Showing papers on "Carbide published in 1983"

Wear-Resistant Cobalt-Base Alloys

Abstract: Cobalt-base alloys have enjoyed extensive use in wear-related engineering applications for well over 50 years because of their inherent high-strength, corrosion resistance, and ability to retain hardness at elevated temperatures. Microstructurally, wear-resistant cobalt-base alloys consist of hard particles (Cr7C3) dispersed in cobalt-rich (Co > 50%) solid solution matrix alloys (generally Co-Cr-W/Mo). Recent investigations in the Cabot Corporation Technology Laboratories have shown that the adhesive and cavitation-erosion wear characteristics of these alloys are determined by the composition of the matrix alloy and are influenced to a large extent by a strain-induce fee → hep allotropie transformation in the matrix alloy. Further, it has been shown that the cobalt content in the matrix alloy can be decreased to approximately 30% without significantly degrading relevant wear or corrosion properties. Toughness and abrasive wear resistance, on the other hand, are determined primarily by carbide volume fraction and morphology. Large, hypereutectic carbides are generally preferred for good abrasive wear resistance but are detrimental to toughness considerations. The tribological measurements and microstructural correlations associated with these Cabot investigations are summarized and discussed in this paper.

Method for providing a coating layer of silicon carbide on the surface of a substrate

Abstract: The invention provides a novel method for providing the surface of various kinds of substrate articles, e.g. sapphire, quartz, alumina, metals, glass, plastics and the like with a coating layer of an amorphous silicon carbide of the formula Si x C 1-x , in which x is a positive number of 0.2 to 0.9, by exposing the surface of the substrate article to an atmosphere of plasma generated in a gaseous atmosphere of an organosilicon compound having no halogen or oxygen atom directly bonded to the silicon atom, such as hexamethyl disilane, optionally admixed with a vapor or gas of a hydrocarbon compound, e.g. methane, benzene and the like.

Stoichiometric limits of carbon-rich boron carbide phases

Abstract: The stoichiometric boron-to-carbon ratios of various carbon-rich boron carbide phases were investigated. Many powders or sintered pellets were analysed and the total boron, total carbon, free-boron and free-carbon concentrations were measured for each specimen before calculating the stoichiometric ratio. The methods described were applied to a large number of analyses and the standard deviation of the results was evaluated. The stoichiometric boron-to-carbon ratio for carbon-rich boron carbide phases was found to depend on the synthesis conditions. Boron dissolves up to 21.6 at.% C at low temperatures and up to 24.3 at.% C near the melting point. Free carbon is deposited as the result of a solid state phase transformation. The stoichiometry of boron carbide prepared by the magnesothermal reaction is B 3.63 C (approximately B 11 C 3 ). Boron carbide produced by arc melting boron oxide and carbon is a solid solution. This single carbide melts congruently at a temperature of approximately 2450°C with a carbon content of 18.4 at.% (B 4.45 C).

Hydrogen trapping in AISI 4340 steel

Abstract: Hydrogen trapping in AISI 4340 steel was investigated by thermal analysis at a constant heating rate of 3·4 K min−1. Peaks were observed in the evolution rate v. temperature plots at 388, 545, 611, 678, and 768 K in AISI 4340 steel samples having either pearlitic or spheroidized carbide structure, and analysis suggested that the evolution rate peaks at 388, 545, 611, and 768 K corresponded to the hydrogen release from ferrite/carbide interfaces, dislocations, microvoids, and MnS interfaces respectively. The activation energies for the evolution of trapped hydrogen from microvoids and MnS interfaces were found to be 48·3 and 72·3 KJ mol−1, respectively. It is observed that microvoids were formed at MnS interfaces during the thermomechanical process and these were related to the hydrogen embrittlement phenomena in AISI 4340 steel. It is also found that, in cold worked AISI 4340 steel having a pearlitic structure, the main trapping site of hydrogen was dislocations, not microvoids, the interface area...

