Showing papers on "Carbide published in 1972"

Phase instabilities during high temperature exposure of 316 austenitic stainless steel

Abstract: Although Type 316 austenitic stainless steel is widely used in steam generating plants and nuclear reactors the knowledge about aging reactions, nature of precipitates, and precipitation kinetics during high temperature exposure is limited. Time-temperature-precipitation (TTP) diagrams were determined between 400° and 900°C for up to 3000 hr as a function of carbon content, solution treatment temperature, and cold work. The nucleation and growth phenomena, morphology, and composition of the various carbide (M23C6, M6C) and intermetallic phases (σ, χ, η were determined. The complex sequence of phase instabilities can be explained on the basis of the carbon content, effect of molybdenum and chromium on the carbon solubility, thermodynamic stability of the phases, and the kinetics of the various precipitation reactions.

A debate on the bainite reaction

Abstract: The authors debate three topics central to the controversies which have enveloped the bainite reaction ever since it was first recognized as a distinctive mode of austenite decomposition. These include: “what is bainite?”, “the growth mechanism of the ferritic component of bainite”, and “the sources of bainitic carbide precipitation.” RFH concludes that bainite is the product of a shear transformation. Individual bainite plates are suggested to grow substantially more rapidly than volume diffusion-control allows, but a constraint such as the build-up of volume strain energy limits the extent of their growth. This mechanism of growth ensures extensive supersaturation of bainitic ferrite with respect to carbon. Whether or not carbides precipitate in association with bainite plates and whether the carbide is cementite ore, however, is a complex question in competitive reaction kinetics. New experimental evidence is presented to demonstrate thate carbide precipitated in lower bainite dissolves upon heating above the kinetic-B stemperature in an alloy steel containing 1.5 pct Si. This result is taken to support the existence of the metastable eutectoid reactionγ ⇌ α + e atca 350°C. HIA and KRK define bainite as the product of a nonlamellar eutectoid reaction. On this view, carbide precipitation thus plays an essential, rather than an ancillary role. Development of the Widmanstatten morphology by the ferritic component of bainite is shown to be inessential to the classification of a eutectoid structure as bainite. When this morphology is present, however, it is concluded to grow by the ledge mechanism, without the participation of shear, at rates of the order of or less than those allowed by volume diffusion-control. New experimental evidence is presented to show that the lengthening and thickening kinetics of individual plates within sheaves of upper bainite are consistent with this description. The results of a new calculation indicate that the initial carbon content of bainite plates lies between theα/α + Fe3C) and the extrapolatedα/(α+ γ) phase boundaries, in agreement with expectation from the ledge mechanism of growth.

Activated Reactive Evaporation Process for High Rate Deposition of Compounds

Abstract: Activated reactive evaporation is a new process developed for the high rate deposition of compounds. It circumvents problems associated with direct evaporation of compounds. Metal vapors from high rate evaporation sources are reacted with a gas in the vapor phase to form and deposit compounds. The vapor phase reaction has to be activated by ionization of the reacting species, i.e., metal vapor and gas in the reaction zone. The steps of compound synthesis and compound deposition are thus separated. Control of deposit stoichiometry, e.g., [C/M] ratio for TiC synthesis is readily achieved by controlling the relative amounts of reactants. Results on the synthesis of carbides, oxides, and nitrides are presented.

Microstructural development during the liquid-phase sintering of cemented carbides

Abstract: Measurements have been made of the contiguity, the dihedral angle, and the continuity of the carbide phase in alloys of a number of transition-metal carbides with cobalt, which were prepared by liquid-phase sintering. During sintering, the carbide contiguity in a given alloy develops towards an equilibrium value, which is directly related to the dihedral angle between carbide grains and therefore to the relative values of the interfacial energy and the contiguous boundary energy. A direct relationship between the contiguity and the angle of contact of the liquid on the carbide, however, does not exist. The contiguity at the start of sintering depends to some extent on the history of the specimen before liquid-phase sintering and in most cases is higher than the equilibrium value. Observations were made which indicate that the carbide grains in the majority of cemented carbides exist as a continuous skeleton. Arguments are presented to show that neither the presence of such a skeleton nor the prese...

