Showing papers on "Carbide published in 1978"

Synthesis of continuous silicon carbide fibre with high tensile strength and high Young's modulus

Abstract: Polycarbosilane as the precursor of continuous SiC fibre was synthesized by thermal decomposition of polydimethylsilane. The structure of the polycarbosilane is concluded to be similar to that of polysilapropylene by the measurements of i.r. spectra, NMR spectra and chemical analyses. Its formation mechanisms are initially the formation of carbosilane by thermal decomposition of polydimethylsilane and then the increase in molecular weight by dehydrogenation-condensation of the carbosilane. Molecular structure and molecular weight distribution of the polycarbosilane depend on the reaction temperature.

Effects of microstructure on cleavage fracture stress in steel

Abstract: It is shown, by compiling data from the literature, that there is a general relationship between the ferrite grain size and the size of the largest carbide particle in mild steels which are simply cooled after austenitization. By using this relationship, a cleavage fracture criterion derived by Smith is shown to predict a grain size dependence for the cleavage fracture stress of mild steel that is in good agreement with the results of many workers. These results indicate a value of 14 J m−2 for the effective surface energy of ferrite.Experimental results are presented showing the variation of the cleavage fracture stress of spheroidized steels with carbide particle radius. These support the suggestion that cleavage in such steels is due to the propagation of penny-shaped crack nuclei prod uced when spheroidal carbide particles crack. If the 95th percentile carbide radius is taken to represent the crack nucleus radius, an effective surface energy value of 14 Jm−2 is found to satisfy the fracture st...

Composite compact of interleaved polycrystalline particles and cemented carbide masses

Abstract: One or more masses of bonded particles of diamond, cubic boron nitride (CBN), and wurtzite boron nitride (WBN) are sandwiched between or encapsulated by two masses of cemented carbide bonded to the particle masses. In the preferred embodiment, the particle masses are comprised of (1) at least 70% by volume of said particles, and (2) a metallic phase comprised of the cementing agent of the carbide mass. The composite compacts find utility in drill bit, mining tool and wear part applications. A method for making such a composite compact comprises (1) placing within a reaction cell masses of abrasive particles and at least two carbide masses interleaved with the abrasive particle masses, (2) the masses are placed in the cell in such a manner to allow for the accommodation of pressure and (3) simultaneously subjecting the cell and the contents thereof to temperature and pressure conditions at which the particles are stable. A method for abrading or cutting a workpiece with a composite compact comprises providing (1) a tubular carbide mass and a bonded mass of abrasive particles disposed in and bonded to the carbide mass in a central cavity thereof and (2) moving either the compact or workpiece relative to the other to provide the cutting or abrading action.

High-temperature corrosion and creep of Ni-Cr-Fe alloys in carburizing and oxidizing environments

Abstract: The carburization of NiCr 32 20 and NiCrSi 60 16 has been studied in CH4-H2 mixtures in the temperature range 900–1100°C. The methods included thermogravimetric measurements and studies on reacted specimens by X-ray diffraction, metallographic, and chemical analysis. Upon carburization internal carbides M7C3 and M23C6 are formed (M=mainly Cr); the rate of carburization is determined by carbon diffusion in the Fe-Ni matrix with carbide precipitations. The effect of the alloying elements Ni and Si on the carburization resistance of austenitic alloys is explained. By the same methods the oxidation and carburization in CO-H2O-H2 mixtures have been studied. The important role of a stable chromium oxide layer for the carburization resistance was confirmed. Creep tests at 1000°C in a CO-H2O-H2 atmosphere where Cr2O3 is stable showed carburization occurring through cracks in the oxide layer. At high strain rates premature failure occurs by carburization, which is followed by internal oxidation and formation of cracks, voids, and holes.

