Showing papers on "Carbide published in 1975"

Continuous silicon carbide fiber of high tensile strength

Abstract: Continuous silicon carbide fiber of high-tensile strength (about 350 Kg/mm2) was synthesized by means of the heat-treatment of organosilicon polymer obtained from dodecamethylcyclohexasilane. X-ray analysis and high voltage electron microscopic observations revealed that the obtained continuous fiber is an ultrafine grain structure of β-silicon carbide.

The crystal structure of a boron-rich boron carbide

Abstract: Structural changes accompanying extreme boron-enrichment of boron carbide were deduced with Mo K0¢ X-ray diffraction data obtained from a twinned aggregate containing a minimal amount of carbon. The crystal system remains rhombohedral, probable space group R-3m, as for B4C, but unit-cell parameters show significant expansions compared to those of a 20 at. % C material. Fourier, difference Fourier, and least-squares calculations produced a final weighted R value of 9"04 % and a al of 0"985 for a structure that retains (BI~) icosahedra and randomly replaces about one fourth of the [CBC] chains with [B4] groups. Terminal atoms of the latter are fixed along a threefold axis and have fivefold coordination, being bonded to two central (or bridge) atoms of the group and to three icosahedral atoms. Bridge atoms lie in two of twelve equivalent positions near a plane normal to the threefold axis; they also have fivefold coordination, being bonded to the two terminal atoms of the group and to three icosahedral atoms. The chemical composition of the proposed structure, 9-7 at.% C, agrees with published phase diagrams, but exceeds the analyzed carbon contents of 4.8 at. % C (bulk chemical analysis) and 8 at. % C (ion microprobe analysis). Possible reasons for the location of the boron-rich terminus of the boron carbide phase field are discussed in view of the proposed structure.

On the Deformation of WC–Co Cemented Carbides

Abstract: The deformation characteristics of WC–Co cemented carbide composites, with emphasis on the binder phase, were investigated. The binder, which is present mainly in the fcc modification in the as-sintered condition, was found to deform through the formation of hcp lamellae. This initially gives the binder the ability to deform in full compatibility with the carbide skeleton. Ultimately the partially transformed binder is unable to fulfil the compatibility requirements and loses its ability to impede crack propagation. Simultaneously the carbide skeleton, which deforms plastically by a glide mechanismin each WC grain, starts to break up and fracture of the composite occurs.

Crack propagation and fracture in silicon carbide

Abstract: Fracture mechanics and strength studies performed on two silicon carbides — a hot-pressed material (with alumina) and a sintered material (with boron) — have shown that both materials exhibit slow crack growth at room temperature in water, but only the hotpressed material exhibits significant high temperature slow crack growth (1000 to 1400‡ C). A good correlation of the observed fracture behaviour with the crack growth predicted from the fracture mechanics parameters shows that effective failure predictions for this material can be achieved using macro-fracture mechanics data.

Structural analysis in continuous silicon carbide fiber of high tensile strength

Abstract: The starting material of a continuous silicon carbide fiber with very high tensile strength is a polycarbosilane. It begins to decompose from 300°C in vacuum and is gradually converted into a β-silicon carbide fiber by the heat-treatment at the temperature above 800°C.

Cast microstructure of Inconel 713C and its dependence on solidification variables

Abstract: The dependence of cast microstructure of Inconel 713C on solidification variables was investigated over a wide range of local cooling rates, ∈, and thermal gradients in the liquid at the solid-liquid interface,G. The shape of MC carbide particles was found to depend greatly on: 1) theG/R ratio at the solid-liquid interface, whereR is growth rate, through the effect of this ratio on the solid phase,γ γ , growth morphology. Under planar front growth conditions the carbide particles were octahedral, under cellular growth conditions they were plate-like, elongated along the cellular growth direction, and under dendritic growth conditions they were irregularly shaped; 2) the local cooling rate, ∈, when γ was dendritic, with a transition from octahedral to dendritic with increasing ∈. The size of MC carbide particles was found to be controlled by coarsening and to become finer with increasing ∈. In this alloy the composition of the MC carbide was established as (Nb0.63Ti0.31Mo0.06) C and was practically independent of local cooling rate. Other observations were that the precipitation of γ′ and the formation of nonequilibrium eutectics, such as MC-γ, γ-γ′ or MC-γ-γ′ were suppressed at splat-cooling rates. Also, microsegregation of all alloying elements with the exception of aluminum was normal, with concentration increasing from the dendrite center-line to the dendrite arm boundary. Aluminum behaved in the opposite manner. Within the cooling rate range used herein, this variable had only a slight effect on microsegregation.

