Showing papers on "Carbide published in 2006"
25 Nov 2006-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, a novel concept for the heat treatment of martensite, different to customary quenching and tempering, is described, which can be used to generate microstructures with martensites/austenite combinations giving attractive properties.
Abstract: A novel concept for the heat treatment of martensite, different to customary quenching and tempering, is described. This involves quenching to below the martensite-start temperature and directly ageing, either at, or above, the initial quench temperature. If competing reactions, principally carbide precipitation, are suppressed by appropriate alloying, the carbon partitions from the supersaturated martensite phase to the untransformed austenite phase, thereby increasing the stability of the residual austenite upon subsequent cooling to room temperature. This novel treatment has been termed ‘quenching and partitioning’ (Q&P), to distinguish it from quenching and tempering, and can be used to generate microstructures with martensite/austenite combinations giving attractive properties. Another approach that has been used to produce austenite-containing microstructures is by alloying to suppress carbide precipitation during the formation of bainitic structures, and interesting comparisons can be made between the two approaches. Moreover, formation of carbide-free bainite during the Q&P partitioning treatment may be a reaction competing for carbon, although this could also be used constructively as an additional stage of Q&P partitioning to form part of the final microstructure. Amongst the ferrous alloys examined so far are medium carbon bar steels and low carbon formable TRIP-assisted sheet steels.
618 citations
TL;DR: In this paper, the interfacial reaction between the Al and the CNTs was investigated by annealing the samples at various temperatures and microscopy observation revealed that the reaction generally occurred at locations containing an amorphous carbon coating, at defect sites, and at open ends of CNT arrays.
415 citations
TL;DR: In this paper, a systematic experimental investigation of a large number of carbide-derived carbons with controlled pore size distributions and specific surface area (SSA) was conducted to investigate the effect of small pore sizes on the heat and volume of adsorbed H2.
Abstract: Cryoadsorption is a promising method of enhancing gravimetric and volumetric onboard H2 storage capacity for future trans- portation needs. Inexpensive carbide-derived carbons (CDCs), produced by chlorination of metal carbides, have up to 80% open-pore volume with tunable pore size and specific surface area (SSA). Tuning the carbon structure and pore size with high sensitivity by using different starting carbides and chlorination temperatures allows rational design of carbon materials with en- hanced C-H2 interaction and thus increased H2 storage capacity. A systematic experimental investigation of a large number of CDCs with controlled pore size distributions and SSAs shows how smaller pores increase both the heat of adsorption and the total volume of adsorbed H2. It has been demonstrated that increasing the average heat of H2 adsorption above 6.6 kJmol -1 substantially enhances H2 uptake at 1 atm (1 atm=101325 Pa) and -196°C. The heats of adsorption up to 11 kJmol -1 exceed values reported for metal-organic framework compounds and carbon nanotubes.
377 citations
TL;DR: In this paper, high surface area nanoporous carbon has been prepared by thermo-chemical etching of titanium carbide TiC in chlorine in the temperature range 200-1200-C. Structural analysis showed that this carbide-derived carbon was highly disordered at all synthesis temperatures.
376 citations
TL;DR: A series of iron-based Fischer-Tropsch catalysts, either pure or promoted with Ce or Mn, were subjected to different activation treatments with H2, CO, or H2/CO as mentioned in this paper.
255 citations
TL;DR: In this paper, metal-matrix composites were produced by reinforcing aluminum and aluminum-silicon with diamond single crystals via two different liquid metal infiltration techniques, gas pressure infiltration and mechanically assisted infiltration (squeeze casting).
224 citations
TL;DR: In this article, the crystal structures of the tungsten monocarbide δ-WC and the disordered lower carbide β-W2C were studied using magnetic susceptibility measurements.