Activity of carbon and solubility of carbides in the FCC Fe-Mo-C, Fe-Cr-C, and Fe-V-C alloys

Abstract: The activity of carbon in austenitic Fe-Mo-C, Fe-Cr-C, and Fe-V-C alloys has been studied by equilibration with controlled CH4-H2 atmospheres at temperatures in the range 850° to 1200°C. The observations included a number of compositions in the two-phase fields, γ + carbide. Equations are given for the activity coefficient of carbon as a function of temperature and composition in the austenite field and from these the other thermodynamic properties of the solution may be computed as desired. The phase boundaries γ/γ + carbide were determined by breaks in the isoactivity lines. This was supplemented in the case of Fe-Mo-C alloys by metallographic linear analysis of equilibrated samples. The results confirm certain published phase diagrams and discredit others.

Ion plating method and product therefrom

Abstract: An ion plating method and product therefrom wherein ions of a metal are implanted into or/and plated onto a substrate to increase the hardness of the surface. After plating, the product can be reacted with carbon, boron, nitrogen or another metal, thereby forming the carbide, boride, nitride or metal compound of the plating metal coating. Hardening of the product by quenching follows which produces a cutting tool of superior qualities.

Impacting tool with tungsten carbide insert tip

Abstract: An impacting tool in which a massive hard carbide element is fitted to a steel holder which is reciprocated to drive the element against a formation to be broken. The massive carbide element can be press fitted in the steel holder or shrink fitted therein or brazed thereto and, furthermore, the carbide element can be fitted to a steel sleeve adapted for being secured to a steel holder as by threading or brazing.

Slip system determination in cubic carbides by hardness anisotropy

Abstract: Hardness has been examined as a function of indenter orientation on the (001) surfaces of the cubic transition-metal carbides titanium carbide, vanadium carbide, zirconium carbide and niobium carbide. To emphasize the observed anisotropy a Knoop indenter was used. Experiments have been performed in the temperature range -196 to 610$^{\circ}$C. The anisotropy curves obtained at each temperature have been analysed in terms of operative slip systems. Three different temperature regimes for the anistropy have been identified. These correspond to the {110} $\langle 1\overline{1}0\rangle $ slip systems for the low-temperature regime, the {111} $\langle 1\overline{1}0\rangle $ slip system for the high-temperature regime and a combination of these two systems for the intermediate-temperature regime. To explain this change in slip system it is proposed that an important temperature dependent change in bonding occurs. A qualitative model is suggested for this change in which an increased density of high mobility electrons increasingly screens the directional covalent bonds as the temperature is raised.

Vibration damping coatings

Abstract: Nickel, cobalt, aluminum, iron-nickel, molybdenum, and titanium alloy articles are provided with a plasma sprayed coating for increasing the vibration damping capacity thereof. The coating consists of a outermost layer portion formed of an oxide ceramic or refractory carbide and an intermediate portion formed of a mixture of one of the above alloys and the material forming the outermost layer. In the preferred embodiment, the intermediate portion consists of two or more discrete layers, with the layers having decreasing alloy content and increasing oxide ceramic content toward the outermost layer portion.

Microstructural development during the liquid-phase sintering of VC-Co alloys

Abstract: A study was made of the microstructural changes that occur during the liquid-phase sintering of VC-Co alloys. It was found that considerable growth of the carbide grains takes place and that this growth can be described by the equation: $$\bar d^3 - \bar d_o^3 = Kt$$

Growth mechanism of polycrystalline β‐SiC layers on silicon substrate

Abstract: The surface of monocrystalline silicon was chemically converted with hydrocarbon to polycrystalline β‐silicon carbide, and the growth mechanism was investigated by means of 14C tracer method. It is shown that the growth of the silicon carbide layer is due to diffusion of silicon through the SiC layer so that the Si–SiC conversion is taking place at the surface of the sample. Dependence of layer thickness on carbidizing time and on hydrocarbon concentration in the carrier gas hydrogen was measured.

Investigation of carbide phase in strained steel by the method of nuclear gamma resonance

Abstract: The Mossbauer effect was used to investigate the cementite state in cold-worked steel. An intensive dissociation of cementite is found at plastic deformation of the steel with the structure of plate perlite. For deformation of 93% this dissociation amounts to 50%. The effect of dissociation was not observed in the steel with granular perlite. The fact that cementite dissociates at deformation may be explained by the increase of bond energy between C atoms and dislocations as compared to that for carbon in the cementite lattice. Alloying with the elements which decrease the bond of dislocations and substitutional impurities has the result that the cementite becomes much more stable at deformation. This is shown on the example of steel containing cobalt. The latter fact influences strongly the mechanical properties of a cold worked steel. [Russian text ignored].

