Showing papers on "Carbide published in 1990"

Method of preparing silicon carbide surfaces for crystal growth

Abstract: The invention is a method of forming a substantially planar surface on a monocrystalline silicon carbide crystal by exposing the substantially planar surface to an etching plasma until any surface or subsurface damage caused by any mechanical preparation of the surface is substantially removed. The etch is limited, however, to a time period less than that over which the plasma etch will develop new defects in the surface or aggravate existing ones, and while using a plasma gas and electrode system that do not themselves aggravate or cause substantial defects in the surface.

Composite abrasive compact having high thermal stability

Abstract: An abrasive compact with a substantially solid body is provided from a mass of abrasive particles which are bonded together on a particle-to-particle basis. A network of interstices is formed within the body by removing the metallic second phase by-product of a solvent catalyst sintering aid. The network of interstices is filled with the carbide by product of a non-catalyst sintering aid forking a solid body. A substrate is bonded to some of the particles and to some of the carbide filling the network of interstices.

Stable and metastable phase equilibria in the chemical interaction between aluminium and silicon carbide

Abstract: An experimental investigation was carried out on the Al-C-Si ternary system under atmospheric pressure and at temperatures up to 1900 K. From the results obtained, a thermodynamic model based on stable and metastable phase equilibria in the Al-C-Si ternary system was set up in order to provide a general description of the chemical interaction between aluminium and SiC. According to this model, aluminium and SiC are in thermodynamic equilibrium at every temperature lower than 923 K. At 923±3 K, i.e. at 10 K below the melting point of pure aluminium, a quasiperitectic invariant transformation occurs in the Al-C-Si system. In this transformation, solid aluminium reacts with SiC to give Al4C3 and a ternary (Al-C-Si) liquid phase. The carbon content of this liquid phase is very low; its silicon content is 1.5±0.4 at%. From 923 to about 1620 K, aluminium partially reacts with an excess of SiC, leading to a metastable monovariant equilibrium involving SiC, Al4C3 and an aluminium-rich (Al-C-Si) ternary liquid phase, L. The carbon content of this liquid phase, L, remains very low whereas its silicon content increases with temperature from 1.5±0.4 at% at 923 K to 16.5±1 at% at 1620 K. In the temperature range 1670 to 1900 K, two other three-phased monovariant equilibria can be reached by reacting aluminium and SiC. These equilibria involve on the one hand SiC, Al4SiC4 and a liquid phase, L′, and on the other hand, Al4SiC4, Al4C3 and a liquid phase, L″. The former is a stable equilibrium, the latter is a metastable one. At temperatures higher than about 2200 K, the latter metastable equilibrium is replaced by two monovariant stable phase equilibria including the ternary carbide Al8SiC7.

Method of manufacturing semiconductor devices

Abstract: An improved method of manufacturing a semiconductor device wherein an insulating film, a conducting film, a first film to prevent conducting and refractory metal films from the reaction and a refractory metal film are sequentially deposited on a semiconductor substrate. Further, a second film is formed on the surface of the refractory metal film to prevent the exposed surface of the refractory metal film from the oxidization. Tungsten, molybdenum or the like is used as a refractory metal. A nitride film, a carbide film, or a silicide film of tungsten or molybdenum may be advantageously used as the second film.

Structural evolutions from polycarbosilane to SiC ceramic

Abstract: The pyrolysis process of a polycarbosilane into a microcrystalline silicon carbide ceramic has been followed up to 1700 ° C mainly by means of solid state29Si and13C nuclear magnetic resonance, transmission electron microscopy and X-ray diffraction analysis. A structural model has been proposed for the amorphous silicon carbide phase that is formed during the pyrolysis process. The ceramic obtained at high temperature is formed by a mixture of β-SiC and α-SiC; however, some difficulties in the identification of the crystalline phases have been pointed out.

