Showing papers on "Carbide published in 1971"

Carbides: Properties, Production, and Applications

Abstract: I The Structure and Physicochemical Properties of Carbides.- Structures.- Thermodynamic and thermophysical properties.- Electrophysical and magnetic properties.- Physicomechanical properties.- Chemical properties.- II Methods of Producing Carbides.- III Carbides of Metals of Group I.- Carbides of the alkali metals.- Carbides of metals of the copper subgroup.- IV Carbides of Metals of Group II.- Carbides of beryllium, magnesium, and the alkaline-earth metals.- Carbides of the zinc subgroup.- V Carbides of the Transition Metals.- Carbides of scandium, yttrium, and the lanthanides.- Carbides of the actinides.- Carbides of metals of subgroup IVa.- Carbides of metals of subgroup Va.- Carbides of metals of subgroup VIa.- Carbides of metals of subgroup VIIa.- Carbides of metals of group VIII.- VI Carbides of Elements of the Boron Group.- VII Silicon Carbide.- VIII Chemical Properties of Carbides.- IX The Applications of Carbides.- References.

Second phase dissolution

Abstract: A detailed theoretical study was made of the dissolution of precipitates. The kinetic analyses of the atomic mechanisms included the concurrent effects of diffusion, interface reaction, and curvature, and considered the more complex problems of precipitate arrays and nondepleted matrices. The general formalism thus obtained was used to interpret the results of an experimental investigation of the technologically important problem of the dissolution of “reluctantly soluble” carbides in the Fe-C-V system. It was found that vanadium carbide (and iron carbide as well) were quite easily dissolved while complex alloy sulfides, silicates and oxides (possibly associated with the presence of vanadium) persisted, with little if any dissolution. Previous views of the reasons for poor hardenability were reevaluated in light of these results.

Intergranular Corrosion of Austenitic Stainless Steel

Abstract: The well‐known susceptibility of austenitic stainless steels to intergranular corrosion after heat‐treatment in the temperature range of 550°–800°C (i.e., "sensitization") has long been attributed to depletion of Cr from regions of the alloy matrix adjacent to grain boundaries in which had precipitated. Those regions of the steel in which the local Cr composition falls below about 12% have a diminished ability to form a passive film and hence corrode preferentially.We have made thermodynamic calculations of the equilibria in and near grain boundaries in order to determine the chromium content in the vicinity of carbide particles. The calculations show that the equilibrium chromium content is a strong function of the temperature and of the carbon and alloy content of the steel. It is inferred from the analysis that variations in the susceptibility to intergranular attack are determined primarily by changes in the equilibrium chromium content near the carbides and not by changes in the number and distribution of particles. For instance, above 800°C the chromium content near the carbides is high enough to produce passivity, and the alloy is immune not because of the absence of carbides but because chromium depletion is not severe. Experimental studies of rates of grain boundary attack as functions of temperature and composition have confirmed the predictions of the analysis.A further factor of less importance is the distribution of carbides in the grain boundary. Calculations were made to determine the Cr concentration gradient within the boundary between carbide particles as a function of temperature and composition as well as the Cr gradient normal to the boundary. These calculations predict a strong interdependence between susceptibility to intergranular corrosion, carbide particle spacing, and sensitizing temperature. Experimental results on thinned samples of sensitized material corroded in a Strauss solution and examined by electron microscopy are in good agreement with predicted effects.

Cubic boron nitride/sintered carbide abrasive bodies

Abstract: Abrasive bodies comprising combinations of cubic boron nitride crystals and sintered carbide are disclosed. These composite bodies are prepared by superpressure processes. Cubic boron nitride contents of up to about 99 volume percent have been successfully employed in certain constructions. Similar abrasive bodies have been prepared from mixtures of cubic boron nitride, diamond and carbide powder.

Precipitation of carbides at γ─α boundaries in alloy steels

Abstract: Austenite containing 1 to 2 wt% vanadium and 0.2 wt% carbon, held in the range 600 to 850 degrees C transforms to an extremely fine dispersion of V$\_{4}$C$\_{3}$ in ferrite. The carbide particles are nucleated on the $\gamma $-$\alpha $ phase boundary at successive positions during the transformation, forming sheets of precipitate which are 5 to 30 nm apart, while the individual particles are 3 to 10 nm diameter (interphase precipitation). High resolution electron microscopy has provided details of the morphology and crystallography of the carbide particles and the transformation front. A similar reaction has been studied in an iron +6.3wt% tungsten +0.23wt% carbon alloy in which M$_{6}$C precipitates on a much coarser scale enabling precise observations to be made on the transformation front. Interphase precipitation has also been examined in an iron +3.45 wt% molybdenum +0.22 wt% carbon alloy. A model is proposed for the interphase precipitation which takes into account the observed morphology and crystallography of the carbide phases and of the ferrite.