Hard-facing article

Abstract: A hard facing wear pad usable, for example, by brazing to a digger tooth or the like is provided in practice of this invention. The wear pad is from 70 to 85 percent by volume particles of cemented metal carbide in a metal matrix having a melting point not substantially higher than the melting point of the metal cementing the carbide. The cemented carbide particles are in the size range of from about 6 to 30 U.S. Sieve, and the thickness of the pad is within limits determined by the cemented carbide particle size.

Sintered cemented carbide body coated with two layers

Abstract: A sintered hard metal body (e.g., a cutting insert) is provided as to wear resistance by depositing thereon an intermediate thin coating of a metallic carbide or metallic nitride free from binder metal and applying over this intermediate coating a thin ceramic coating free from binder metal.

Measurement of Fracture Surface Energy of SiC

Abstract: The fracture surface energies of 5 polycrystalline silicon carbides were measured at room temperature using the double-cantilever-beam, notched-beam, and work-of-fracture methods. All methods yielded comparable fracture surface energies,

Thermodynamics and phase relations in refractory metal solid solutions containing carbon, nitrogen, and oxygen

Abstract: The refractory metals Nb, Ta, Mo, and W dissolve C, N, and O by forming interstitial solid solutions The concentration of these components can be increased or decreased by annealing treatments, depending on the partial pressure of gases such as N2, O2, H2O, CH4, or CO and on the temperature of the specimen New results in binary and ternary systems combined with those obtained in the last few years now provide most of the data needed for the thermochemical analysis of the solid solution phases and for the establishment of p-T-c phase diagrams The mechanisms of the gas-metal reactions and the general feature of the constitution diagrams are similar for all refractory metals However, marked differences exist between group Va metals niobium and tantalum and group VIa metals molybdenum and tungsten in the absolute values and temperature dependence of the equilibrium pressure of gaseous species and therefore also in the amount of gas absorbed The data now available for the estimation of the final content of interstitials in solid solution after annealing treatments are compiled and discussed

Dense composite ceramic bodies and method for their production

Abstract: Hard, dense composite ceramic bodies of titanium diboride, boron carbide, silicon carbide and silicon, having a wide variety of utilities, are produced by forming a mixture of titanium diboride, boron carbide and a temporary binder into a desired shape to obtain a coherent green body which is siliconized by heating it in contact with silicon to a temperature above the melting point of silicon, whereupon the molten silicon infiltrates the body and reacts with some of the boron carbide therein to produce silicon carbide in situ.

Atomic and Molecular Diffraction and Scattering from a Tungsten Carbide Surface Characterized by LEED

Abstract: The scattering of collimated beams of helium, deuterium, neon, and argon are reported from two tungsten carbide surfaces which form on the (110) face of tungsten. On a (3× 5) surface both helium and deuterium give sharp, well‐defined diffraction peaks corresponding to the (2, 0), (1, 0), (0, 0), (1, 0), (2, 0) directions along the 5 spacing. No diffraction is observed on the (1× 1) carbide surface or the clean metal surface which is also (1× 1). Fractions scattered in the specular ray, (0, 0), as high as 55% have been observed from the carbide surfaces. The scattering of neon is in the inelastic regime and argon is trapping dominated. Analysis of the scattering in combination with the LEED suggests a dense carbide, perhaps WC, with a Debye temperature of 1200°K or higher. This diffractive scattering is the first reported on a surface other than alkali halides and some comments on the sort of periodic potential which is likely to give rise to diffractive scattering of atoms are given.

Fine structure in quenched Fe-Al-C steels

Abstract: The origin of “extra” spots in electron diffraction patterns taken from retained austenite and martensite in Fe-7 pct Al-2 pct C has been investigated. The present interpretation differs from that of previous investigators. It is concluded that a high density of fine carbide precipitates 50A in diameter is responsible for the extra reflections. The precipitates have the perovskite structure and grow epitaxially in the austenite during quenching. When martensite forms at a lower temperature, the precipitates are transformedin situ.