Bond softening in monolayer graphite formed on transition-metal carbide surfaces

Abstract: Full phonon-dispersion curves of the graphitic layer on some transition-metal carbides were measured by using high-resolution electron-energy-loss spectroscopy. The graphitic layer on (111) surfaces of TaC, HfC, and TiC showed anomalous softening within the layer, whereas the graphite layer on TaC(001) is similar to bulk graphite. The measured phonon dispersion has been analyzed with a force-constant model, and it has been revealed that the force constants for vertical angle bending and for bond twisting are much weaker in the former case. This is ascribed to the charge transfer into the overlayer from the substrate, resulting in the weakening of the \ensuremath{\pi} bond in graphite. The clear contrast in variations of phonons between the graphitic layer on TaC(111) and that on TaC(001) indicates that the microscopic structure at the interface determines the charge transfer.

Meteoritic silicon carbide: pristine material from carbon stars

Abstract: All five gases in interstellar silicon carbide grains have grossly nonsolar isotopic and elemental abundances that vary with grain size but are strikingly similar to calculated values for the helium-burning shell of low-mass carbon stars. Apparently these grains formed in carbon-star envelopes, and were impregnated with noble gas ions from a stellar wind. Meteoritic SiC provides a detailed record of nuclear and chemical processes in carbon stars.

Liquid‐Phase Reaction‐Bonding of Silicon Carbide Using Alloyed Silicon‐Molybdenum Melts

Abstract: The authors have investigated reaction-forming of silicon carbide by the infiltration of carbonaceous preforms using alloyed silicon melts, in order to synthesize composite materials free of the residual silicon phase that has previously limited mechanical properties and upper use temperatures. In this approach, rejection of the alloying component(s) from the primary silicon carbide phase into the remaining melt results in the formation of a secondary refractory phase, such as a silicide, in place of residual free silicon. Experiments conducted in the Si-Mo melt system show that relatively dense ({gt}90%) silicon carbide-molybdenum silicide materials free of residual silicon and residual carbon can be obtained. A model for reactive infiltration based on time-dependent permeabilities is proposed. Processing variables important for control of the reaction rate relative to the infiltration rate, and associated processing flaws, are discussed.

Solidification processing and tribological behavior of particulate TiC-Ferrous Matrix composites

Abstract: Particulate TiC-reinforced ferrous matrix composites were processed by solidification of (1) an FeTiC melt of appropriate composition from which particulate titanium carbide precipitates and (2) an FeC melt in which particulate titanium carbide is dispersed through electromagnetic stirring. The microstructure of composites processed by precipitating titanium carbide was controlled by controlling melt composition and homogeneity, as well as cooling rate. That of composites processed by dispersing titanium carbide powder in a steel or cast iron melt was controlled by controlling the original melt composition, volume fraction and particle size of titanium carbide added, mixing temperature and time, and cooling rate. The specific wear rate and the friction coefficient between a diamond stylus and the polished surface of composite specimens decreased with increasing volume fraction of titanium carbide and decreasing carbide particle size and spacing. They also decreased with increasing steel matrix microhardness, achieved through heat treatment and martensitic transformation.

Metal/ceramic joining.

Abstract: This review article on metal/ceramic joining is subdivided into the description of research activities in the fields of active metal brazing and diffusion bonding published in the last decade. Informations are given on active metal brazing of oxide, nitride, and carbide ceramics and on diffusion bonding of alumina, zirconia, magnesia, silicon nitride, aluminum nitride and silicon carbide ceramics to metals. Ultra high vacuum diffusion bonding and experiments using the model combination Nb/alumina are also regarded. Emphasis is laid on a concise reproduction of experimental data concerning the bonding conditions and the determintion of bond strength. The review demonstrates that much effort was devoted to studies on the formatin of interfacial reaction layers and on the efficiency of interlayers additonally introduced between the ceramic and the metal part to reduce internal stresses caused by thermal expansion misfit of the materials to be bonded.

