Showing papers on "Carbide published in 1995"

Synthesis and characterization of carbide nanorods

Abstract: THE properties and potential applications of carbon nanotubes filled with other materials have aroused much speculation1–5. Strategies for filling nanotubes include in situ growth in an arc reactor using metal/carbon composites2,5 and the capillarity-driven filling of open nanotubes using liquid reagents3,4. Here we report an alternative approach to the synthesis of nanoscale structures based on nanotubes, in which the tubes are converted to carbide rods by reaction with volatile oxide and/or halide species. In this way we have been able to prepare solid carbide nanoscale rods of TiC, NbC, Fe3C, SiC and BCx in high yield with typical diameters of between 2 and 30 nm and lengths of up to 20 urn. Preliminary studies show that these rods share the properties of the bulk materials (such as magnetism and superconductivity), suggesting that they might allow the investigation of the effects of confinement and reduced dimensionality on such solid-state properties. These carbide nanorods might also find technological applications in nanostructured composite materials.

A covalent micro/nano-composite resistant to high-temperature oxidation

Abstract: ADVANCED ceramic materials that can withstand high temperatures (over 1,500 °C) without degradation or oxidation are needed for applications such as structural parts for motor engines, gas turbines, catalytic heat exchangers and combustion systems1,2. Hard, oxidation-resistant ceramic composites and coatings are also in demand for use on aircraft and spacecraft. Silicon nitride (Si3N4) and silicon nitride/carbide (Si3N4 /SiC) composites are good candidates for such high-temperature applications2,3. Commercial Si3N4 parts can be used in oxidizing environments up to 1,200–1,300 °C (ref. 4), but are oxidized at still higher temperatures. Here we describe the synthesis of a covalent ceramic composite which is resistant to oxidation at temperatures up to 1,600 °C. The composite is formed from an amorphous silicon carbonitride, which crystallizes at high temperature into a composite of α-Si3N4 microcrystals and α-SiC nanocrystals. The oxidation resistance stems from the formation of a passivating surface layer of SiO2 a few micrometres thick.

Composite cermet articles and method of making

Abstract: Methods for making, methods for using and articles comprising cermets, preferably cemented carbides and more preferably tungsten carbide, having at least two regions exhibiting at least one property that differs are discussed. Preferably, the cermets further exhibit uniform or controlled wear to impart a self-sharpening character to an article. The multiple-region cermets are particularly useful in wear applications. The cermets are manufactured by juxtaposing and densifying at least two powder blends having different properties (e.g., differential carbide grain size or differential carbide chemistry or differential binder content or differential binder chemistry or any combination of the preceding). Preferably, a first region of the cermet comprises a first ceramic component having a relatively coarse grain size and a prescribed binder content and a second region, juxtaposing or adjoining the first region, comprises a second ceramic component, preferably carbide(s), having a grain size less than the grain size of the first region, a second binder content greater than the binder content of the first region or both. These articles have an extended useful life relative to the useful life of monolithic cermets in such applications as, for example, wear. The multiple region cermets of the present invention may be used with articles comprising tools for materials manipulation or removal including, for example, mining, construction, agricultural, and metal removal applications.

Properties of ultra-fine grain binderless cemented carbide ‘RCCFN’

Abstract: Conventional binderless cemented carbide is known as WC-3% TiC-2% TaC cemented carbide with a mean WC grain diameter of about 2 μm, which does not include a binder phase. This alloy, however, has no binder phase and therefore low strength. The authors investigated the effects of mean diameter of raw WC powder on mechanical characteristics, and found that the smaller the mean diameter of raw WC powder, the lower the temperature at which sintering is possible and the higher the hardness and strength becomes. An investigation was also made on the effects of grain growth suppression additives on the alloy using 0.6 μm diameter WC powder, which offers the highest mechanical characteristics, with the objective of enhancing characteristics through finer grains. Hardness increased with additional amounts of Cr 3 C 2 and VC. Strength peaked at a certain additive amount, with superior values of H R A = 95.5 and transverse-rupture strength = 1.8 GPa. The microstructure was found to be composed of only very fine and uniform carbides; a mirror surface of 7 nm Rtm was obtained by mirror polishing. These characteristics make it possible for this alloy to be used in various optical applications.

Hardfacing composition for earth-boring bits

Abstract: A hardfacing composition comprises at least 60% by weight of hard metal granules including a quantity of sintered carbide pellets and a quantity of cast carbide pellets. The cast and sintered carbides are selected from the group of carbides consisting of chromium, molybdenum, niobium, tantalum, titanium, tungsten, and vanadium carbides and alloys and mixtures thereof. The balance of the hardfacing composition is matrix metal with traces of flux or deoxidizer, and alloying elements. All percentages given are pre-application ratios.

