Showing papers on "Carbide published in 1974"

Electronic Structure and Catalytic Behavior of Tungsten Carbide

Abstract: Tungsten carbide has been shown to be an effective catalyst for a number of reactions that are readily catalyzed by platinum, but not at all by tungsten, and it was speculated that this behavior is due to changes in the electron distribution when carbon is added to tungsten. A test of this hypothesis, made by measuring the valence band x-ray photoelectron spectrum of tungsten carbide and comparing it with the spectra of tungsten and platinum, shows that, near the Fermi level, the electronic density of states of tungsten carbide more nearly resembles that of platinum than that of tungsten.

Surface Electronic Properties of Tungsten, Tungsten Carbide, and Platinum

Abstract: The local electronic structures of the surface regions of tungsten, tungsten carbide, and platinum have been compared. Contrary to the hypothesis that the platinum-like catalytic activity of tungsten carbide results from the contribution of carbon valence electrons to the 5d band of tungsten, the width of the unfilled portion of the d band increases on going from tungsten to tungsten carbide.

Thermodynamics of the carbides in the system Fe-Cr-C

Abstract: Phase relations in the Fe-Cr-C system in the temperature range 900 to 1150°C have been studied using metallographic and X-ray methods and the electron microprobe. An isothermal section of the phase diagram at 1000°C is shown. Lattice dimensions of the three carbides were determined for several values of the ratio Cr:(Fe +Cr). The solubilities of the carbides at each temperature were determined by metallographic study of quenched specimens. The distribution of Cr between austenite (γ) and the several carbides was determined by use of the electron microprobe. Data of Wada et al on the activity of carbon were used to calculate activities at the y-phase boundary and the free energy of the several carbides as a function of their chromium content. The data are treated thermodynamically on the basis of assumed random mixing of Cr and Fe atoms in each carbide. While this randomness was not definitely proved, the assumption was shown to be reasonable and the results useful. Extrapolation to 0 and 100 pct Cr gives values for the standard free energy of Cr7C3 and the hypothetical carbides Cr36C, and Fe7C3.

Dense polycrystalline silicon carbide

Abstract: A dense silicon carbide material having improved electrically conducting properties is disclosed which is prepared by forming a homogeneous dispersion of silicon carbide, a sufficient amount of boron nitride, and optionally a boron containing additive and hot pressing the dispersion at a sufficient temperature and pressure whereby a dense substantially nonporous ceramic is formed. The silicon carbide material can be machined by electrical discharge machining or by electrochemical machining.

Carbide refining heat treatments for 52100 bearing steel

Abstract: The life of through-hardened 52100 anti-friction bearing components is improved if the excess carbides, undissolved during austenitization, are small and uniformly dispersed. One kind of carbide-refining heat treatment consists of 1) dissolving all carbides, 2) isothermally transforming the austenite to pearlite or bainite, and 3) austenitizing, quenching and tempering in the usual manner. Each step in this sequence of treatments was investigated, and the behavior of pearlitic and bainitic microstructures during subsequent austenitization was contrasted with the behavior of ferrite/spheroidized-carbide microstructures. It was shown that: 1) The usual hardening treatments given spheroidize-annealed bearing components result in an inhomogeneous microstructure, possibly due to the faster dissolution of carbides near austenite grain boundaries. 2) Austenitization of pearlite or bainite produces very uniform dispersions of ultra-fine carbides on the order of 0.1 µm diameter or less. 3) Specimens with ultra-fine carbides tend to have more retained austenite. 4) The rate of coarsening of ultra-fine carbides at austenitizing temperatures of 840°C and below, is slow enough so that conventional furnace heat treatments are satisfactory for producing this microstructure.