A thermally activated solid state reaction process for fabricating ohmic contacts to semiconducting diamond

Abstract: Techniques have been developed to produce ohmic contacts to naturally occurring boron doped semiconducting diamond. Thin films of Mo, Mo/Au, and Mo/Ni/Au deposited on diamond produced adherent ohmic contacts after annealing at 950 °C. A thermally activated solid state reaction which produces a refractory carbide precipitate at the original diamond/metal interface is the principal factor in affecting the properties of the contacts. The interface reaction has been characterized using Auger electron spectroscopy, scanning electron microscopy, x‐ray diffraction, metallography, and I‐V measurements.

Light emitting diode device and method for producing same

Abstract: A light emitting diode device comprises an n type silicon carbide substrate having first and second major surfaces opposite to each other at least inclined at a predetermined angle not less than 3° from a {0001} plane, an n type silicon carbide layer grown on the first major surface, a p type silicon carbide layer grown on the n type silicon carbide layer, a p type ohmic electrode formed on a partial area of the p type silicon carbide layer, and an n type ohmic electrode formed on a partial area of the second major surface. The diode element has a substantially trapezoidal form in a cross section orthogonal to the first major surface. The diode element has the side of the p type silicon carbide layer broader than the side of the second major surface and is supported at the side of the type silicon carbide layer fixed to a supporting stem.

Phase Equilibria in Fe-Mn-Al-C Alloys

Abstract: Phase constitutions of Fe-(20-30)wt%Mn-(0-10)wt%Al-C alloys have been investigated by electron probe microanalysis and transmission electron microscopy. The phase relations between austenite and perovskite carbide, (Fe, Mn)3AlC in the temperature range of 900-1 200°C have been carefully examined. An L12-type ordered structure, which was reported to be formed in rapidly solidified alloys as a metastable phase has not been detected in specimens aged at temperatures above 600°C.

Mechanically driven syntheses of carbides and silcides

Abstract: Most metal carbides or slicides may be synthesized at room temperature, by ball milling mixtures of elemental powders for some tens of hours with a vibratory mill. Both stable and metastable compounds containing a high density of defects can be obtained. In general, phases stable at low temperatures are synthesized. This observation allows us to confirm recent estimations for the maximum temperature (∼600 K) attained in these powders during mechanical alloying. Exceptions are found for some MSi2 suicides with M = titanium, iron or molybdenum for which both low- and high-temperature phases are formed.

Carbon fibrils, method for producing same, and encapsulated catalyst

Abstract: A process for preparing carbon fibrils using discrete, unfused, metal-containing catalytic particles encapsulated in non-graphitic carbon, a carbide, or an organic polymer.

Tribological Properties of PM212: A High-Temperature, Self-Lubricating, Powder Metallurgy Composite

Abstract: This paper describes a research program to develop and evaluate a new high temperature, self-lubricating powder metallurgy composite, PM212. PM212 has the same composition as the plasma-sprayed coating, PS212, which contains 70 wt percent metal-bonded chromium carbide, 15 wt percent silver and 15 wt percent barium fluoride/calcium fluoride eutectic. The carbide acts as a wear resistant matrix and the silver and fluorides act as low and high temperature lubricants, respectively. The material is prepared by sequential cold press, cold isostatic pressing and sintering techniques. In this study, hemispherically tipped wear pins of PM212 were prepared and slid against superalloy disks at temperatures from 25 to 850 C in air in a pin-on-disk tribometer. Friction coefficients range from 0.29 to 0.38 and the wear of both the composite pins and superalloy disks was moderate to low in the 10(exp -5) to 10(exp -6) cubic mm/N-m range. Preliminary tests indicate that the material has a compressive strength of at least 130 MPa over the entire temperature range of 25 to 900 C. This material has promise for use as seal inserts, bushings, small inside diameter parts and other applications where plasma-sprayed coatings are impractical or too costly.

