron and nickel in flowing CH4-H2 gas mixtures and in sealed capsules under partial vacuum at temperatures between 700 and 1060°C. Carbon activities in these alloys were established from the carbon concentrations in the nickel by applying Henry’s law to the solubility of carbon in nickel that was determined in the temperature range of 500 to 1000°C. First-order free-energy interaction parameters were used to relate the carbon activities to composition and temperature in the single-phase austenitic Fe-Ni and Fe-Cr-Ni alloys. An expression was also developed to evaluate carbon activities in Fe-Cr-Ni alloys in the region of higher chromium contents (〉4 wt pct) that result in a two-phase austenite plus carbide mixture at these temperatures.

The wetting of carbon and carbides by copper alloys

Abstract: In a previous paper (J. Mater. Sci.5 (1970) 149) a model was developed to predict the wetting behaviour between carbon and copper alloys containing 1 at. % of a carbide forming element. In the present paper it is shown that the model can be applied successfully to alloys containing as little as 0.15 at. % chromium or vanadium and as much as 13 at. % titanium. A further development of the model is its use to predict carbide surface energies, the values derived being in good agreement with literature data.

Strengthening of Ferrite by Vanadium Carbide Precipitation

Abstract: When iron–vanadium–carbon alloys are transformed from the γ to the α state, a banded dispersion of vanadium carbide is formed as the transformation fronts move through the crystals. The strengthening resulting from this reaction in a series of alloys isothermally transformed in the range 725–850° C is shown to be dependent on the transformation temperature, since this determines the state of the dispersion. The mechanical properties are also sensitive to the volume fraction of carbide precipitate, which has been studied by changing the vanadium and carbon contents of the alloys. The dispersion can be further influenced by addition of alloying elements, e.g. manganese, which alters the kinetics of the reaction.

Procedures and Precautions in Machining Titanium Alloys

Abstract: Titanium alloys have unique machining properties. While the cutting forces are only slightly higher than in machining steels, there are other characteristics that make these alloys more difficult to machine than steels of equivalent hardnesses. For example, the chip-tool contact area in turning a titanium alloy is only about one-third to one-half as great as that for turning a steel. Also, the thermal conductivity of titanium alloys is about one-sixth of that of steels. This combination of a small contact area and the low thermal conductivity results in very high cutting temperatures. At a cutting speed of 100 ft. /min., the temperature developed at the cutting edge of a carbide tool is 1000oF when cutting a steel, while on the titanium alloy, the temperature reaches 1300oF. Hence, the cutting speeds on titanium alloys must be lower in order to maintain a tool-chip temperature below that which results in short tool life.

Performance of (U,Zr)C-graphite (composite) and of (U,Zr)C (carbide) fuel elements in the Nuclear Furnace 1 test reactor

Abstract: The properties of and reactor test results for two types of nuclear- propulsion-reactor fuel elements containing uraniumzirconium carbide, (U,Zr)C, are reported. Composite fuel elements containing graphite and ~35 vol% carbide, along with fuel elements consisting only of carbide, were tested in Los Alamos Scientific Laboratory's Nuclear Furnace 1 reactor for l09 min at peak power densities of ~4500 MW/m/sup 3/ and temperature up to 2500 deg K. Fission-fragment damage to the graphite phase of the composite fuel elements increased the roomtemperature thermal resistivity of the matrix ninefold, resulting in unexpected high mass losses of carbon. The carbide elements developed both longitudinal and transverse fractures but did not fragment into small-size particles. (auth)

Constitution of ternary titanium-tungsten-carbon alloys☆

Abstract: The ternary alloy system Ti-W-C was investigated by means of melting point, differential-thermoanalytical, X-ray diffraction, and metallographic techniques on hot-pressed and heat-treated, as well as melted, alloy specimens and a phase diagram from 1500 °C through the melting range established. Above 2530 °C, titanium monocarbide and the isomorphous cubic high temperature phase in the W-C binary system are completely miscible and the solid solution has a congruent (maximum-type) melting point of 3130 °C at the approximate composition (Ti0.54W0.44)C0.75. Below 2530 °C, the tungsten exchange in the cubic monocarbide is temperature-dependent and decreases to about 50 at.% at 1400 °C. The titanium exchange in W2C is less than 3 at.% at 1500 °C and reaches a maximum of 8 at.% at 2680 °C. In addition to the ternary congruent melting point, four reaction isotherms occur in the system: Two are pseudobinary eutectics, monocarbide + graphite at 3030 °C, and monocarbide + tungsten-rich metal alloy at 2700 °C; peritectic melting of the binary WC results in a class II reaction L + C⇄cubic monocarbide + WC(hex) at 2760 °C, and a fourth isotherm at 2680 °C is associated with a ternary eutectic between metal, monocarbide (B1), and W2C. Pseudobinary eutectic melting between the monocarbide and the metal phase is directly attributable to the large stability difference between titanium and tungsten carbide, and the measured tie line distribution in the two-phase range metal + monocarbide is in accordance with estimates from known thermodynamic values for the binary boundary phases. The phase behavior in pseudobinary monocarbide solutions is largely determined by the relative lattice size of the boundary carbides, except for systems (M, W)C1 − x (M = Ti, Zr, Hf, V). which show extra stabilization due to bonding effects.