Precipitation reactions during the heat treatment of ferritic steels

Abstract: The precipitation reactions in two ferritic steels, 9Cr-1Mo-V-Nb and 12Cr-1Mo-V-W, were studied. Analytical electron microscopy, optical microscopy, electrolytic extractions, and hardness measurements were used to determine the types, amounts, and effects of precipitates formed as a function of the heat treatment. The effect of variations in the austenitizing treatment was ascertained. In addition to variations in the austenitizing time and temperature, different cooling rates after austenitization were also used. Air cooling after austenitization (normalization) resulted in little precipitation in both alloys. Precipitation in the 12Cr-1Mo-V-W alloy after furnace cooling was found in all cases examined. Under certain conditions precipitation was also found after furnace cooling the 9Cr-1Mo-V-Nb alloy. However, when compared to the amount of precipitate in the fully tempered state, the 9Cr-1Mo-V-Nb showed a much greater variation in the degree of precipitation following furnace cooling. In addition, the matrix microstructure of the 9Cr-1Mo-V-Nb alloy was very sensitive to cooling rate. The precipitation reactions during tempering after a normalizing treatment were followed as a function of tempering treatment. Tempering temperatures were varied from 400 to 780 °C. The carbide precipitation was essentially complete after one hour at 650 °C for both alloys. Analytical microscopy was used to identify the precipitates. In the 9Cr-1Mo-V-Nb alloy, a combination of chromium-rich M23C6 and vanadium-niobium-rich MC carbides was found. The carbides in the 12Cr-1Mo-V-W alloy were identified as chromium-rich M23C6 and vanadium-rich MC. The results give an indication of the sensitivity of these alloys to heat treatment variations.

Thermal ink jet printhead

Abstract: A protective passivation structure is provided for a thermal ink jet printing head which employs a resistive heating element formed of phosphorus-diffused silicon. The passivation structure includes a layer of silicon nitride over the heating element with a layer of silicon carbide over the silicon nitride layer. The nitride exhibits good adhesion to the underlying silicon as well as good thermal conductivity. The carbide has exceptionally good wear and hardness qualities against ink bubble cavitation as well as adhering well to the nitride.

Aluminum production cell components

Abstract: An electrolytic aluminum-production cell component, comprising a preformed matrix based on at least one material from the group alumina, aluminum oxynitride, SiAlON, boron nitride, silicon carbide, silicon nitride, aluminum boride and carbides, carbonitrides, boronitrides and borocarbides of metals from Group IVb (titanium, zirconium and hafnium) Group Vb (vanadium, niobium and tantalum)17nd Group VIb (chromium, molybdenum and tungsten) having voids extending throughout its structure, the voids in the preformed matrix structure being filled or substantially filled with aluminum in intimate contact with the matrix.

A study of the ageing behaviour of a cobalt based implant alloy

Abstract: The ageing characteristics of a commercial CoCrMoC alloy were investigated using optical and electron microscopy. Only one phase, the M23C6 type carbide, was positively identified by X-ray and electron diffraction after treatments between 650 and 1175° C for times up to 188 H. Three types of precipitation mechanism were found to operate, the mode of nucleation being dependent upon temperature. At low (< 925° C) temperatures the carbide precipitated on intrinsic stacking faults (hcp cobalt) probably by means of Suzuki segregation. A discontinuous reaction also occurred at grain boundaries in order to assist precipitation, resulting in a lamellar “pearlitic” morphology. At temperatures in excess of 925° C the carbide nucleated and grew on dislocations. This was a result of the increased thermodynamic stability of the f c c cobalt matrix, and the decreasing stacking fault density. Particle coarsening and spheroidisation and agglomeration of the lamellae were also evident. Sharp decreases in ductility associated with ageing precluded any commercial benefit of this type of treatment, despite substantial increases in hardness.

Statistical aspects of cleavage fracture in steel

Abstract: The fracture of mild steel in the cleavage range has been evaluated using a weakest link statistical model, assuming the preexistence of a distribution of cracked carbides. The model provides a rationale for the critical fracture distance, viz., the distance from the crack tip at which the probability of cleavage cracking exhibits a maximum. The critical distance depends on the size distribution and volume fraction of carbides. The model also predicts trends in K,ic with material properties: flow strength, cracked carbide size and volume fraction, and grain size. The resultant temperature dependence of K,ic is shown to derive exclusively from the temperature dependence of the flow stress, as in prior models. The effects of microstructure on K,ic depend primarily on the size distribution of cracked carbides, with additional influences of the grain size and of the volume fraction of carbides.

High temperature hardness of tungsten carbide

Abstract: The effect of crystallographic orientation and test temperature on hardness of WC single crystals was investigated along with the hot hardness of poly crystalline tungsten carbide. Also investigated was the effect of carbide grain size and the amount of binder phase on the hot hardness of some cemented tungsten carbides. The hot hardness of single crystal WC on all major crystallographic orientations evaluated decreases very rapidly for increasing temperature, and the single crystal hardness on its hardest orientation is only about half of the polycrystalline material depending on the test temperature. Because of its polycrystalline character, some cobalt bonded cemented tungsten carbides can be harder than single crystal WC over some intermediate temperature range.