Morphology and properties of low-carbon bainite

Abstract: Morphology of low-carbon bainite in commercial-grade high-tensile-strength steels in both isothermal transformation and continuous cooling transformation is lathlike ferrite elongated in the 〈11l〉b direction Based on carbide distribution, three types of bainites are classified: Type I, is carbide-free, Type II has fine carbide platelets lying between laths, and Type III has carbides parallel to a specific ferrite plane At the initial stage of transformation, upper bainitic ferrite forms a subunit elongated in the [−101]f which is nearly parallel to the [lll]b direction with the cross section a parallelogram shape Coalescence of the subunit yields the lathlike bainite with the [−101]f growth direction and the habit plane between (232)f and (lll)f Cementite particles precipitate on the sidewise growth tips of the Type II bainitic ferrite subunit This results in the cementite platelet aligning parallel to a specific ferrite plane in the laths after coalescence These morphologies of bainites are the same in various kinds of low-carbon high-strength steels The lowest brittle-ductile transition temperature and the highest strength were obtained either by Type III bainite or bainite/martensite duplex structure because of the crack path limited by fine unit microstructure It should also be noted that the tempered duplex structure has higher strength than the tempered martensite in the tempering temperature range between 200 °C and 500 °C In the case of controlled rolling, the accelerated cooling afterward produces a complex structure comprised of ferrite, cementite, and martensite as well as BI-type bainite Type I bainite in this structure is refined by controlled rolling and plays a very important role in improving the strength and toughness of low-carbon steels

Multilayer coated cemented carbide cutting insert.

Abstract: An indexable metalcutting insert is provided having a cobalt cemented tungsten carbide substrate (32) with a multilayer refractory coating (34) thereon. The substrate (32) has a cobalt content of 6.1 to 6.5 weight percent and is characterized by a hardness of 90.8 to 91.6 Rockwell A and a magnetic coercive force of 110 to 180 ÷rstads. The coating (34) contains at least a plurality of alumina layers (42) which are separated from and bonded to each other by a group IVB metal nitride (44), such as titanium nitride, and which are bonded to the substrate (32) by a backing layer of 5 to 8 ν in thickness, composed of a carbide and/or carbonitride of titanium zirconium and/or hafnium.

Behavior of grain boundary chemistry and precipitates upon thermal treatment of controlled purity alloy 690

Abstract: Grain boundary composition and carbide composition and structure were characterized for various microstructures of controlled purity alloy 690. Heat treatments produced varying degrees of grain boundary chromium depletion and precipitate distributions which were characterizedvia scanning transmission electron microscopy (STEM). Convergent beam electron diffraction revealed that the dominant carbide is M23C6, and energy dispersive X-ray analysis (EDAX) determined that the metallic content was about 90 at. pct chromium. A discontinuous precipitation reaction was observed and is attributed to a high degree of carbon supersaturation. Grain boundary composition measurements confirm that chromium depletion is controlled by volume diffusion of chromium to chromium-rich grain boundary carbides in the temperature range of 873 to 1073 K. Grain boundary chromium levels as low as 18.8 at. pct were obtained by thermal treatment at 873 K for 250 hours and 973 K for 1 hour. A thermodynamic and kinetic model developed for alloy 600 was modified to describe the development of the chromium depletion profile in alloy 690 during thermal treatment. Experimentally measured chromium profiles agree well with the model results for the dependence of the chromium depletion zone width and depth on various input parameters. The establishment of the model for alloy 690 allows the chromium depletion zone width and depth to be computed as a function of alloy composition, grain size, and temperature. The chromium depletion profiles and the precipitate structure and composition of controlled purity 690 are compared to those of controlled purity 600. A thermodynamic analysis of the carbide stability indicates that other factors, such as favorable orientation relationships, play an important role in controlling the precipitation of Cr23C6 in nickel-base alloys.

Artificial heart valves: improved blood compatibility by PECVD a-SiC:H coating.