Abstract: The crystal structures of the tungsten monocarbide δ-WC and the disordered lower carbide β-W2C are studied. Using magnetic susceptibility measurements, the hexagonal carbide δ-WC is shown to be stable from 300 to 1200 K. The sequence of phase transformations associated with β-W2C ordering is analyzed. The temperature and composition stability limits of the cubic carbide γ-WC1−x are evaluated, and the first data are presented on the variation of its lattice parameter with composition. An optimized W-C phase diagram is proposed which takes into account detailed structural and phase-equilibrium data for tungsten carbides.
219 citations
TL;DR: In this paper, the authors compared the wear resistance of tungsten carbide and chromium carbide-based coatings with a three-body solid particle rubber wheel test rig using silica grits as the abrasive medium.
Abstract: Thermally sprayed tungsten carbide-based and chromium carbide-based coatings are being widely used for a variety of wear resistance applications. These coatings deposited by high velocity processes like high velocity oxy-fuel (HVOF) and detonation gun spray (DS) techniques are known to provide improved wear performance. In the present study, WC–10Co–4Cr and Cr3C2–20(NiCr) coatings are deposited by HVOF and pulsed DS processes, and low stress abrasion wear resistance of these coatings are compared. The abrasion tests were done using a three-body solid particle rubber wheel test rig using silica grits as the abrasive medium. The results show that the DS coating performs slightly better than the HVOF coating possibly due to the higher residual compressive stresses induced by the former process and WC-based coating has higher wear resistance in comparison to Cr3C2-based coating. Also, the thermally sprayed carbide-based coatings have excellent wear resistance with respect to the hard chrome coatings.
212 citations
TL;DR: Density functional theory was employed to investigate the behavior of Mo carbides in the water-gas-shift reaction and it is shown that the O-covered Mo-terminated Mo(2)C(001) (O_Mo-Mo( 2)C) surface displays the lowest WGS activity of all.
Abstract: Density functional theory (DFT) was employed to investigate the behavior of Mo carbides in the water-gas-shift reaction (WGS, CO + H2O → H2 +CO2). The kinetics of the WGS reaction was studied on the surfaces of Mo-terminated Mo2C(001) (Mo−Mo2C), C-terminated Mo2C(001) (C−Mo2C), and Cu(111) as a known active catalyst. Our results show that the WGS activity decreases in a sequence: Cu > C−Mo2C > Mo−Mo2C. The slow kinetics on C−Mo2C and Mo−Mo2C is due to the fact that the C or Mo sites bond oxygen too strongly to allow the facile removal of this species. In fact, due to the strong O−Mo and O−C interactions, the carbide surfaces are likely to be covered by O produced from the H2O dissociation. It is shown that the O-covered Mo-terminated Mo2C(001) (O_Mo−Mo2C) surface displays the lowest WGS activity of all. With the Mo oxide in the surface, O_Mo−Mo2C is too inert to adsorb CO or to dissociate H2O. In contrast, the same amount of O on the C−Mo2C surface (O_C−Mo2C) does not lead to deactivation, but enhances t...
198 citations
Patent•
01 Nov 2006TL;DR: In this paper, metal carbide thin films are formed in an atomic layer deposition (ALD) process by alternately and sequentially contacting a substrate in a reaction space with spatially and temporally separated vapor phase pulses of a metal source chemical, a reducing agent and a carbon source chemical.
Abstract: Methods of forming metal carbide thin films are provided. According to preferred embodiments, metal carbide thin films are formed in an atomic layer deposition (ALD) process by alternately and sequentially contacting a substrate in a reaction space with spatially and temporally separated vapor phase pulses of a metal source chemical, a reducing agent and a carbon source chemical. The reducing agent is preferably selected from the group consisting of excited species of hydrogen and silicon-containing compounds.
187 citations
TL;DR: In this paper, the effects of Co content and WC grain size on wear were examined for 13 different carbide types and showed that wear increased with both co content and grain size of the carbide.
TL;DR: In this article, low-temperature gas-phase carburization has been used to generate very high surface interstitial carbon contents, up to ∼12 at.%, in a 316L austenitic stainless steel.