Method for coating a substrate to provide a titanium or zirconium nitride or carbide deposit having a hardness gradient which increases outwardly from the substrate

Abstract: A method for coating a substrate with titanium nitride or titanium carbide or zirconium nitride or zirconium carbide is described wherein physical vapor deposition in a vacuum is used, and wherein the substrate is biased by an electrical potential and the composition of the deposit is changed by introducing a gas during the deposition to produce a hardness gradient in the deposit which increases outwardly from the substrate.

Composite wire drawing die

Abstract: Composite wire drawing die construction is described in which a centrally-located mass of diamond, cubic boron nitride or a polycrystalline mixture thereof defines at least the throat of the wire drawing hole, the mass being flanked or girded by at least one mass of metal bonded carbide that is directly bonded thereto. The composite is readily ground into the form of a solid of revolution. In the preferred construction (for dies for drawing 0.008 inches diameter wire and larger) a composite assembly includes at least one high strength metal ring that is press fitted around a composite body or sub-assembly comprising a polycrystalline mass of diamond girded by a metal-bonded carbide jacket.

Hard metal body

Abstract: A sintered hard metal body is provided with a thin wear-resistant surface coating consisting of an outer layer of ceramic oxide and an intermediate layer of carbide or/and nitride.

Nucleation limitation and hardenability

Abstract: The relation between nucleation theory and hardenability of steels has been critically examined. The effect on hardenability of most elements with the exception of boron and strong carbide forming α-stabilizers, is found to be semiquantitatively consistent with classical nucleation theory. The “anomalous” effects of boron, chromium and molybdenum, are discussed in terms of possible physical interference of precursor reactions with ferrite formation.

Carbon-coated articles and method of making same

Abstract: A pyrolytic carbon-coated article having improved wear resistance as a result of providing a thin wear-resistant layer just below the outer surface. The layer contains an alloy of pyrolytic carbon and a metal or metalloid carbide and is made by changing the composition in a deposition region without halting deposition so as to create transition regions adjacent the layer which include gradually lesser amounts of the alloying carbide.

Vacancy ordering in vanadium carbides based on V6C5

Abstract: The ordered arrangement of carbon vacancies in vanadium carbides near V6C5 has been analysed by means of selected-area electron diffraction and high-voltage electron microscopy. A new type of ordered distribution of carbon vacancies is found at non-stoichiometric compositions between V6C5 and V8C7. This structure can be expressed as a longperiod structure consisting of the enantiomorphic domains based on the structure V6C5 which was determined by Billingham. Bell and Lewis (1972). The periodic domain boundaries with spacing eleven times the nearest-neighbour interatomic distance are directly observed by electron microscopy.

High-temperature oxidation characteristics of the carbides of the Group VI transition metals

Abstract: 1. A study was made of the oxidation of the carbides of the Group VI transition metals during 5 hours' exposure to air at temperatures ranging from 500 to 1200°C. 2. Thermodynamic studies, metallographic examinations, and x-ray phase analyses demonstrated that the oxidation of Cr3C2, Mo2C, and WC involves the formation of oxides of the relevant metals and of free carbon, which subsequently oxidizes to CO and CO2. 3. It is shown that the oxidation resistance of the carbides of the Group VI metals is governed by the character and properties of the main oxides of the relevant metals and also by the appearance of carbon, which takes part in the formation of gaseous reaction products.

Electronic Structure of Vanadium Carbide

Abstract: The electronic structure of stoichiometric vanadium carbide has been computed using the augmented-plane-wave (APW) method and the energy bands for nonstoichiometric phases have been determined with the APW---virtual-crystal approximation. The energy bands exhibit a very strong dependence on the relative sizes of the assumed APW-sphere radii for vanadium and carbon. Bands for the nonstoichiometric phases show a marked deviation from a rigid-band behavior as the composition is varied. The results of x-ray-emission, heat-capacity, magnetic-susceptibility, and Hall-effect measurements are discussed in terms of the computed bands.