Microstructural characterization of ?REFEL? (reaction-bonded) silicon carbides

Abstract: Quantitative characterization of the microstructure of a number of samples of reactionbonded (REFEL) silicon carbide has been undertaken employing transmission and scanning electron microscopy, optical microscopy, and electron and X-ray diffraction techniques. Impurity-controlled secondary electron SEM image contrast has proved particularly useful in differentiating between the SiC present in the initial compact and that formed during the reaction-bonding process, and, in contrast to previous descriptions of the microstructure, it has been found that the newly-formed SiC is deposited from the supersaturated solution of carbon in molten silicon both epitaxially on the original SiC grains, maintaining the sameα-polytypic stacking sequences, and by nucleation of fine cubicβ-SiC elsewhere. The relative quantities of material occurring by these two mechanisms have been found to vary from sample to sample, although the epitaxial growth on the original grains always occurs to some extent and is responsible for the bulk cohesion of the material. Some conclusions have been drawn concerning the reaction model and the process parameters controlling the microstructure of this type of material.

Precipitation of carbides in low-carbon Fe-AI-C alloys

Abstract: High-purity Fe-C alloys containing up to 5.8 pct Al were quenched from 730°C, then aged at temperatures up to 400°C. Precipitation of a carbide transition phase (presumably e) and of cementite were followed by transmission electron microscopy, coercive force measurements, and changes in yield strength. The presence of aluminum increases the temperature at which cementite begins to precipitate during aging. This effect is similar to that produced by silicon in ferrite, and opposite to that produced by manganese. It is suggested that the effects of Si, Mn, and Al on cementite precipitation from ferrite arise from the effects of these elements on the stability of cementite, as reflected in the equilibrium partition of carbon between cementite and ferrite.

An XPS study of the adherence of refractory carbide silicide and boride rf‐sputtered wear‐resistant coatings

Abstract: Radio frequency sputtering was used to deposit refractory carbide, silicide, and boride coatings on 440-C steel substrates. Both sputter etched and pre-oxidized substrates were used and the films were deposited with and without a substrate bias. The composition of the coatings was determined as a function of depth by X-ray photoelectron spectroscopy combined with argon ion etching. Friction and wear tests were conducted to evaluate coating adherence. In the interfacial region there was evidence that bias may produce a graded interface for some compounds. Biasing, while generally improving bulk film stoichiometry, can adversely affect adherence by removing interfacial oxide layers. Oxides of all film constituents except carbon and iron were present in all cases but the iron oxide coverage was only complete on the preoxidized substrates. The film and iron oxides were mixed in the MoSi2 and Mo2C films but layered in the Mo2B5 films. In the case of mixed oxides, preoxidation enhanced film adherence. In the layered case it did not.

Effect of solidification parameters on the growth geometry of MC carbide in IN- 100 dendritic monocrystals

Abstract: Several dendritic monocrystals of IN-100 were prepared under six growth conditions with thermal gradient,G, varying between 4.5 × l03 and 16 × 103 K/m and growth rate,R, be-tween 8.3 × 10-6 and 67 × 10-6 m/s. Three types of carbide were identified: the unmelted, the faceted and the Chinese script-type. The volume percent of faceted carbide increased with increasingG/R ratio whereas that of the Chinese script-type exhibited the inverse variation. The average faceted carbide size and the average spacing of the Chinese script-type carbide decreased with increasing cooling rate, (G ×R), The specific perimeter of the faceted carbide increased with increasing cooling rate, indicating that coarsening is responsible for final geometry of this carbide. Detailed composition measurements showed that the unmelted carbide is rich in titanium, whereas the faceted is rich in mo-lybdenum and vanadium.

Hardfacing composition of nickel-bonded sintered chromium carbide particles and tools hardfaced thereof

Abstract: A mining or drilling tool which has a region subject to excessive wear is hardfaced on such region with sintered chromium carbide particles metallurgically bonded on the tool by a steel matrix which is alloyed with the particles at the interfaces therebetween. The particles are in a size range of 10 to 60 mesh and are present in an amount for effective abrasion resistance. The particles are comprised of grains of chromium carbide having an average size in the range of 0.5 to 25 microns disposed in a binder comprising a major portion of nickel. Minor portions of grain growth inhibitors, particularly, tinanium carbide and molybdenum carbide, are preferably components of the carbide particles so as to inhibit growth of the chromium carbide grains to be such that such grains have an average size in the range of 0.5 to 15 microns. The particles are preferably coated, prior to being applied as the hardfacing, with one or more materials such as ferrosilicon, ferromanganese, ferromolybdenum, nichrome and others identified below, to limit the alloying of the particle per se with a steel matrix, to improve the matrix, and to improve the welding characteristics of the hardfacing materials. There is also provided material comprising discrete particles as above described which are useful in forming the hardfacing material on the tool.