Microstructural stability of titanium-modified type 316 and type 321 stainless steel

Abstract: Optical metallography, transmission electron microscopy, and X-ray diffraction from bulk extracted residues were used to investigate the microstructural stability in the temperature range 450°C to 950°C of a titanium-modified type 316 stainless steel and to compare this steel to a type 321 heat. The effect of cold deformation prior to aging was also investigated. Compared to standard type 316 stainless steel, the nucleation of M23C6 was delayed and its growth retarded in the titanium modified alloy due to early formation of TiC and Ti4C2S2 which reduced the carbon content in the matrix. Precipitation of the intermetallic σ and χ phases was faster in the titanium modified alloy. The type 321 material formed both M23C6 and the intermetallic phases less rapidly than either standard or titanium-modified type 316 steels. The relative tendencies toward intermetallic compound formation in various austentic stainless steels are discussed in terms of an “effective equivalent Cr content” remaining in the austenitic matrix after carbide precipitation. Cold work accelerated the precipitation rate of M23C6 and σ, but it suppressed χ formation due to preferential early σ formation. Early sigma formation was often associated with recrystallization of the cold worked matrix. Mechanisms accounting for this behavior are discussed.

Sintered cemented carbide body coated with three layers

Abstract: A triple coated cemented hard metal carbide product in which a cemented metal carbide substrate is coated with, first, a metal carbide coating, in such a manner so as to create a carbon deficient area in the substrate, then, a metal carbo-nitride and, finally, a metal nitride coating so as to take advantage of the metal carbide and metal nitride properties in order to protect the cemented metal carbide substrate from corrosive atmospheres and abrasion due to frictional wear.

Preparation of finely-divided refractory powders of groups III-V metal borides, carbides, nitrides, silicides and sulfides

Abstract: The preparation of metal and metalloid carbides, borides, nitrides silicides and sulfides by reaction in the vapor phase of the corresponding vaporous metal halide, e.g., metal chloride, with a source of carbon, boron, nitrogen, silicon or sulfur respectively in a reactor is described. Reactants can be introduced into the reactor through a reactant inlet nozzle assembly. Inhibition and often substantial elimination of product growth on exposed surfaces of such assembly is accomplished by introducing the corresponding substantially anhydrous hydrogen halide, e.g., hydrogen chloride, into the principal reactant mixing zone.

The Secondary Hardening of Tungsten Steels

Abstract: The tempering characteristics of a steel with 2 at.−%W 1.1 at.−%C in the range 500–700°C have been studied and structural changes related to the secondary-hardening phenomenon. The sequence of carbides found both at grain boundaries and in the matrix has been established,and detailed structural observations have been made on the nucleation of W2C and M6C. The ageing behaviour is contrasted with that of a comparable molybdenum steel in which the carbide reactions occur more rapidly. Trace additions of Nb Ti and Ta improve the basic strengthening reaction by providing a fine secondary carbide dispersion which also inhibits the coarsening of the dislocation network. The main carbide dispersion is also refined.

Process for coating inorganic substrates with carbides, nitrides and/or carbonitrides

Abstract: A process for coating inorganic substrates, especially metallic or metalloid substrates, sintered metal carbides and carbon materials with carbides, nitrides and/or carbonitrides, using certain nitriles as sources of carbon and nitrogen, is described. High deposition rates and smooth coatings of good to very good adhesion are achievable by this process.

Modifying the surface of diamond particles

Abstract: Abrasive particles are prepared by milling diamond particles, metal compound and milling balls to smear a coating of the compound on the diamond particles and firing the compound-coated diamond particles producing a rough granular adherent covering of metal and/or metal carbide surface coating chemically bonded to the diamond surface by metal carbide.

A Thermodynamic Evaluation of Carbide Solubilities in the Fe–Mo–C, Fe–W–C, and Fe–Mo–W–C Systems at 1000°C

Abstract: The equilibria involving carbides and ferrite or austenite in the systems Fe–Mo–C, Fe–W–C, and Fe–Mo–W–C have been studied at 1000°e, using carefully selected alloys and well-controlled heat treatm...

Hard metal body and its method of manufacture

Abstract: A wear-resistant hard metal body is provided including a core of a hard metal body and a surface coating of a hard material on the core. The core of hard metal body includes at least one of the binder metals iron, cobalt and nickel and at least one of the carbides of the elements titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum and tungsten. The surface coating of hard material contains at least one carbide, nitride, boride and/or oxide. The binder metal contained in the core of hard metal body is also contained in the surface coating of the hard material and originates from the core of hard metal body. A method is provided for producing such wear-resistant hard metal bodies by subjecting a hard metal body comprising a core of hard metal body and a hard surface coating on the core to a pressure of between about 10 - 5 Torr and about 10 bar and a temperature between about 900° and about 1600° C for a period of time between about one minute and about 8 hours to diffuse binder metal from the core into the surface coating.

The composition of eta carbide phase in 2 1/4 Cr-1 Mo Steel

Abstract: The metal-to-carbon ratio in the eta phase in 2 1/4 Cr-1 Mo steel exposed to sodium at 566°C for 26,500 h, and probably under a variety of service conditions, approaches four, rather than six, a fact which may be influenced by the presence of Si, O, and perhaps Cr. Silicon is present in the eta phase, probably on a metal sublattice, while oxygen is probably present on the metalloid sublattice. The observation is supported by both structural and compositional data from the literature.