Method for metal coating diamonds so as to improve the interfacial bond strength

Abstract: A method of producing metal coated diamond particles in which the coatings are strongly bonded to the diamond particles characterised in that a layer of an alloy consisting of a major proportion of a metal such as copper, nickel or iron and a minor proportion of a carbide-forming metal such as titanium, chromium or vanadium is applied to the uncoated particles and then the coated particles are heat treated to a temperature of between 500*C and a temperature just below the melting point of the alloy for a time sufficient to enable a bonding carbide layer to form at the alloy/diamond interface, the steps being carried out in a non-oxidising atmosphere. The invention further provides diamond particles having bonded thereto an alloy comprising a major proportion of nickel and a minor proportion of a carbide-forming metal such as titanium, chromium or vanadium, the bonding being achieved by means of a carbide layer, which is preferably continuous, at the alloy/diamond interface.

Elimination of carbide segregation to prior particle boundaries

Abstract: Carbide segregation to the prior boundaries of particles used in powder metallurgy to generate an article is eliminated through the use of a nickel-base alloy powder which coordinates carbon with the amount of Mo and W which can form detrimental amounts of undesirable carbides and with Cb, Ta, Hf and Zr which are strong formers of a desirable MC-type carbide.

Effect of Aging on the Anodic Behavior of Ni-Cr-Mo Alloys

Abstract: The precipitation response of corrosion resistant alloys based on the Ni-Cr-Mo phase diagram is complex with both intermetallic and carbide phases being formed during aging in the 650 to 1...

Method of forming a hard facing on the body of a tool

Abstract: A hard facing wear pad usable, for example, by brazing to a digger tooth or the like. The wear pad is from 70 to 85% by volume particles of cemented metal carbide in a metal matrix having a melting point not substantially higher than the melting point of the metal cementing the carbide. The cemented carbide particles are in the size range of from about 6 to 30 U.S. Sieve, and the thickness of the pad is within limits determined by the cemented carbide particle size.

Wear Characteristics of Burs

Abstract: A wear test was conducted to evaluate carbide dental burs. There is great variability within each bur type, which renders a particular bur highly unpredictable; this can be correlated to the variability in the carbide material. There is little hope that existing burs will be improved through changes in the sintered carbide system alone.

Method of fabricating nickel base superalloys having improved stress rupture properties

Abstract: Improved superalloy powder materials consisting of a powder mixture of a substantially carbon free nickel base superalloy containing gamma prime phase and a metastable carbide such as vanadium carbide (VC), titanium carbide (TiC) or chromium carbide (Cr3C2) in an amount sufficient to provide a controlled carbon content in the resulting mixture. The mixture is then consolidated into a shape by heat and pressure, after which it may be mechanically worked at a temperature below the recrystallization temperature to thereby promote grain growth in the shape, followed by heat treating the shape at a temperature above the recrystallization temperature to solution the metastable carbide and permit grain growth. Finally, the shape is subjected to an aging treatment at a temperature below the recrystallization temperature to reprecipitate the gamma prime and carbide phases in the matrix and the new grain boundary areas.

Composite eutectic alloy and article

Abstract: A unidirectionally solidified anisotropic metallic composite body of improved stability and high temperature properties is provided with a solid solution matrix of a superalloy of the nickel-base or cobalt-base type and comprising, by weight, at least about 2% Re and less than about 0.8% Ti. Embedded in the matrix is an aligned carbide reinforcing fibrous phase, preferably one selected from carbides of Ta, V or their alloys and mixtures.

The partitioning of refactory metal elements in hafnium-modified cast nickel- base superalloys

Abstract: Data from the electron microprobe have been used to elucidate the role of hafnium in altering the microstructure of the nickel-base superalloys B-1900, Alloy 713 LC, Udimet 700, and Mar-M246. The addition of about 1.3 to 2.0 pct Hf to these alloys improves their strength and ductility at both room temperature and 760°C. The data indicate that hafnium partitions to the surface of the MC carbides, replacing titanium and some molybdenum and/or tungsten in the carbide. On the basis of the observed morphology and composition of the carbides, it is postulated that, primarily, hafnium modifies the solidification sequence, which a) results in the formation of discrete, uniformly distributed MC carbides, b) retards the formation of secondary carbides, and c) contributes indirectly to solid solution strengthening of the matrix.