Patent•
31 Mar 2006TL;DR: In this article, a method for forming a metal carbide or metal carbonitride film on a substrate using a vapor deposition process is described, which includes introducing a first process material such as a film precursor, to the substrate followed by introducing a second process material, such as the film reducing agent.
Abstract: A method for forming a metal carbide or metal carbonitride film on a substrate using a vapor deposition process. The method includes comprises introducing a first process material, such as a film precursor, to the substrate followed by introducing a second process material, such as a film reducing agent, to the substrate, whereby plasma can be formed during the introduction of the second process material in order to assist reduction of the first process material on the substrate. Additionally, the temperature of the substrate is elevated to a value approximately equal to or greater than the decomposition temperature of the first process material in order to improve adhesion properties for the metal carbide or metal carbonitride film.
TL;DR: In this paper, a study on the performance of alloyed carbide tools during dry machining of the titanium alloy Ti-6242S, commonly used for aeroengines, is presented.
Abstract: This paper deals with a study on the performance of alloyed carbide tools during dry machining of the titanium alloy Ti-6242S, commonly used for aeroengines. Experimental tests were conducted using two kinds of alloyed carbide tool inserts: the uncoated carbide tool (tool A) and the multi-layer CVD-coated tool (tool B). Tool failure modes and wear mechanisms for both tools were examined at various cutting conditions. The localized flank wear (VB) was found to be the predominant tool wear for both tools A and B. At VB close to 0.3 mm, a brittle fracture (cracking, flaking and chipping) was noted, a plastic deformation was significantly observed and a phenomenon of coating delamination was noticed. Adhesion wear (attrition and galling) and diffusion wear have been the wear mechanisms of tools A and B. Coating delamination was the initial wear mode of tool B; it occurred after a few seconds of cutting time. The performance of the uncoated and the multi-layer CVD-coated alloyed carbide tools was analyzed in terms of tool life and surface finish. Thanks to the Finite Element Analysis (FEA) on the tribological parameters and on the chip segmentation, a new proposal on the physical mechanisms of coating delamination was carried out.
Patent•
22 Jun 2006TL;DR: In this paper, an epitaxial silicon carbide layer is fabricated by forming first features in a surface of a substrate having an off-axis orientation toward a crystallographic direction.
Abstract: An epitaxial silicon carbide layer is fabricated by forming first features in a surface of a silicon carbide substrate having an off-axis orientation toward a crystallographic direction. The first features include at least one sidewall that is orientated nonparallel (i.e., oblique or perpendicular) to the crystallographic direction. A first epitaxial silicon carbide layer is then grown on the surface of the silicon carbide substrate that includes first features therein. Second features are then formed in the first epitaxial layer. The second features include at least one sidewall that is oriented nonparallel to the crystallographic direction. A second epitaxial silicon carbide layer is then grown on the surface of the first epitaxial silicon carbide layer that includes the second features therein.
05 May 2006
TL;DR: In this article, the feasibility of employing a reactive ion etching process (RIE) with chlorine gas at low temperature, as opposed to the current high temperature chlorination process, in achieving the conversion of metal carbide films into amorphous carbon films was examined.
Abstract: The excellent tribological properties, very low friction coefficient, ~0.05, of the recently discovered carbide derived carbon (CDC) films have shown them to be excellent candidates in many applications where friction and wear are dominating issues in performance. In this work we examine the feasibility of employing a reactive ion etching process (RIE) with chlorine gas at low temperature, as opposed to the current high temperature chlorination process, in achieving the conversion of metal carbide films into amorphous carbon films. The overall goal is develop a process that is friendlier to microfabricated devices towards employing the tribological properties of CDC films in such devices. We examine this RIE processing using both bulk scale and thin film specimens. These metal-carbide specimens are subjected to a halogen containing ion plasma at reduced pressure in order to leach out the metal, resulting in an amorphous carbon film, a so-called carbide-derived carbon (CDC) process. This reactive ion etching process has been used to produce carbon layers on multiphase carbide materials containing silicon and titanium. The resulting carbon layers have been characterized using a variety of techniques. The results on the bulk scale specimens, via Raman spectrometry, indicated that RIE processing can indeed achieve conversion, while results of the thin films indicated that although conversion occurred poor adhesion of the films to the substrate resulted spallation during friction testing attempts.
