Showing papers on "Carbide published in 1979"

Effect of microstructure on cleavage fracture toughness of quenched and tempered steels

Abstract: The cleavage fracture of quenched and tempered steels at a sharp crack is seen to involve a statistical competition between different sized crack nuclei in the rapidly changing stress gradient ahead of the crack tip. A procedure is proposed, based on this statistical fracture model, whereby it is possible to estimate the cleavage fracture toughness of a steel containing spheroidal carbide particles from a knowledge of the carbide particle radius distribution. Predictions so made are seen to be in good agreement with experimentally determined fracture toughness values over a range of different temperatures and microstructures.

Reactive sputtering of carbon and carbide targets in nitrogen

Abstract: Paracyanogenlike films – (CN)n– are prepared by reactive rf sputtering of carbon in nitrogen. The material is deposited on quartz, silicon, metals, sapphire, and mica from 20° to 450°C. Above 450°C, there is no film accumulation on the substrates. The sputtering process yields a deposition rate greater than ten times the best known commercial method for paracyanogen film preparation. Also described are the results of sputtering carbide targets i.e. HfC, TiC, SiC, in the presence of nitrogen. Due to the stability of the C≡N bond, for example, stoichiometric Si3N4 films unexpectedly were deposited from a SiC target sputtered in N2. Similar results are described for HfC and TiC targets.

Solution treatment behavior of Co-Cr-Mo alloy

Abstract: Current practice in the manufacture of Co-Cr-Mo alloy total hip prostheses is the use of a solution treatment to increase the ductility of the as-cast alloy. This study is concerned with the reactions encountered during solution treatment at temperatures between 1165-1270 degrees C. These reactions, including incipient melting, a carbide transformation from M23C6 to M6C and sigma-phase formation, have been examined using both qualitative and quantitative metallographic techniques, and are shown to influence the production of a single phase microstructure. As a result, an optimum temperature for solution treatment of 1220 degrees C has been determined. It is further proposed that a reduction in the carbon content of this alloy would improve its solution treatment behavior.

The Reduction of Silica with Carbon and Silicon Carbide

Abstract: In the presence of carbon or silicon carbide, silica can be reacted to form a vapor of silicon monoxide. The rates of these reactions were explored at 1300° to 1550°C. For mixtures of carbon and silica, evidence supported a two-step reaction: silicon carbide formed prior to reaction between silicon carbide and silica.

Sintered alpha silicon carbide ceramic body having equiaxed microstructure

Abstract: Pressureless sintered silicon carbide ceramic bodies, having an equiaxed microstructure and an alpha crystalline habit can be produced 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 2250° C., depending on the sintering atmosphere, under conditions such that a coating of carbon source is maintained on the finely divided silicon carbide, and sufficient boron is maintained within the shaped body during firing. Boron can be maintained within the shaped body by various techniques, such as the use of a "seasoned boat" or graphite container for the body being sintered, which has been saturated with boron by exposure to boron at or about the temperature of sintering. There is also disclosed a process for producing a sintered silicon carbide ceramic body, with or without the equiaxed crystal microstructure, from silicon carbide powders of alpha or beta crystal structure, or amorphous noncrystalline silicon carbide, or mixtures thereof.

A study of the early stages of tempering in an Fe-1.2 Pct alloy

Abstract: Mossbauer effect spectroscopy has been used to study changes in the microstructure of an Fe-1.22. wt pct C alloy due to tempering between 373 and 523 K. The orthorhombic transition carbide, η-Fe2C, was identified by transmission electron microscopy and the similarity of ∈-carbide electron diffraction patterns to η-carbide diffraction patterns is noted. Systematic changes in the Mosbauer parameters of martensite and austenite are presented for the various stages of tempering. The same amount of C remains randomly dissolved in the retained austenite throughout tempering and some C is retained in the martensite throughout the range of transition carbide formation. Two sets of Mossbauer parameters corresponding to magnetic phases other than martensite and cementite have been found. These parameters may come from η-carbide, but alternative interpretations are presented.

Carbide coating process by use of molten borax bath in Japan

Abstract: Pore-free and smooth surface carbide layers can be formed on metals and carbon immersed in a molten borax bath above 1073 K. The carbide layers, consisting of VC, NbC, TiC, or Cr7C3, are formed by the reaction between the carbon atoms in the substrate and the carbide forming element atoms dissolved into the fused borax from additive powders such as ironvanadium, ironniobium, iron-titanium, ironchromium, and chromium. Core hardening of steel substrates can be simultaneous or by reaustenitizing after carbide coating. Carbide coated steels show excellent resistance to wear, seizure, corrosion and oxidation. The carbide layers are adherent to the substrate and do not exfoliate in severe service as in cold forming. The process effectively improves performance of dies, tools, machine parts, and is applied in various fields of Japanese industries.