Process for the production of tungsten carbide or mixed metal carbides

Abstract: A process for the production of tungsten carbide or mixed metal carbides, which comprises mixing tungsten oxide powder of mixed high melting point metal oxide powders with carbon powder in an amount sufficient to form the corresponding carbide, heating the mixture at a temperature of higher than 1000° C in an inert atmosphere or in vacuum to reduce the oxygen content and then heating at a temperature of higher than 1400° C in hydrogen atmosphere, thereby to form tungsten carbide or mixed metal carbides directly from the corresponding oxide.

Susceptibility of Cr-Ni-Mn Stainless Steels to Pitting in Chloride Solutions

Abstract: Anodic behavior of 18Cr-5Ni steels containing 0.03 to 15% Mn was studied in 0.1N H2SO4 solution with additions of 0.01 to 0.1N NaCl. The presence of 5.7 to 15% Mn in those steels decreases their ability to passivate and their resistance to pitting. The most susceptible locations for pit nucleation are boundaries between the austenite matrix and the carbide particles. The pitting resistance of chromium-nickel-manganese steels is discussed with respect to their phase compositions.

Cemented carbides containing hexagonal molybdenum

Abstract: A composition of material is disclosed which comprises sintered carbide-binder metal alloys. The carbide is a solid solution of hexagonal tungsten monocarbide and molybdenum monocarbide of stoichiometric composition containing between 10 and 100 mole percent molybdenum monocarbide. The binder is selected from the metals of the iron group, and comprises between 3 and 50 weight percent of the composition. A method for making the hexagonal carbide is also disclosed.

Sintered silicon carbide ceramic body

Abstract: Pressureless sintering of silicon carbide to produce ceramic bodies having 75% and greater theoretical densities, can be accomplished by firing shaped bodies, containing finely divided silicon carbide, boron source such as boron carbide, carbon source such as phenolic resin and a temporary binder, at a sintering temperature of from about 1900° C. to about 2500° C.

Weldable coated steel sheet

Abstract: A weldable coated steel sheet comprising a steel sheet substrate and a paint coating layer thereon, said paint comprising at least one of the group consisting essentially of titanium carbide, zirconium carbide, hafnium carbide, vanadium carbide, niobium carbide, tantalum carbide, and chromium carbide in the powder form.

The High-Temperature Oxidation of Hot-Pressed Silicon Carbide

Abstract: For the past several years, we have been studying the oxidation behavior of a number of silicon-based materials, the aim being to define the rate-determining mechanism of oxidation. These materials have a bright future in high-temperature energy systems such as MHD generators, rocket engines, re-entry vehicles, and advanced air-breathing propulsion systems. Desirable properties include retained strength at elevated temperatures, chemical inertness, thermal stability, and high strength-to-weight ratio.

Atom-Probe Field-Ion Microscopy of Mixed Vanadium–Titanium Carbides in a Low-Alloy Steel

Abstract: The compositions of carbide particles which precipitate during the isothermal transformation of a low-alloy steel containing both V and Ti have been investigated by atom-probe field-ion microscopy. The carbides were found to have a mixed (V, Ti)C composition and, following their initial precipitation, contained a small quantity of Fe. This disappeared on subsequent long-term ageing. Analysis of relatively large particles produced by long-term ageing showed them to have the approximate chemical formula (V0·45Tio·55)Co·84. It is suggested that this may be the composition of an ordered compound, having an increased binding energy, which previous evidence suggests to exist.

An analysis of the decarburization and aging processes in 2 1/4 Cr−1 Mo steel

Abstract: Specimens of 2 1/4 Cr−1 Mo steel that had been decarburized in sodium or aged in an inert atmosphere for 26,500 h at 839 K were metallurgically examined with optical and transmission electron microscopy The carbide particle density of the decarburized and aged specimens was considerably less after 26,500 h than after 10,000 h, with the density in the aged specimen being considerably greater than that in the decarburized specimen For the aged specimen, the density decrease was a result of Ostwald ripening, and the total amount of carbide was not noticeably affected Decarburization, however, resulted in a gradient in carbide density, with the smallest density near the surface Carbides were electrolytically extracted and identified by X-ray diffraction From the before-test material, which was in the annealed condition and had a ferrite-pearlite microstructure, 14 wt pct carbide was obtained This sample contained M3C, M23C6, and M6C, with M23C6 constituting the major portion In the aged specimen, 23 wt pct of precipitate was extracted and contained 60 pct M6C, the balance M23C6 The decarburized specimen contained two regions with different carbide contents The first 20 pct of the 16 mm thick (0063 in) specimen yielded 13 wt pct precipitate, which contained 94 pct M6C, the balance M23C6 The interior of the specimen contained 16 wt pct precipitate, 86 pct M6C