Application of fine grained tungsten carbide based cemented carbides

Abstract: Fine grained submicron cemented carbides with a market share of 10–15% of total carbide consumption are characterized by an almost optimal combination of hardness and toughness. They are mainly used in machining wood and wood based materials, plastics, composites, ferrous and non-ferrous metals as well as in chipless operations such as in can tooling, high pressure punches and for wear parts. Tailored submicron cemented carbide has widened the application range of carbide and has led to a multifold improvement in abrasive wear life.

Physicochemical Mechanism of the Interaction between Cobalt Metal and Carbide Particles To Generate Toxic Activated Oxygen Species

Abstract: Hard metal alloys (or cemented carbides) are made of a mixture of tungsten carbide particles (WC, more than 80%) cemented in cobalt metal powder (Co, 5-10%). The inhalation of hard metal particles may cause an interstitial pulmonary disease, the mechanism of which involves an interaction between Co and WC particles. Some epidemiological data also suggest that hard metal dust can induce lung cancer in workers. In a macrophage culture model, butylated hydroxytoluene (1 mM) protected from the cytotoxicity of hard metal particles, suggesting a possible involvement of lipid peroxidation in the toxicity of these powders. In a biochemical system, a mixture of Co and WC particles, but not Co or WC alone, stimulated the production of thiobarbituric acid-reactive substances from arachidonic acid. Using a spin trapping system applied to aqueous particulate suspensions and electrochemical techniques, we present experimental evidence that the association of Co and carbide particles represents a specific toxic entity producing large amounts of activated oxygen species. The mechanism of this interaction proceeds through the oxidation of cobalt metal catalyzed at the surface of carbide particles and resulting in the reduction of dissolved oxygen. This physicochemical property of hard metal particles provides a new basis for interpreting their inflammatory action and their possible carcinogenic effect on the lung.

Steel tooth bit with a bi-metallic gage hardfacing

Abstract: An earth boring bit rotatable cutter having a first hardfacing composition of carbide particles selected from the class of cast and macrocrystalline tungsten carbide dispersed in a steel matrix deposited on the gage surface of at least some of the heel row teeth. A substantial portion of these particles are characterized by a high level of abrasion resistance and a lower level of fracture resistance. A second hardfacing composition of carbide particles selected from the class of spherical sintered and spherical cast tungsten is dispersed in a steel matrix deposited over at least the crest and an upper portion of the gage surface to cover the corner that tends to round during drilling. A substantial portion of the particles of this composition are characterized by a high level of fracture resistance and a lower level of abrasion resistance.

Electrodeposition of nickel/silicon carbide composite coatings on a rotating disc electrode

Abstract: Composite coatings suitable for protection against wear were prepared by electrodeposition from a nickel Watts solution containing silicon carbide particles maintained in suspension. To obtain a better understanding of hydrodynamic effects on the codeposition process a rotating disc electrode, immersed in a vertical rising flow, was used. The local concentration of embedded SiC along the radius of the disc electrode was studied as a function of suspension concentration, rotation rate and the particle mean diameter. The effect of a rheoactive polymer was also examined. Although it is generally admitted that the particle incorporation rate is governed by a two-step adsorption process, the experimental results show that it is also dependent on the spatial distribution of the wall fluid flow. The normal component of the fluid velocity promotes particle impingement, whereas the parallel component tends to eject the loosely fixed particles. The competition between the forces which tend to maintain particles attached to the surface and the shear force which tends to remove them, depends on several parameters, in particular the surface chemistry and the size of the particles, the flow rate and the current density.

Carbon nitride films synthesized by combined ion-beam and laser-ablation processing.

Abstract: Carbon nitride thin films on Si(100), with N concentrations ranging from 37% to 45% have been synthesized by pulsed laser ablation of graphite under a low-energy nitrogen-ion-beam bombardment. High-energy non-Rutherford backscattering has been employed to measure the atomic ratio of N to C in the films obtained. Electron-diffraction measurements, which give some new diffraction rings in addition to some found in previous work, and x-ray photoelectron-spectroscopy analyses, which give N 1s peaks at 399.1 and 397.4 eV, and C 1s peaks at 283.7, 284.5, and 286.9 eV, suggest the existence of covalent carbon-nitrogen bonds and polycrystallite structures in the amorphous carbide matrix of the films. Raman spectra have also been used to characterize the films. Qualitative tests indicate that the films are relatively hard and adhesive, with quite smooth surfaces.