Fracture of aluminium-coated carbon fibres

Abstract: A degradation in the ultimate tensile strength (UTS) of aluminium-coated carbon fibres was associated with the formation of a reaction layer of aluminium carbide during annealing treatments ⩾ 475° C for high tensile fibres (HT) and ⩾ 550° C for high modulus fibres (HM). It was established that for a given annealing treatment, the UTS depended on the square root of the original coating thickness and proposed that fracture was controlled by cracks in the aluminium carbide, with a specific surface energy (γ) and intrinsic crack length (c0) of 2.33 J m−2 and ∼ 30 nm for HT fibres, and of 0.64 to 0.77 J m−2 and ∼ 20 nm for HM fibres.

The compression creep behaviour of silicon nitride ceramics

Abstract: A comparison has been made of the compression creep characteristics of samples of reaction-bonded and hot-pressed silicon nitride, a sialon and silicon carbide. In addition, the effects of factors such as oxide additions and fabrication variables on the creep resistance of reaction-bonded material and the influence of dispersions of SiC particles on the creep properties of hot-pressed silicon nitride have been considered. For the entire range of materials examined, the creep behaviour appears to be determined primarily by the rate at which the development of grain boundary microcracks allows relative movement of the crystals to take place.

Wear resistant coated article

Abstract: A brake rotor with a ceramic-metallic coating. The ceramic-metallic coating provides a wear resistant surface. The coating generally comprises about 30 to 70% by weight of ceramic particles in about 30 to 70% by weight metallic carrier material compatible with the substrate and carbide.

Coated cemented carbide body and method of making such a body

Abstract: COATED CEMENTED CARBIDE BODY AND METHOD OF MAKING SUCH A BODY Abstract of the Disclosure There is disclosed a sintered cemented carbide body containing at least one carbide besides binder metal, on which body there is applied at least one thin, wear resistant surface layer essentially consisting of aluminium oxide. The aluminium oxide to at least 85% consists of the kappa modification, the remainder, which mainly constitutes the alpha modification, being formed as surface portions or spots having a size of at the most 10 µm, the relationship between the size and the occurrence of the alpha form aluminium oxide spots being within the area AOBC in Fig. 1 of the attached drawing. The body is made by a method wherein a cemented carbide substrate is contacted with a gas containing an aluminium halide and a re-ducing agent at high temperature, characterized in that a dopant addition of tetravalent titanium, zirconium and/or hafnium ions is added to the gas in an amount of 0.03 to 0.5% of the totally supplied amount of gas.

Low Temperature Sensitization of Welded Type 304 Stainless Steel

Abstract: It has been shown that the sensitization of Type 304 stainless steel occurs at temperatures well below the normal isothermal temperature range for sensitization. A prerequisite for this low temperature sensitization (LTS) is the presence of chromium carbide nuclei along grain boundaries. This paper shows that the thermal exposure during welding can nucleate the grain boundary carbides necessary for subsequent LTS. Quantitative transmission electron microscopy studies show that no new carbides nucleate during an LTS heat treatment at 400 C. However, carbides that were nucleated at the time of welding grow during the LTS heat treatment. These findings are consistent with the proposed nucleation and growth LTS model. Using an accelerated test for intergranular stress corrosion cracking (IGSCC) in high temperature, high purity, 8 ppm oxygen water, it has been found that the rate of LTS in a Type 304 stainless steel weld heat affected zone obeys an Arrhenius temperature dependence which predicts that ...

Hydrogen Diffusion and Solubility in Silicon Carbide

Abstract: Tritium diffusion coefficients and deuterium solubilities were measured for silicon carbide. At 500 to 1300/sup 0/C, measured tritium diffusion coefficients were much lower than the recorded values for metals, whereas the activation energies for diffusion were much higher (30 to 75 kcal/mol). The solubility of deuterium in silicon carbide decreased as temperature increased and exhibited a pressure dependence of approx. =P/sup 1/2/.