Abrasive bodies of finely-divided cubic boron nitride crystals

Abstract: ALUMINUM ALLOYS OF NICKEL, COBALT, MANGANESE, IRON, VANADIUM AND CHROMIUM HAVE BEEN FOUND TO PROVIDE SUCCESSFUL BONDING MECHANISMS FOR THE PREPARATION OF CUBIC BORON NITRIDE (CBN) COMPACTS. THESE BONDING MEDIA ARE PARTICULARLY EFFECTIVE FOR PREPARING COMPACTS OF CBN CRYSTALS SMALLER THAN ABOUT 30 MICROMETERS IN LARGEST DIMENSION. THE PREPARATION OF TOOL INSERTS MADE OF CUBICBORON NITRIDE CRYSTALS BONDED TO AND SUPPORTED ON A SINTERED CARBIDE MASS IS DESCRIBED WHEREIN SUCH AN ALUMINUM ALLOY IS USED AS THE BONDING MEDIUM.

Hardness anisotropy, deformation mechanisms and brittle-to-ductile transition in carbide

Abstract: The slip plane for TiC0.8′ VC0.84 and substoichiometric tantalum carbide has been determined as {110} using microhardness indentation at room temperature. Under the same conditions, HfC0.98 also slips on {110} but TaC0.96 slips on {111}. At low temperatures {110} slip is characteristic of the Group IV and substoichiometric Group V transition metal carbides while stoichiometric Group V carbides probably deform preferentially on {111} at all temperatures. This behaviour is explained in terms of two models for the crystal structures of the carbides. The Group IV carbides are described by a close-packed metal lattice whereas the structure of stoichiometric Group V carbides is more open. Various physical and mechanical properties and the effects of changing carbon content have been correlated on the basis of the models. In particular, an explanation of the brittle-to-ductile transition in carbides is proposed.

Chemical vapor deposition coatings on titanium

Abstract: A process for coating titanium-containing substrates with a dense, adherent, chemically vapor deposited coating by initially effecting a pro-tective, adhesion-promoting, intermediate layer on the titanium surface and subsequently depositing from the vapor phase a metal nitride, carbide, or carbonitride coating on the intermediate film. For example, a titanium article may be initially nitrided to provide a titanium nitride protective layer and titanium nitride, titanium carbide, or titanium carbonitride may subsequently be deposited from the vapor phase onto this film to provide a dense, adherent, protective coating on the titanium article. The barrier layer serves to pro-mote adhesion between the titanium substrate and the final overlay and to prevent reaction between the substrate and such a reaction ingredient as titanium tetrachloride, which is a preferred constituent for supplying titanium in the titanium carbide, nitride, or carbonitride final coating.

Electronic Structure of Cubic Refractory Carbides

Abstract: Recent electron (ESCA) and x‐ray emission and absorption spectra for the cubic refractory carbides of Group IVb (TiC, ZrC, HfC) and Group Vb (VC, NbC, TaC) are summarized. Based on an interpretation of the experimental data by using self‐consistent‐field calculations on free atoms and ions and supported by an approximately self‐consistent augmented‐plane‐wave calculation on TiC, a model of the electronic structure is presented. The metal atoms are positive and the carbon atoms negative in the refractory carbide. The electrostatic (Madelung) energy of a cubic carbide is less than one‐third of the total binding energy and equals the heat of formation of the carbide.

Carbide Contamination of Silicon Surfaces

Abstract: The techniques of grazing angle reflection high‐energy electron diffraction (RHEED), mass spectroscopy, and electron microscopy have been used to study carbide contamination of silicon samples heated in ultra‐high vacuum. The RHEED data showed that the surfaces of silicon crystals heated between 800°–1000°C were covered with β‐SiC crystallites well oriented with respect to the substrate. Heating between 1000°–1100°C formed a nonoriented β‐SiC phase, and further heating above 1100°C removed the surface carbide. CO and CO2 evolution was observed when samples were heated above 800°C. The carbide reappears with heating to 800°C if the carbide free surface is exposed to atmosphere or left in the vacuum environment for a sufficient time. Electron micrographs of platinum‐shadowed carbon replicas from samples contaminated with β‐SiC indicated that the carbide existed within protuberances at the surface. Data from samples heated to 950° and 1050°C showed particles ∼400 A in size, of cylindical shape and tapering towards the top; the surface density of the protuberances was observed to vary from 2×107 to 6×109/cm2. In all cases of carbide formation, the carbide results from the chemical reaction of a carbon‐containing adsorbate with the silicon surface. Although a gaseous origin for an adsorbate has been demonstrated, additional adsorption probably also results from chemical cleaning of the sample. Surface steps on the silicon are correlated with the presence of β‐SiC protuberances (or other artifacts) and appear to have been pinned by these particles.