Abstract: Implants are steadily increasing in importance as substitutions for body functions. With the present state of the art, the limitations of the application of cardiovascular implants are due to insufficient performance of biomaterials. Present research in this field is being concentrated on efforts to improve the thrombus resistance of conventional materials by coating with semiconducting materials to actively influence the electrochemical interaction between the condensed matter and blood proteins. Based on an electrochemical model of the interaction of fibrinogen with an artificial surface and the resulting requirements for improving hemocompatibility, a coating of amorphous hydrogenated silicon carbide deposited by plasma-enhanced chemical vapor deposition (PECVD) is presently under evaluation as a special coating material for cardiovascular prostheses and is herein described (1). In particular, first results are published concerning the optimum deposition parameters in the PECVD process and cell culture tests. Experimental results of comparative partial thromboplastin time studies serve the purpose of proving the validity of the electrochemical reaction model referring the hemocompatibility of implantable materials to their semiconducting surface properties. The aim of this article is to demonstrate a feasible method for an antithrombogenic surface modification based on doped amorphous silicon carbide films that is in full conformance to the above mentioned model.

Microstructure and stability of FeCrC hardfacing alloys

Abstract: The microstructure and high temperature stability of an iron-based hardfacing alloy of nominal composition Fe-30Cr-38C (weight per cent) deposited by manual metal arc welding has been investigated using microscopy, microanalysis, dilatometry and thermodynamic modelling In the as-deposited condition the undiluted alloy was confirmed to consist of a mixture of M 7 C 3 carbide and metastable austenite containing a high chromium concentration Since the properties of the alloy can depend on the stability of the austenite, annealing experiments were carried out to investigate the decomposition of the austenite into a mixture of ferrite and carbides The results demonstrate that at temperatures around 750 °C the austenite starts to decompose rapidly, beginning with the precipitation of M 23 C 6 carbides, although the final equilibrium phase mixture is simply chromium-depleted ferrite and M 7 C 3 The implications of these results are discussed with respect to the potential applications of the alloy

A mechanism for the formation of lower bainite

Abstract: A diffusional mechanism for the formation of lower bainite is proposed based primarily on transmission electron microscopy (TEM) observations of isothermally reacted specimens of Fe-C-2 pct Mn alloys. The mechanism involves the initial precipitation of a nearly carbide-free ferrite“spine,” followed by sympathetic nucleation of“secondary (ferrite) plates” which lie at an angle to the initial“spine.” Carbide precipitation subsequently occurs in austenite at ferrite: austenite boundaries located in small gaps between the“secondary plates.” An“annealing” process then occurs in which the gaps are filled in by further growth of ferrite and additional carbide precipitation; the annealing out of ferrite: ferrite boundaries between impinged“secondary plates” completes this process. This annealing stage contributes to the final appearance of lower bainite sheaves as monolithic plates containing embedded carbides. The present mechanism accounts for the single variant of carbides oriented at an angle to the sheaf axis repeatedly reported in lower bainite; it is also consistent with the previous observation of one“rough” side and one“smooth” side of lower bainite“plates.”

Reaction between SiC and W, Mo, and Ta at elevated temperatures

Abstract: The stability of W, Mo, and Ta in contact with single‐crystal β‐SiC at elevated temperatures has been investigated using Auger sputter profiling. All three metals were found to form a thin‐mixed layer of metal carbide and silicide upon metal deposition at room temperature. This layer is thought to be the result of surface defects which weaken the Si—C bonds and allow a low‐temperature reaction to occur. Upon heating, the Ta readily reacts with the SiC substrate and forms a mixed layer of Ta carbide and silicide at annealing temperatures as low as 400 °C, however, the W/SiC and Mo/SiC systems are stable and change very little after annealing at 850 and 800 °C, respectively.