High rate deposition of carbides by activated reactive evaporation

Abstract: Process and apparatus for the production of carbide films at high rates by physical vapor deposition. The metal is evaporated in a vacuum chamber by an electron beam, the hydrocarbon gas is introduced into the chamber, and the metal vapor atoms and gas atoms are activated by electrons deflected from the electron beam to the reaction zone by a low voltage electrode at the reaction zone. The reaction takes place primarily in the vapor phase in the reaction zone, rather than on the substrate. A high reaction efficiency is obtained with the activated atoms and a deposition rate in the range of 1 to 12 micrometers per minute and higher is achieved.

Carbon fiber reinforced nickel matrix composite having an intermediate layer of metal carbide

Abstract: Composite articles having a nickel base metal matrix reinforced with a plurality of high strength, high modulus carbon fibers having a thin, intermediate layer of a metal carbide disposed upon at least a portion of the fiber surfaces. Such composites are characterized by improved thermal cycling characteristics and are produced by coating a plurality of carbon fibers first with a thin, continuous layer of nickel, and then with a second thin, continuous overcoating of a metal capable of diffusing through the nickel coating and reacting with carbon to form a metal carbide; and then hot pressing the dual-coated fibers for a time and at a temperature and pressure sufficient to bond them together and diffuse at least a portion of the carbide-forming metal surface layer through the nickel undercoating and effect reaction between said carbide-forming metal and said carbon fibers to produce a metal carbide coating on at least a portion of the surface of the fibers.

Treating nickel base alloys

Abstract: A method of treating a nickel base alloy so as to produce an alloy having a structure characterized by dispersed discrete fine spherical carbides. The method comprises the steps of casting an ingot of nickel base alloy, homogenizing the ingot at a temperature of from 2,200* to 2,400* F so as to dissolve primary carbides present in the alloy and increase the chemical homogeneity thereof, cooling the alloy at a rate which substantially precludes the precipitation of coarse and film-like carbides at temperatures above 1,900* F and at a second rate in which dispersed fine spherical carbides precipitate at temperatures below 1,900* F; and hot working the alloy at a temperature lower than that at which the primary carbides dissolve.

Carbide alloys suitable for cutting tools and wear parts

Abstract: This invention relates to refractory metal bonded carbide alloys for use as cutting tools and in other applications where high hardness and abrasion resistance are required. The desired finegrain, lamellar microstructure is obtained preferably by casting eutectic, or near-eutectic composition alloys of a Group IVa metal (titanium, zirconium, hafnium), tungsten and carbon which may contain certain alloying and inert materials. For selected applications, the composites may be fabricated by powdermetallurgical techniques.

Tool alloy compositions and methods of fabrication

Abstract: A composition of material comprising a titanium molybdenum carbide and an iron group metal binder is disclosed which is particularly useful as a metal cutting tool. The carbide phase of the composition is substantially richer in carbon than the prior art. For any given metal exchange ration, the carbide phase contains more carbon than the composition line TiC-Mo2C for the same ratio. Also, the carbide phase can contain higher amounts of molybdenum than was used in the prior art.

The Mechanical Design of TRISO-Coated Particle Fuels for the Large HTGR

Abstract: The performance of TRISO-coated carbide fissile particles, of the type to be used in the large HTGR, correlates well with statistically based calculations of stresses in the SiC coating. Three coat...

STUDIES OF THE BINDER PHASE IN WC-Co CEMENTED CARBIDES HEAT-TREATED AT 650°C*

Abstract: The binder phase of WC-Co cemented carbide is a Co-rich alloy in which tungsten and carbon are in solid solution. The binder phase is supersaturated with respect to tungsten even after slow cooling from the sintering temperature. In this study the binder phase contained 6% W in solid solution before heat-treatment at 650°C (923 K). Transmission electron microscopy on thin foils of binder phase showed that a finely dispersed. phase, α′, precipitated in the cubic binder phase. After long ageing times Co3W could be identified by X-ray diffraction methods. As no discontinuous , ‘cells’ of Co3W and ∊-Co could be observed, the following reaction is suggested.α-Co(W, C)→α-Co+α′→α-Co (C)+Co3W (needles)The precipitation of α′ was accompanied by an increase in hardness and a decrease in transverse rupture strength. The effects observed are consistent with those found during annealing of Co-rich cobalt-tungsten-carbon alloys (> 85% Co).