Plastic flow and fracture of tantalum carbide and hafnium carbide at low temperatures

Abstract: Knoop and Vickers hardness measurements have been made on tantalum carbide and hafnium carbide single crystals. The hardness varies with orientation of the indenter in the crystal, but indentations in the two carbides are of very different character, TaC behaves in a relatively ductile manner and deforms plastically before cracking, while HfC exhibits extremely limited plastic flow and cracks on indentation. Moreover, the preferred slip plane is {111} in TaC but is {110} in HfC. These results are related to the reported physical properties of these carbides. In particular, the observed mechanical behaviour of TaC appears to be consistent with the more metallic nature of this carbide.

Mass of polycrystalline cubic system boron nitride and composites of polycrystalline cubic system boron nitride and other hard materials, and processes for manufacturing the same

Abstract: This invention gives bonded or compact bodies of polycrystalline cubic system boron nitride and substantially uniform composites of polycrystalline cubic system boron nitride and other hard materials, for example, metal borides, such as titanium boride and zirconium boride, covalent or metallic cabides, such as boron carbide, silicon carbide, titanium, carbide, tungsten carbide and chromium carbide, metal nitrides, such as titanium nitride, tantalum nitride, silicon nitride and aluminum nitride, metal oxides, such as alumina and silica, complex oxide such as garnet and agate, and diamond. Further, this invention provides a process of obtaining the bonded body of these materials which comprises subjecting hexagonal system boron nitride powder, or a mixture of hexagonal system boron nitride powder and cubic system boron nitride crystal powder or powders of the above-mentioned hard materials to high temperatures and high pressures.

The application of fracture mechanics to cemented tungsten carbides

Abstract: The difficulties encountered in the measurement of the toughness of cemented tungsten carbides are discussed and the benefits that might be expected from an application of fracture mechanics to the problem are described. A simple method for the measurement of the fracture-toughness parameter, KIC, for the more brittle grades of carbide is considered. The method involves indenting a beam-shaped specimen with a Knoop diamond to produce a crack, and loading the pre-cracked specimen to failure in four-point bending. Results from two grades of cemented carbide are presented and show that a standard error of the mean KIC of ∼3% can be obtained from a set of 10 measurements, with a minimum of specimen preparation and no special testing equipment. The results show also that the toughness of the cemented carbide can be affected by grain-size variations within the same batch of material and by the pressing direction during manufacture.

Elastic moduli of niobium carbide and tantalum carbide at high temperature

Abstract: The Young's, shear and bulk moduli of polycrystalline NbC 0.95 and TaC 0.99 were determined from room temperature to 1500°K by the sonic resonance technique. The Young's and shear moduli decrease linearly with increasing porosity, and also decrease with increasing temperature, in agreement with the Wachtman's empirical equation. The bulk modulus decreases with increasing porosity and with increasing temperature. The Gruneisen constant and Debye temperature of both carbides were determined. The Poisson ratio increases with increasing temperature.

Carbides in M-50 high speed steel

Abstract: The carbides in M-50 high speed tool steel were studied in detail. The dissolution of carbides as a function of austenitizing temperature, and their precipitation as a function of tempering temperature were characterized by X-ray diffraction and microchemical analysis. The carbides in the annealed steel are M23C6, M6C, M2C, and MC. Upon austenitizing, with increasing temperatures, the carbides dissolve in the order: M23C6, metastable M2C, M6C, and MC. The residual carbides in the heat treated steel are MC and stable M2C. The solvus temperatures of M23C6 and M6C were determined. Upon tempering the hardened steel, with increasing tempering temperatures, carbides precipitate in the order: M23C6, metastable M2C, MC, and M6C. It is shown that the composition of the precipitated metastable M2C is different from that of the residual stable M2C and it varies with the tempering temperature.

Superconductivity of molybdenum and tungsten carbides

Abstract: The superconducting critical temperatures of a total of 18 samples of α-Mo2C, β-Mo2C, η-MoC1−x and α-W2C have been determined resistively. The critical temperatures lie within the ranges 6°–7.3°, 5.1°–7.2°, 7.4°–8.9° and 2.95°–3.05°K, respectively. The critical temperature for β-Mo2C is much higher than found previously, and similar to that for α-Mo2C.