Carburization of steel surfaces during implantation of Ti ions at high fluences

Abstract: Auger and nuclear backscattering analyses of ion‐implanted steels have shown that surfaces implanted with carbide‐forming ions can develop excessively high carbon concentrations well into the implanted layer. A model is presented here in which the residual gases in the vacuum chamber interact with the surface during implantation to carburize the surface. Briefly, (1) implanted Ti ions are ‘‘uncovered’’ by sputtering, (2) they react with residual gases to form surface carbide species, (3) the carbides dissociate, and (4) the carbon atoms diffuse inwards. Composition profiles of steels implanted with Ti ions (5–50×1016/cm2 at 55 and 190 keV) are analyzed and shown to support the model. Carburization occurs at a lower fluence for 55‐keV implants than for 190‐keV implants, consistent with a nearly energy‐independent sputtering yield for Ti into Fe. Implications of the vacuum carburization effects on surface alloy chemistry and mechanical properties are also discussed.

Solid state SiC/Ni alloy reaction

Abstract: The solid state reaction between silicon carbide and a model superalloy consisting of 70 at. pct Ni, 20 at. pct Cr, and 10 at. pct Al was studied between 700 °C and 1150 °C for times ranging from “0” hours to 330 hours. Reaction couples consisting of SiC/Ni, SiC/Cr, and SiC/NiCr were also studied. The reactions were carried out in air with the materials, in the shape of discs, maintained in contact under a pressure of 7 MPa. A reaction was detected with SiC and the model alloy at all temperatures studied, and the reaction was diffusion controlled with an activation energy of 184 kJ/mole. In the ceramic the reaction was dominated by the diffusion of Ni into the ceramic forming a banded structure consisting of alternating layers of δ-Ni2Si and a two phase mixture of graphite and δ. On the metal side, the reaction was very dependent on the presence of alloying elements, with pure Ni reacting to the greatest extent, followed by the binary NiCr alloy, and finally by NiCrAl. The growth and presence of the phases detected in these reactions is consistent with phase equilibria concepts.

Randomly-oriented polycrystalline silicon carbide coatings for abrasive grains

Abstract: Disclosed is a composite abrasive particle comprising a core abrasive crystal and a silicon carbide coating inherently bonded to substantially all of the exterior surfaces of said core crystal, said silicon carbide coating characterized by silicon carbide crystals having a random orientation substantially independent of the structure of the core crystal, the outer surface of the coating being conformationally irregular Aggregates of the composite abrasive particles are interconnected by a matrix of silicon carbide which has an open structure Preferred core abrasive crystals are diamond or cubic boron nitride The composite abrasive particles preferably are made by infiltrating core crystals coated with non-diamond carbonaceous material with fluid silicon to produce a mass of core crystals bonded together by silicon carbide and elemental silicon, leaching substantially all of the silicon from the bonded mass with a silicon leaching agent, sub-dividing the resulting leached mass, and recovering the composite abrasive particles

The Aging and Tempering of Iron-Nickel-Carbon Martensites

Abstract: The aging and tempering of freshly quenched (Ms > RT) and virgin (M < RT) martensites with lath and plate morphologies in Fe-Ni-C alloys have been studied to obtain kinetic and structural information. At subambient temperatures, the first change is attributed to isothermal conversion of a small amount of retained austenite or to slight relaxations in the martensite, but this is not a significant part of the martensite aging process. Aging above -40 °C to about 70 °C is accompanied by the diffusion-controlled clustering of carbon atoms, resulting in an increase in electrical resistivity proportional to the carbon content but independent of the martensitic morphology. This regime is followed above 100 °C by the precipitation of e-carbide (i.e., the conventional first stage of tempering), which may emerge directly from the carbon-rich clusters. At still higher temperatures, cementite forms separately (i.e., the conventional third stage of tempering) in competition with the e-carbide. These two precipitation processes overlap, and their kinetics appear to be controlled by iron-atom diffusion away from the growing carbide particles along dislocation paths. No evidence was found in this investigation for a regime reflecting carbon migration to dislocations or other defects, but this possibility is not ruled out by the experimental methods employed.

Coated carbide cutting tool insert

Abstract: A coated carbide insert has a cobalt enriched zone at one decarburized surface, and a thin TiN transition layer over this surface. The cobalt enriched zone and the TiN layer cooperate to support additional thicker layers of hard wear resistant material such as TiC, TiN, and Al 2 O 3 .

Effect of Composition, Microstructure, and Service Conditions on the Wear of Cemented Carbides

Abstract: A number of different mechanisms account for the wear of cemented carbides. These mechanisms vary with service conditions and with composition and microstructure of the alloy. The main mechanisms are brittle fracture, fatigue, and plastic deformation, possibly assisted to various degrees by corrosion and diffusion. Each of the major mechanisms may act at different levels: (1) the macroscopic level, affecting a major part of the component by the wear event; (2) the microscopic level, affecting a section of material which incorporates a substantial number of grains; and (3) a finer level, where only individual carbide grains or binder areas are affected. These events are discussed, along with effects of microstructure, binder phase metal, carbide type, and binder-carbide bond.