Microstructural changes which occur during isochronal heat treatment of the nickel-base superalloy IN-738

Abstract: The microstructure of the cast superalloy IN-738 has been analysed after isochronal heat treatments (16 h) within the temperature range 773 to 1467 K. The effect of such heat treatments on the morphology, distribution and volume fraction of bothγ′ and carbide precipitates has been established and correlated with changes in the hardness. These measured hardness changes are discussed in relation to the contributions ofγ′ precipitation hardening and matrix solid solution hardening.

Tungsten carbide powders produced by the vapor phase reaction of the WCl6-CH4-H2 system

Abstract: Black powders of tungsten carbides (WC, W2C), including tungsten metal, were produced by the vapor phase reaction of the WCl6-CH4-H2 system at 1000–1400 °C. The C/W ratio of the product increased sharply with increasing reaction temperature and increasing methane concentration. At 1400 °C the product consisted of almost pure WC. The particle size of the carbide powders, which was significantly influenced by the mixing temperature of WCl6 and H2, was 0.04–0.05 μm for low mixing temperatures and 0.08–0.11 μm for high mixing temperatures. The formation of tungsten carbide powders in this reaction system was found to occur in two steps, namely the initial formation of W particles and their subsequent carburization. This was confirmed by separate examinations of the hydrogen reduction of WCl6 and the carburization of W powders with methane.

Strength improvement of cemented carbides by hot isostatic pressing (HIP)

Abstract: HIP treatment after sintering increases the strength of the investigated cemented carbide alloy by a factor of two whereas hardness, fracture toughness, and work of fracture remain unchanged. HIP does not affect the microstructural parameters of the carbide skeleton and the binder phase, but the residual pores are eliminated entirely. Failure of both the as-sintered and post-densified material occurs by a pure Griffith mechanism. The strength-flaw size relationship is established experimentally and is shown to obey exactly Griffith's basic strength equation. The strength is controlled by the largest microstructural defects, i.e. pores in the as-sintered material, and coarse WC grains and inclusions in the HIP-treated specimens.

Flexible bilayered sheet, one layer of which contains abrasive particles in a volatilizable organic binder and the other layer of which contains alloy particles in a volatilizable binder, method for producing same and coating produced by heating same

Abstract: A flexible sheet of a top layer of nickel brazing alloy particles overcast on a tapecast base layer of tungsten carbide particles, the brazing alloy particles and carbide particles each dispersed in and supported by an organic binder matrix, when placed on a substrate dewaxed and heated to about 1100° C., forms a braze infiltrated hardfacing coating of tungsten carbide particles in a braze alloy matrix, which coating is metallurgically bonded to and enhances the hardness and wear resistance of the coated substrate.

Method of making molten silicon infiltration reaction products

Abstract: Infiltration reaction products are provided of molten silicon and certain blends of particulated carbon and various particulated inorganic materials substantially unreactive to molten silicon, such as boron nitride particles. These molten silicon infiltration products of reaction are readily machinable and can be applied, or formed in-situ as contiguous layers on silicon carbide, or silicon-silicon carbide substrates, etc., to produce multilayer composites having an improved impact strength over the base refractory structure.

Coated particles and process of preparing same

Abstract: Novel powders, and resinous compositions bearing said powders, characterized by excellent chemical stability, electrical conductivity, and energy-absorbing characteristics. These three characteristics can be utilized, alone or combination, in forming many novel articles including microwave shielding apparatus, magnetic recording media, explosives, and the like articles. The more advantageous powders are characterized by a very thin coating of an electrically conductive metal carbide, metal silicide, or metal boride upon the surface thereof, and a metal core.

Preparation of Pure and Doped Silicon Carbide by Pyrolysis of Silane Compounds

Abstract: Polycrystalline is prepared from three different silane compounds (methyl‐trichlorosilane, dimethyl‐dichlorosilane, and trimethyl‐chlorosilane) by the van Arkel process. The influence of the growth parameters (flow rates, vapor pressures, and deposition temperature) on the growth rate and the stoichiometry of the deposit is investigated. The most satisfactory results in terms of stoichiometry are obtained in the 1400°–1600°C temperature range. Doping is accomplished by adding trimethyl‐aluminum and diborane. The 6H silicon carbide crystals are grown by the sublimation technique using doped and undoped polycrystalline material.