Coated steel product and process of producing the same

Abstract: A coated steel product, namely, a cutting instrument such as a band saw blade, in which the body of the blade is of steel, the tooth tip is of impulse hardened steel and the tip is covered with a coating of titanium carbide or refractory metal carbide, the coating metal or compound having been deposited by ion plating onto the surface of the tip. The process through which the cutting tool is produced includes preshaping and sharpening the tool, then ion cleaning the tips, bombarding the tips with ions of the titanium or refractory metal followed by reacting the titanium or refractory metal with a carbon containing chemical or their carbides and then simultaneously subjecting both the coating and the steel tip to a magnetic flux for impulse hardening primarily the steel tip. Other coatings of metal carbides, nitrides, borides and metal compounds are described.

The Isothermal Decomposition of Austenite in Simple Chromium Steels

Abstract: Two high-purity steels containing 12 and 5% chromium with 0.2% carbon have been isothermally transformed in the temperature range 775-600°C. The various ferrite and carbide morphologies encountered...

Electron Microscopy and Diffraction Study of the Carbide Precipitated at the First Stage of Tempering of Martensitic Medium Carbon Steel

Abstract: Crystal structure and precipitation mode of the carbide in a martensitic 0.45 wt%C steel tempered at 120 and 200°C have been studied by means of electron microscopy and selected area diffraction. In both plate-like and lath martensites, the precipitated carbide is η-Fe2C like the previous case of high carbon steel(Acta Met.,20(1972),645). The crystal morphology and the orientation relationships between the carbide and the matrix are also the same. In general, the precipitation occurs along dislocations, but it has been found that grain boundary precipitation also takes place in the non-parallel lath region and that in fine grains in this region the carbide precipitation does not occur. Some discussions are given to the crystal structure and the precipitation mode of the carbide. (Received September 4,1973)

Metal material for sliding surfaces

Abstract: In a metal material having a surface adapted to slide on a surface having a nickel-silicon carbide composite electroplated layer and subjected to a treatment for causing silicon carbide particles to project outward beyond the surface, the surface of the metal material is provided with porous hard chrome plating, whereby a lubricant may be deposited and retained in the porous plated layer.

Sintering behaviour of ultrafine NbC and TaC powders

Abstract: Compositional and microstructural changes upon firing ultrafine (300 to 400 A) stoichiometric NbC and TaC powder lots have been studied up to a temperature of 1600° C. Substantial amounts of oxygen impurities, mostly oxide particles or layers are eliminated by reductions with hydrogen, free carbon or the carbides themselves. TGA showed these reactions to take place at 700 to 1400° C with maxima around 1000 to 1100° C. Low temperature sintering is inhibited by this impurity and its removal is thus essential. Other impurities (Ni, Cr, Fe) were also found in the starting powders in total concentration 0.5 to 1%. They give rise to a liquid phase located at grain edges at temperatures as low as 1100° C which then controls microstructure development. It dissolves to some extent in the carbide matrix at high temperature, and has a tendency to rise to the free surface of the samples. Compositional and structural heterogeneities are thus produced between bulk and surface at high temperatures. Owing to these impurity effects, it was not possible to clearly evaluate the influence of powder granulometry.

Partial pressure of TiCl4 in CVD of TiN

Abstract: In developing a TiN coating for cobalt cemented WC–TiC–TaC tools, the effect of TiCl4 partial pressure in an H2+N2 atm was studied over the range of approximately 0.03–0.30 atm. The two temperatures of deposition studied were 1000 and 1080 °C. Low TiCl4 partial pressure combine to produce columnar grains > 10 μ in length and faster coating rates. Higher TiCl4 partial pressures in the range of 0.05–0.10 atm produce random oriented grains of approximately 1 μ or less and slower coating rates. TiCl4 pressures greater than 0.30 atm at 1000 °C nearly stop deposition of TiN. The TiN coating is especially useful in minimizing wear on carbide cutting tools.