Factors Affecting the Transverse Tensile Strength of Unidirectional Continuous Silicon Carbide Fibre Reinforced 6061 Aluminum

Abstract: A study of the micromechanics of continuous silicon carbide fibre rein forced 6061 aluminum has been carried out using generalised plane strain non-linear finite element analysis. An interface element has been developed enabling separate shear and tensile strengths to be assigned, with a quadratic interaction equation. Residual stresses due to manufacturing were included in the analysis.The effect on transverse tensile strength of fibre packing geometry, fibre spacing, resid ual stresses, interface strengths and matrix material properties were investigated. It was found that the interface strength is the most important factor. Residual stresses are beneficial, these being largely controlled by the yield strength of the matrix material at the time the residual stresses are set up. Fibre packing and spacing and matrix strength do not significantly affect predicted strength.

Thin film transistor

Abstract: PURPOSE:To obtain an excellent semiconductor by forming a polycrystalline Si film and a thin SiC film thereon, obtaining a low resistance layer of sourcedrain in only the SiC film, and constituting a buried channel structure and a wide gap drainsource structure CONSTITUTION:An active layer on a glass substrate 1 is constituted of polycrystalline Si carbide film 3 A gate insulating film 4 and a gate electrode 5 are formed in a gate electrode pattern By ion implantation using the gate electrode 5 as a mask, a shallow source-drain region is formed in the polycrystalline Si carbide film in the self alignment manner After a passivation film 6 is formed, a contact hole is formed, and a source-drain electrode 7 is formed Thereby field effect mobility is increased, OFF-current is decreased, leak current is reduced, and high breakdown strength is maintained

Natural occurrence of silicon carbide in a diamondiferous kimberlite from Fuxian

Abstract: CONSIDERABLE debate surrounds the existence of silicon carbide in nature, mostly owing to the problem of possible contamination by man-made SiC. Recently, Gurney1 reviewed reports of rare SiC inclusions in diamonds, and noted that SiC can only be regarded as a probable rather than proven cogenetic mineral. Here we report our observation of clusters of SiC coexisting with diamond in a kimberlite from Fuxian, China. Macrocrysts of α-SiC are overgrown epitaxially by β-SiC, and both polymorphs are structurally well ordered. We have also measured the carbon isotope compositions of SiC and diamonds from Fuxian. We find that SiC is more enriched in 12C than diamond by 20‰, relative to the PDB standard. Isotope fractionation might have occurred through an isotope exchange reaction in a common carbon reservoir. Silicon carbide may thus ultimately provide information on carbon cycling in the Earth's mantle.

Electron spectroscopic identification of carbon species formed during diamond growth

Abstract: Carbon deposits formed during filament assisted diamond film growth were characterized with x‐ray photoelectron spectroscopy (XPS) and electron energy‐loss spectroscopy (EELS). The samples were transferred between the growth chamber and the ultrahigh vacuum analytical chamber without exposure to air. These results are presented with an emphasis on data analysis for carbon chemical state identification. By comparison of the C(1s) binding energies to a highly oriented pyrolytic graphite standard, we are able to distinguish pure carbon species, such as diamond and graphite, from compounds, such as SiC and CxHy. For substrates with Z≤30, the loss electrons from the C(1s) core level are free from overlap with the substrate core levels; therefore, EELS spectra can be obtained by x‐ray excitation of the C(1s) level. These EELS data can then be used as a fingerprint for distinguishing between diamond, graphite, and carbides. For samples with mixed deposits of diamond and graphite, or carbide and diamond, curve fi...

Adhesion and tribological properties of diamond films on various substrates

Abstract: The adhesion of diamond films deposited by microwave plasma-enhanced CVD on various substrates can be quantitatively determined by an indentation method. The friction behaviors of diamond-coated cemented carbides sliding against a brass ring were studied. The wear resistance of the diamond-coated cemented carbide inserts and the commercial inserts with the other ceramic coatings were compared and directly evaluated by turning tests. Effects of the coating conditions, the substrate materials, and the surface pretreatments of the substrate on adhesion, friction, and wear properties are discussed.