Forming low-resistance contact to silicon

Abstract: Annealing a titanium-rich carbide film deposited on silicon produces, in a single processing step, both a stable titanium silicide contact and a titanium carbide diffusion barrier between the silicide and a subsequently formed overlying layer of aluminum. Reliable low-resistance contacts to VLSI devices are thereby provided in a cost-effective fabrication sequence. Other metallization systems, comprising a silicide and a diffusion barrier to aluminum formed in a single processing step, are also described.

Crystalline defects in M7C3 carbides

Abstract: M7C2, carbides prepared in various conditions have been observed by electron microscopy and diffraction. Examinations of the first-order Laue zone with crystals having the c axis parallel to the electron beam demonstrate that the unit cell describing the structure of these carbides is the orthorhombic cell proposed by Fruchart and Rouault. This cell can be considered as an ordered cell of an average hexagonal cell and can have three orientations at 120° from each other. It contains metal atom tetrahedra whose local environment in prismatic interstices containing carbon atoms is typical and is never destroyed, whatever the conditions of preparation may be. Thus, in primary carbides present in cast irons and steels, the state of crystallization is such that a long-range order of the environment is established : ortho-rhombic domains are separated by {1I00} twins and antiphase boundaries. In Fe7C3 carbides crystallized from amorphous iron-carbon alloys, the local environments are only short...

Carbon-containing sliding layer

Abstract: A workpiece comprises a substrate having a sliding surface provided with a friction-reducing coating. Such coating consists essentially of elemental carbon dispersed in a matrix formed of at least one metallic element in the proportions of 50.1 to 99.1 at % of the elemental carbon and 0.1 to 49.9 at % of the metallic element. The ratio of the metallic element to the elemental carbon differs from the stoichiometric ratio of the carbide.

Diffusion of Silver and Cesium in Silicon-Carbide Coatings of Fuel Particles for High-Temperature Gas-Cooled Reactors

Abstract: Fractional releases of silver and cesium from irradiated silicon-carbide-layered coated particles have been measured during isothermal anneals in the temperature range between 1273 and 1773 K. The release rates measured have been evaluated with the aid of a statistical numerical treatment based on a simple diffusion model in multizone geometry. The resulting diffusion coefficients are described for silver and for cesium. A statistical treatment of the data gives corresponding 95% confidence limits. It is argued that the pathway of cesium and silver transport in silicon-carbide layers is grain boundary diffusion. This explains the large scatter found in the data for coating layers because the defect structure depends on the individual manufacturing conditions and varies from coating to coating. Comparison with data from the literature shows the superiority of silicon carbide with respect to silver retention relative to diffusion rates in pyrocarbons, while cesium data indicate no distinct improvement.

Epsilon carbide: a low-temperature component of interplanetary dust particles.

Abstract: Transmission electron microscope study of a chondritic interplanetary dust particle has revealed the presence of epsilon iron-nickel carbide, a low-temperature carbide previously encountered only in metallurgical studies. In these studies epsilon-carbide was synthesized by carburization of iron or nickel grains in a stream of carbon monoxide or carbon monoxide plus hydrogen. Similar carburization of an iron-nickel metal in situ may have produced epsilon-carbide during particle heating on atmospheric entry or in solar orbit. Alternatively, the epsilon-carbide may be a by-product of Fischer-Tropsch reactions in the solar nebula. Such reactions have been proposed as the mechanism of hydrocarbon formation in the early solar system.

Substantially pore-free sintered polycrystalline articles of α-silicon carbide, boron carbide and free carbon and process for their manufacture

Abstract: The invention provides substantially pore-free sintered polycrystalline articles comprising α-silicon carbide, boron carbide and free carbon, the quantitative proportions of which, in percent by weight, are defined by the trapezoidal area having, in the ternary system B/Si/C of FIG. 1 the corner points a=89.0% B 4 C, 9.9% α-Sic, 1.1% C b=9.9% B 4 C, 89.0% α-SiC, 1.1% C c=9.0% B 4 C, 81.0% α-Sic, 10.0% C d=81.0% B 4 C, 9.0% α-SiC, 10.0% C The articles have a density of at least 99% of the theoretical density, an average structural grain size of less than 20 μm and a 4-point flexural strength of at least 400 N/mm 2 . They are manufactured from fine-grained mixtures of α-silicon carbide, boron carbide, carbon and/or material that can be coked to form carbon, in a two-stage sintering process. In the first stage, green bodies preshaped from the powder are subjected to pressureless sintering to a density of at least 95% TD at from 1950° to 2150° C. In the second stage, the sintered articles are subjected to a post-densification to a density of at least 99% TD, by isostatic hot pressing, without encapsulating, at from 1850° to 2150° C. in a high-pressure autoclave under a gas pressure of at least 10 MPa.