Solid solubilities of oxygen, carbon and nitrogen in yttrium

Abstract: The solid solubilities of oxygen, carbon and nitrogen in yttrium metal have been investigated and a partial diagram is proposed for the Y-YN system. The temperature dependence of the solubility of each solute in α yttrium was fitted empirically to Arrhenius-type equations, and the heats of solution for the co-existing oxide, carbide or nitride phase were found to be 6.8 ± 0.4, 8.0 ± 1.0 and 11.6 ± 1.3 kcal/mole, respectively.

Diamond brazing method for slow wave energy propagating structures

Abstract: Diamond heat sink members are now employed to conduct thermal energy from slow wave structures in traveling wave type interaction devices to permit operation at high power levels. The diamond members are bonded to adjacent desired components by a method including heating an intermediate metal alloy of an inactive conductive metal and a small amount of a carbide constituent in a vacuum and the application of pressure. A critical temperature slightly above the melting point of the alloy of between 1000° C and 1100° C is required to wet and bond the alloy material to the diamond and any desired surface.

Investigation of silicon carbide single crystals doped with scandium

Abstract: Doping processes of silicon carbide crystals with scandium are investigated. It is shown that the scandium solubility in SiC is limited within the 1800 to 2600°C temperature range and amounts to (2 to 3) × 1017 cm−3. On doping silicon carbide crystals with scandium the VLS growth mechanism is possible. The luminescence spectra of the crystals are studied. It is found that nitrogen actively affects the luminescence intensity of silicon carbide doped with scandium. The depth of the radiative recombination centre in SiC (Sc) which is acceptor like is found to be 0.24 eV. [Russian Text Ignored].

Behavior of Austenitic Stainless Steels in Evaluation Tests for the Detection of Susceptibility to Intergranular Corrosion

Abstract: The characteristics, advantages, and limitations of various methods for the detection of susceptibility to intergranular corrosion in austenitic stainless steels due to carbide precipitation are discussed. Information on corrosion rates and acceptance limits in nitric acid and ferric sulfate-sulfuric acid tests is presented and illustrated by statistical data from the evauation of approximately 10,000 samples representing commercial AISI 300 series stainless steels.

Effect of titanium on the ductility of 26% chromium, lovv interstitial ferritic stainless steel

Abstract: The effect of titanium additions on the ductility of a 26%Cr steel containing about 0·005%C and 0·025%N was investigated. The microstructural changes which occurred during slow cooling werefollowed by means of chemical analysis, optical microscopy, X-ray diffraction and microprobe analyses performed on specimens water quenched from various temperatures within the range 2400°–600° F (1316°–316°C). The results were correlated with changes in room-temperature tensile properties and it was found that the low ductility of coarse-grained 26%Cr territic stainless steel was caused by the formation of a grain-boundary carbide or carbonitride phase at a temperature of about 1650°F(900°C). A titanium addition of 5(C+N) improved the ductility by preventing grain-boundary precipitation. TiN formed in the molten steel and, upon solidification, the random distribution of TiN particles served as nuclei for precipitation of chromium carbides within the grains. Increasing the titanium addition to 9·4(C+N) resulted ...

Process for preparing layers of silicon carbide on a silicon substrate

Abstract: In a process for producing an epitaxial layer of hexagonal silicon carbide on a silicon monocrystal substrate by simultaneous reduction or thermal decomposition of a gas mixture containing silicon halides and organosilanes, or mixtures thereof, hydrocarbons, and H 2 on said substrate, the improvement consisting of having water or a water-forming compound present in the gas mixture, which leads to especially pure silicon carbide, useful, e.g. as material for light emitting diodes.

The Effects of Mo and W on Solidification of High Speed Steels

Abstract: The effects of systematic variations in Mo content, W content, and the Mo:W ratio upon the freezing process and as-cast carbide morphology of high speed steels were studied for four series of alloys encompassing the nominal composition ranges of AISI type M2 (6 W-5 Mo-4Cr-2V-0.85C) and MIO (0W-8Mo-4Cr-2 V-0.85C) high speed steels. Thermal analysis, metallographic examination, and quantitative metallography were used to characterize these effects. The Hquidus, peritectic, and eutectic reactions were similarly influenced by molybdenum and tungsten, the peritectic temperature being strongly depressed by additions of either element. The types of carbides found in the as-cast structures did not vary, but the amount of feathery eutectic carbide (a layered structure of MC and M6C) was directly relatedto the total Mo plus W content. The amount of isolated vanadium-rich MC type carbide was seen to increase as the amount of feathery eutectic decreased, and also varied with the Mo:W ratio.