The crystallography of the austenite-ferrite/carbide transformation in Fe−Cr−C alloys

Abstract: This paper establishes the crystallography of the austenite-ferrite/carbide transformation in Cr bearing steels The crystallographic analysis, based on the use of retained austenite in the martensitic phase, is consistent with the oriented nucleation of ferrite in austenite Similarly, it is shown that the nature of the carbide dispersion, which precipitates in association with the transformation, is a sensitive function of the exact austenite/ferrite crystallography

Process for coating a metallic surface with a wear-resistant material

Abstract: The surface of a metallic substrate is coated with wear-resistant material by depositing on the surface a layer of a mixture of a coating powder including a metallic carbide with powdery silicon and heating said layer by exposure to a source of high density energy to bring about simultaneous evaporation of said silicon and fusion of said coating powder with bonding to said substrate. A coating of high surface porosity can be obtained. The substrate may be a piston ring for heavy-duty internal combustion engines.

High strength iron, nickel and cobalt base crystalline alloys with ultrafine dispersion of borides and carbides

Abstract: Alloys, of iron, cobalt, nickel and chromium containing both metalloids and refractory metals are disclosed. The alloys are rapidly solidified at cooling rates of 10 5 -10 7 ° C./sec so as to produce an ultrafine grained metastable crystal structure having enhanced compositional homogeneity. The as-quenched metastable alloys are brittle, permitting pulverization, if desired. Heat treatment is used to convert the metastable brittle alloys into ductile alloys with primary grains of ultrafine grain size which contain an ultrafine dispersion of boride as well as carbide and/or silicide particles. The powders or ribbons can be consolidated into bulk parts. The heat treated alloys possess good mechanical properties, in particular high strength and hardness, as well as good corrosion resistance for selected compositions, making them suitable for many engineering applications.

Observation and atomization energies of the gaseous uranium carbides, UC, UC2, UC3, UC4, UC5, and UC6 by high temperature mass spectrometry

Abstract: Gaseous carbides of uranium, UC, UC2, UC3, UC4, UC5, and UC6 have been observed in a mass spectrometric investigation of the Knudsen cell effusate from a thorium–uranium–rhodium–graphite system at high temperatures. Partial pressures of the carbide molecules were measured as a function of temperature in the 2300–2700° K range. Second and third law methods were employed to determine enthalpy changes for the reactions of the type U(g)+nC(graphite) =UCn(g), n=1 to 6, and for additional reactions with graphite involving two gaseous carbide species and various homogeneous gas phase reactions. The experimental enthalpies when combined with thermodynamic data taken from literature yielded the following atomization energies, ΔH°at,298, and standard heats of formation, ΔH°f,298:

Laser melting and heat treatment of m2 tool steel: A microstructural characterization

Abstract: Microstructural characterization and electron diffraction crystal structure determinations have been carried out on the tool steel M2. Detailed examination using optical microscopy and thin-film and replica transmission electron microscopy substantiate preliminary findings.2,3 Namely, that laser melted material has a two-phase σ-ferrite/austenite matrix containing a dispersion of fine M2C carbides together with a smaller amount of M23C6 carbides. Subsequent heat treatment at 560 and 1230°C increases the hardness (to a maximum value of ∼1100 VHN) by carbide precipitation. In material heat treated at 560°C there is a preponderance of M23C6 carbides together with a small amount of M2C carbides. In contrast, the effect of heat treatment at 1230°C is to produce material containing only MC1-x type carbides with diameters in the range from 20 nm to ∼1 µm.

Friction and Wear Behavior of Single-Crystal Silicon Carbide in Sliding Contact with Various Metals

Abstract: Sliding friction experiments were conducted with single-crystal silicon carbide in contact with various metals. Results indicate the coefficient of friction is related to the relative chemical activity of the metals. The more active the metal, the higher the coefficient of friction. All the metals examined transferred to silicon carbide. The chemical activity of the metal and its shear modulus may play important roles in metal-transfer, the form of the wear debris and the surface roughness of the metal wear scar. The more active the metal, and the less resistance to shear, the greater the transfer to silicon carbide and the rougher the wear scar on the surface of the metal. Hexagon-shaped cracking and fracturing formed by cleavage of both prismatic and basal planes is observed on the silicon carbide surface. Presented at the 33rd Annual Meeting in Dearborn, Michigan, April 17–20, 1978

Influence of carbide thickness on impact transition temperature of ferritic steels

Abstract: A large number of ferrite–pearlite steels have been examined and measurements made of grain size, pearlite volume fraction, degree of precipitation hardening, and thickness of grain-boundary carbid...

Composite of polycrystalline diamond and/or cubic boron nitride body/silicon carbide substrate

Abstract: A shaped confined structure composed of a mass of diamond and/or cubic boron nitride crystals coated with elemental non-diamond carbon in contact with a supporting silicon carbide substrate is infiltrated by fluid silicon producing a like-shaped composite of a polycrystalline body component integrally bonded to the supporting silicon carbide substrate.

Indentation plasticity and microfracture in silicon carbide

Abstract: The extent of the plastically deformed region associated with indentation in silicon carbide is determined by means of selected-area electron channelling. It is found that the extent of the plastic zone beneath an indent is quite large, i.e. equal to about five times the impression radius. Microcrack formation is studied in the SEM, and the combined results are discussed in terms of current elastic-plastic indentation fracture models. The first cracks to form are radial microcracks; their morphology, and the observed indentation plastic zone dimensions, support the elastic-plastic model of Perrott for indentation cracking inα-SiC.