Layered film made of ultrafine particles and a hard composite material for tools possessing the film

Abstract: Ultrafine particle-layered film for coating cutting tools. The film has more than two layers of at least two compounds consisting mainly of carbide, nitride, carbonitride or oxide of at least one element selected from a group consisting of IVa group elements, Va group elements, VIa group elements, Al, Si and B, and that each layer is made of ultrafine particles. Ultrafine particle-layered film improves hardness, strength, wear-resistance and heat-resistance of the tools.

Solubility products for titanium-, vanadium-, and niobium-carbide in ferrite

Abstract: Carbide- and nitride-forming elements, such as titanium, vanadium, and niobium, play important roles in the metallurgy of many modern steel products. These elements readily precipitate as stable carbides/nitrides during processing, even when present at relatively small levels. The precipitation of these alloy carbides/nitrides provides a means for controlling strength or hardness, grain size, the level of solute carbon, and other factors that affect properties and performance. Precipitation in austenite during hot deformation has received considerable attention and ''solubility products'' for many compounds have been published and used as alloy/processing development tools. The technologically important alloy nitrides generally exhibit relatively low austenite solubility. Alloy nitride solubilities in ferrite are even lower and, for practical purposes, can often be considered zero. In contrast, some alloy carbides exhibit substantial solubility in ferrite. However, thermochemical or solubility data on carbide/ferrite equilibria are sparse and, as a result, few experimental ferrite solubility relationships are available. A method is described herein for obtaining such a relationship from a known or assumed austenite solubility product using information on the activity coefficients of the solutes of interest. Solubility relationships for titanium-, vanadium-, and niobium-carbide in ferrite are then derived from published austenite solubility products and available thermodynamic informationmore » on binary Fe-Ti, Fe-V, and Fe-Nb solid-solutions.« less

Electrical properties of high-temperature oxides, borides, carbides, and nitrides

Abstract: High-temperature materials including oxides, borides, carbides, and nitrides encompass all types of conductors: metallic, semiconducting, and ionic. Their electrical conductivities are generally very sensitive to impurities regardless of the type of conductor. For large band-gap materials, which includes most of the oxides, the conductivities at low temperatures are frequently dominated by impurities or dopants, and intrinsic conduction only becomes significant above a temperature which depends largely on the level of dopant, the band gap and the defect structure of the base material. The borides, carbides, and nitrides of transition metals are metallic conductors with conductivities and temperature coefficients of resistivity comparable to that of their parent metals.

Formation of Nanostructural Materials Induced by Mechanical Processings ( Overview )

Abstract: Mechanical alloying (MA) was firstly developed to synthesize metallic matrix composite by mechanically incorporating preformed oxide and or carbide particles into a metallic matrix. A consecutive compaction process is applied to obtain bulk materials. During MA, powders are repeatedly welded, fractured and rewelded in a high energy mill leading to an intimate mixing on a nano/micro-scale with the possible formation of far from equilibrium phases. The versatility of MA is well known ; high volume, low energy mills can be used to commercially produced dispersion strengthened Al, Ni and other transition metal alloys. Various intermetallics and inorganic compounds (amorphous and/or nanocrystalline) have been synthesized by using higher energy mills which have been specially developed in some cases. Mechanical alloying, it appears, as suggested by T. H. Courtney et al., is the Alladin's lamp of powder processing. All the published works have shown that the reaction and end products of the MA process strongly depend on the milling conditions. As a consequence, it is obvious that an improved understanding of the dynamics of MA process is required to gain a full appreciation of the industrial potential of the technique for synthesizing materials. Recently, M. Abdellaoui and E. Gaffet have shown that the crystal to amorphous phase transition (at least in the case of the model Ni 10 Zr 7 ) only depends on the injected mechanically power, allowing a direct comparison among experiments performed using distinct type of milling apparatus (planetary milling machine, horizontal apparatus). An alternative method has been recently proposed by N. Malhouroux-Gaffet and E. Gaffet, for the solid state synthesis of disilicide powders exhibiting a wide contamination during the direct MA preparation : the mechanically activated annealing process (M2AP). Such a M2AP method has been applied to the synthesis of FeSi 2 , MoSi 2 , WSi 2 compounds. Such a method appears as being a well suitable one for the low temperature synthesis of refractory nanomaterials. Recent applications have been successfully performed to mechanically activated sintering (MAS).