Coated laminated carbide cutting tool

Abstract: A coated, laminated crater-resisting, composite, cemented carbide cutting tool insert. The cutting insert has a cemented metal carbide core comprising about 85 to 98 percent by weight metal carbide, the majority being tungsten carbide cemented together with an iron-group element binder, such as iron, nickel or cobalt. The core supports a crater resistant layer of cemented carbide containing tungsten carbide and at least one carbide of a metal contained in Groups IVb or Vb of the periodic table, and the rake face and flanks of the cutting insert are coated with a hard surface coating, e.g. titanium carbide the hard surface coating being about 0.0001 to 0.001 inch thick.

Method for making a film of refractory material having bi-directional reinforcing properties

Abstract: A thin film of substantially defect-free pyrolytic graphite, useful as a bi-directional reinforcing material, is formed by vapor deposition on an inert liquid substrate surface and separated therefrom. The substrate temperature is substantially below the melting point of the refractory material and the substrate surface is smooth and free of stress to enable formation of a substantially defect-free film. The films of other refractory materials can be made similarly by first forming a pyrolytic graphite film on the substrate, and then vapor depositing a film of refractory material on the pyrolytic graphite surface. The pyrolytic graphite and refractory material films are then separated from the substrate surface and then separated from each other. Various refractory film materials can be made including pyrolytic graphite; boron; silicon; and refractory carbides, borides and nitrides. For making pyrolytic graphite films, it is preferable to use tin as the substrate, at a temperature of about 1,600*-1,800*C., at atmospheric pressure, a source gas consisting of methane and argon, helium, or hydrogen, and a film residence time on the substrate surface of about 0.16-2 minutes.

Cemented carbide material

Abstract: Cemented carbide material consists essentially of 70 to 90% by weight of tungsten carbide or of a mixture of tungsten and carbide at least one transition metal carbide, the transition metal being one other than tungsten selected from Groups IV to VI of the Periodic Table and 10 to 30% by weight of a binder. The binder contains 20 to 90% by weight of nickel, 10 to 80% by weight of cobalt and 5 to 25% by weight of chromium as the base ingredients thereof. The cemented carbide material has improved resistance to oxidation, to wear and especially to thermal cracking and is therefore suitable for rolls, guide rollers and dies for plastic hot working.

Effect of prior austenitic grain boundary composition on temper brittleness in a Ni-Cr-Sb steel

Abstract: Grain boundary segregation during temper embrittlement of an Sb-containing, Ni-Cr steel has been examined both by Auger electron analysis and by chemical analysis by neutron activation of residues of surface layers dissolved by etching intercrystalline fracture surfaces. No grain boundary segregation of either alloying additions or impurities was detected during austenitization or tempering. Redistribution of Cr, Ni, and Sb between carbide and ferrite was observed during tempering, but no grain boundary segregation was noted. Both Ni and Sb were observed to segregate to the boundaries during embrittling. The segregated Sb was shown to be uniformly distributed along the prior austenitic grain boundaries and to control the ductile brittle transition temperature of the alloy studied. Ni segregating to the prior austenitic boundaries during embrittling was shown to be localized in a phase other than the ferritic portions of the boundaries. A possible location was shown to be the ferritecarbide interfaces in the grain boundaries. Weakening of these normally tenacious carbide and ferrite interfaces could account for the change in mode of brittle failure from transcrystalline cleavage to intercrystalline along the prior austenitic grain boundaries that is observed in temper brittle steels.