New Carbide, (Fe,Ni)23C6, found in Iron Meteorites

Abstract: THE common carbide in iron meteorites is the orthorhombic cohenite, Fe3C, known to metallurgists as cementite. A new cubic iron carbide has now been identified by X-ray powder photography of lumps, gouged under the microscope from small areas in polished sections of the Toluca meteorite. Fig. 1 shows a similar area in a specimen of the Canon Diablo meteorite. The cubic carbide occurs in the plessite fields of several such coarse octahedrites. The data from the powder photographs, excluding the lines from kamacite and taenite present in the sample, are given in Table 1. These lines can be indexed on a face-centred, cubic cell, with a = 10.55 A. The structural type can be deduced by observing the close similarity of this pattern to those given by the carbides Mn23C6 and Cr23C6, which have a complex cubic unit cell containing four formula units1. The data for the latter, with cell edge 10.66 A, taken from the American Society for Testing Materials (ASTM) file (14–407), are also shown for comparison in Table 1.

Discontinuous precipitation of M23C6 in austenitic steels

Abstract: Grain boundary precipitation of M23C6 has been studied in a 20% Cr-35% Ni stainless steel with two grain sizes during creep deformation at 700°C as well as during an ordinary ageing treatment at 700°C. A special etching technique was applied which showed how the grain boundary precipitation gave rise to depletion of alloying elements in a zone of uniform thickness, independent of the carbide distribution, and with a gradual decrease of the depletion towards the grain interior. At some places the carbide precipitation and grain boundary migration co-operated and in these cases there was a sharp change in alloying content across the grain boundary. This process was more frequent in creep tested samples and the degree of co-operation was larger in the coarse-grained material where even a few cases of lamellar, eutectic-like precipitation was observed. Such a grain size dependence is expected theoretically and is caused by the large difference in diffusivity between carbon and the other alloying elements. It is proposed that the various degrees of co-operation between carbide precipitation and grain boundary migration are all examples of discontinuous precipitation. The various proposed mechanisms for grain boundary migration during discontinuous precipitation are discussed on the basis of the present results.

Sintered hard metal product

Abstract: AN IMPROVED SINTERED HARD METAL COMPOSITION IS PROVIDED COMPRISED ESSENTIALLY OF REFRACTORY METAL COMPOUND GRAINS OR PARTICLES COATED WITH A REFRACTORY CARBIDE LAYER TO IMPART WETTABILITY TO REFRACTORY METAL COMPOUND GRAINS WHICH ARE DIFFICULT TO WET WITH SUCH BINDER METALS AS THE IRON GROUP METALS. THE WETTABLE REFRACTORY CARBIDE COATING IS FORMED BY DEPOSITING A LAYER OF THE CORRESPONDING REFRACTORY METAL UPON THE GRAINS FROM A HALIDE OF THE METAL, WHICH LAYER IS THEREAFTER CARBURIZED; OR THE CARBIDE COATING MAY BE PRODUCED SIMULTANEOUSLY ON THE SURFACE OF THE GRAINS FROM AN ATMOSPHERE COMPRISING HALIDE VAPOR IN THE PRESENCE OF A CARBURIZING AGENT, IN WHICH HYDROGEN MAY OR MAY NOT BE PRESENT. THE COATED REFRACTORY METAL COMPOUND GRAINS MAY OPTIONALLY BE MIXED WITH WETTABLE REFRACTORY METAL CARBIDE GRAINS IS PRODUCING SINTERED HARD METAL COMPOSITIONS.

Carbon, carbides, and methane in an apollo 12 sample.

Abstract: Total carbon in the Apollo 12 sample 12023 fines was 110 micrograms per gram of sample with a carbon isotopic abundance delta(13)C (relative to the Pee Dee belemnite standard) of +12 per mil. Hydrolysis of the fines with deuterium chloride yielded undeuterated methane along with deuterated hydrocarbons, thus confirming the presence of 7 to 21 micrograms of carbon per gram of sample as carbide and about 2 micrograms of carbon per gram of sample as indigenous methane. After vacuum pyrolysis of the fines to 1100 degrees C the following gases were detected in the relative abundance: carbon monoxide carbon dioxide methane. Variations of the delta(13)C value with the pyrolysis temperature indicated the presence of carbon with more than one range of isotopic values. The observed delta(13)C value of +14 per mil for lunar carbide is much higher than that of carbide in meteorites. These results suggest that lunar carbide is either indigenous to the moon or a meteoritic contribution that has been highly fractionated isotopically.