Methods for making WC-containing bodies

Abstract: A method of forming a low level carbon high-density tungsten carbide-containing material includes sintering a preform which contains tungsten carbide powder and has a composition such that the resulting sintered material has at most 6.05 weight percent tungsten-bound carbon based on the total weight of tungsten and tungsten-bound carbon. This low level of carbon may be achieved by, prior to the sintering step, oxidizing the tungsten carbide powder sufficiently to achieve the desired substoichiometric carbon level in the sintered product or by adding a carbon-lowering material selected from the group consisting of tungsten, ditungsten carbide, and tungsten oxide. Optionally, other materials can be present in the preform such as carbon-getter metals and compounds thereof. The carbon-getter metals are those metals of which the carbides thereof are more thermodynamically stable than monotungsten carbide.

Observation of inverted-molecular compression in boron carbide.

Abstract: High-pressure neutron diffraction studies of boron carbide, ${\mathrm{B}}_{4}$C, to 11 GPa show that the icosahedral structural units are 23(4)% more compressible than the structure between them. This inverted-molecular compression is in accordance with qualitative predictions based on models of the bonding, but had not previously been observed directly. The results show the effect of the structural compression on the electrical resistivity to be more complex than present, semiquantitative models suggest.

Application of palladium- and rhodium-plating of the graphite furnace in electrothermal atomic absorption spectrometry

Abstract: Palladium- and Rh-plating of the graphite furnace has been evaluated as a method of introducing the metallic form of Pd and Rh for chemical modification in electrothermal atomic absorption spectrometry. It is shown that by electroplating Pd and Rh onto the inner surface of the tube, the pre-treated graphite surface may resemble the behaviour of the corresponding modifier. The resulting metallic layer is very effective in inhibiting the loss of volatile elements (e.g., As and Se), as well as reducing the influence of oxide and carbide formation (e.g., Si). The advantage of the proposed procedure of introduction of a solid chemical modifier is that the pre-treated tubes exhibit an extended analytical lifetime for the determination of As and Se, up to 80 and 160 firings in the presence of Pd and Rh, respectively. In the case of Si the Rh-plated graphite tube could last for about 100 firings.

Superhard composite materials including compounds of carbon and nitrogen deposited on metal and metal nitride, carbide and carbonitride

Abstract: A composite material having high hardness comprises a carbon nitrogen compound, such as CN x where x is greater than 0.1 and up to 1.33, deposited on a metal or metal compound selected to promote deposition of substantially crystalline CN x . The carbon nitrogen compound is deposited on a crystal plane of the metal or metal compound sufficiently lattice-matched with a crystal plane of the carbon nitrogen compound that the carbon nitrogen compound is substantially crystalline. A plurality of layers of the compounds can be formed in alternating sequence to provide a multi-layered, superlattice coating having a coating hardness in the range of 45-55 GPa, which corresponds to the hardness of a BN coating and approaches that of a diamond coating.

Microprocesses of metal dusting on iron

Abstract: In strongly carburizing atmospheres iron and steels are subject to 'metal dusting', a catastrophic carburization, leading to disintegration into a dust of carbon and metal particles. TEM investigations of iron foils in different states of this corrosion process have clearly shown now that unstable cementite is an intermediate in the reaction. The carbide is formed at the iron surface after supersaturation (ac > 1), its disintegration is started by graphite deposition on its surface (a c = 1). The carbon atoms from Fe 3 C disintegration are attached to the graphite planes which are vertically oriented to the cementite surface, the iron atoms diffuse through the graphite and agglomerate to small particles (∼20 nm) which act as catalysts for further carbon deposition from the atmosphere, till they are densely covered with graphite. The TEM investigations are in good agreement with preceding studies concerning kinetics and mechanisms of metal dusting.

Plate-crystalline tungsten carbide-containing hard alloy, composition for forming plate-crystalline tungsten carbide and process for preparing said hard alloy

Abstract: Disclosed are a plate-crystalline tungsten carbide-containing hard alloy which comprises 4 to 40% by volume of a binder phase containing at least one of iron group metals selected from Co, Ni and Fe as a main component; and the balance of a hard phase comprising tungsten carbide alone, or tungsten carbide and 50% by volume or less of a compound with a cubic structure selected from at least one of carbide and nitride of the 4a (Ti, Zr and Hf), 5a (V, Nb and Ta) or 6a (Cr, Mo and W) group element of the periodic table and mutual solid solutions thereof, and inevitable impurities, wherein when peak intensities at a (001) face and a (101) face in X-ray diffraction using Kα rays with Cu being a target are represented by h(001) and h(101), respectively, the tungsten carbide satisfies h(001)/h(101)≧0.50, a composition for forming a plate-crystalline tungsten carbide, and a process for preparing the plate-crystalline tungsten carbide-containing hard alloy.