Composite diamond compact for a wire drawing die and a process for the production of the same

Abstract: The present invention relates to a composite diamond compact for a wire drawing die, in which a part or all of the circumference of a diamond sintered body is surrounded by a cermet consisting of a hard compound of (Mo, W)C type carbide crystals containing molybdenum as a predominant component, bonded by an iron group metal, and the binder phase of the diamond sintered body contains an iron group metal and fine carbide crystals containing molybdenum as a predominant component.

Stratified protecting coating for wearing pieces and hard metal cutting tools

Abstract: This invention relates to a hard metal wearing piece, especially for tools, which is covered at least on the places subjected to wear with stratified protecting coating. This stratified protecting coating comprises at least five superimposed layers, at least two of them being of different compositions; furthermore, the internal layer in contact with the substrate is a layer of carbide, the external layer is a layer of boride or carbide, and the intermediary layers are of carbide, nitride, oxide, boride, and/or of mixed compounds thereof.

The melting of boron carbide and the homogeneity range of the boron carbide phase

Abstract: Various mixtures of boron and carbon were electron beam melted. The samples were characterized by electron microprobe analysis, metallographic techniques, X-ray diffraction and Knoop microhardness measurements. The metallographic investigations, together with the electron microprobe phase analysis, showed that the boron carbide phase exists in the homogeneity range 9 – 20 at.% C (with a relative accuracy of 3 – 5%). Boron carbide melts congruently and forms a eutectic between carbon-rich compounds and graphite. For the boron-rich compounds we assumed the existence of a peritectic transformation with a solid solution of carbon in the β rhombohedral boron structure. We studied the crystal lattice dimensions and the microhardness of boron carbide in the above homogeneity range. As the carbon content increased, the crystal lattice dimensions decreased and the microhardness increased regularly with an extreme value of HK200g = 2840 +- 60 kg mm−2 for 20 at.% C (B4C) (after electrolytic etching).

Graded metal carbide solar selective surfaces coated onto glass tubes by a magnetron sputtering system

Abstract: A solar selective absorbing surface consisting of mixed iron, chromium, and nickel carbides on copper has been deposited onto 1.5 m long, 22 mm o.d. glass tubes by reactive and nonreactive dc sputtering. Grading the properties of the metal carbide from metal rich at the copper substrate to dielectric at the surface results in solar absorptances ∠93% and emittances ∠4% at 300 K (both properties averaged along the length of a tube). Aging experiments show that absorptances deteriorate slowly at 300°C in vacuum due to diffusion in the graded film. Emittances at elevated temperature for copper and for the selective surfaces deposited onto tubes have been determined using a calorimetric technique.

Dense sintered shaped articles of polycrystalline α-silicon carbide and process for their manufacture

Abstract: OF THE DISCLOSURE There are provided shaped articles of polycrystalline silicon carbide having densities of at least 97% and improved mechanical properties particularly at high temperatures, said articles consisting of at least 95.4% by weight of .alpha.-silicon carbide, about 0.1 to 2.0% by weight of additional carbon, about 0.2 to 2.0% by weight of aluminium, about 0 to 0.5% by weight of nitrogen, and about 0 to 0.1% by weight of oxygen, the .alpha.-silicon carbide being in the form of a homogeneous micro-structure with an average grain size of less than 10 µm. There is also provided a process for the preparation of such articles by pressureless sintering submicron powder compacts consisting of .alpha.-silicon carbide and aluminium- and carbon containing additives as sintering aids.

Intermediates in CO and CO2 hydrogenation over Ni catalysts

Abstract: The reactivity towards H2 of different species observed during adsorptions of CO and CO2 on Ni/SiO2 catalysts is examined. A mechanism for CO and CO2 hydrogenation on Ni/SiO2 is proposed in which the active carbonaceous species is the “superficial carbide” Ni3Csurf. This mechanism accounts for observed characteristics of CO and CO2 hydrogenation and suggests a possible chain growth via non-oxygenated intermediates.

Friction, Deformation and Fracture of Single-Crystal Silicon Carbide

Abstract: An investigation was conducted to determine the nature of the deformation and fracture of silicon carbide and its effects on friction properties. Friction experiments were conducted with hemispherical and conical diamond riders sliding on the basal plane of silicon carbide. The results indicate that, when deformation is primarily elastic, the friction does not depend on crystallographic orientation and there is no detectable fracture or crocking. When, however, plastic deformation occurs, silicon carbide exhibits anisotropic friction and deformation behavior. Surface fracture crack patterns surrounding wear tracks are observed to be or three types. The crack-geometries of two types are generally independent of orientation, the third crack, however, depends on the orientation. All surface cracks extend into subsurface. Anisotropic friction, deformation and fracture on the basal plane are primary controlled by the slip system {101¯0} ⟨112¯0⟩ and a cleavage of {101¯0}. Presented as an American Society of Lub...