TL;DR: In this article, the results of experimental and theoretical investigations of phase equilibria in the W-C system and of the crystal and electronic structures of tungsten carbides are generalised.
Abstract: The results of experimental and theoretical investigations of phase equilibria in the W–C system and of the crystal and electronic structures of tungsten carbides are generalised. The phase diagram of the W–C system supplemented by new compounds is considered. The sequence of phase transformations associated with ordering of lower hexagonal carbide β-W2C is analysed. The region of existence of cubic carbide γ-WC1–x is discussed in detail. The generalised information on the phase equilibria in the ternary system W–Co–C, which forms the basis for the synthesis of hard alloys WC–Co, is given. Methods of synthesis of tungsten carbides and hard alloys based on them are considered. Modern methods for the synthesis of nanostructured hard alloys are discussed in detail as well as their structures and properties.
TL;DR: In this article, the authors investigated the mechanism of surface modification associated with the high-current pulsed electron beam (HCPEB) treatment of a D2 steel with increasing numbers of pulses.
TL;DR: In this paper, the microstructure of high velocity oxy-fuel (HVOF) sprayed Cr 3 C 2 -NiCr coatings was characterized by scanning electron microscopy, and the apparent average size and volume fraction of carbide particles in the coatings were estimated through quantitative imaging analysis.
Abstract: Cr 3 C 2 –NiCr coatings were deposited by high velocity oxy-fuel (HVOF) process with different spray parameters to examine dominant microstructural factors in abrasive wear of the coatings. The microstructure of the HVOF sprayed Cr 3 C 2 –NiCr coatings was characterized by scanning electron microscopy and transmission electron microscopy (TEM). The apparent average size and volume fraction of carbide particles in the coatings were estimated through a quantitative imaging analysis. The formation of carbide phases in the coating was discussed based on the TEM observation results. The abrasive wear behavior of the coating was evaluated by the dry rubber wheel abrasive wear test and the wear mechanisms were elucidated. Influences of apparent size and volume fraction of carbide particles on the abrasive wear weight loss were examined through correlating the proposed relation with the experimental results. Results showed that Cr 3 C 2 particle size was significantly reduced after the spraying and Cr 7 C 3 carbide was present around Cr 3 C 2 particles, and Cr 23 C 6 carbide was dispersed in NiCr alloy matrix with a nano-crystalline structure. The three carbides were formed in the coating through different mechanisms. The removal of carbide particles in the coating was mainly responsible for the abrasive wear of the coating. The content and particle size of the Cr 3 C 2 carbides were the two key factors controlling the abrasive wear of the HVOF sprayed Cr 3 C 2 –NiCr coatings.
TL;DR: In this paper, the combined effect of pretreatments and substrate microstructure on the adhesive toughness and wear rate of CVD diamond in dry machining of highly abrasive materials was analyzed.
TL;DR: In this article, the reactive hot pressing (RHP) was used to produce Zirconium diboride-silicon carbide ceramics with relative densities in excess of 95% at temperatures as low as 1650°C.
Abstract: Zirconium diboride–silicon carbide ceramics with relative densities in excess of 95% were produced by reactive hot pressing (RHP) at temperatures as low as 1650°C. The ZrB2 matrix was formed by reacting elemental zirconium and boron. Attrition milling of the starting powders produced nanosized (<100 nm) Zr particulates that reacted with B below 600°C. The reaction resulted in the formation of nanoscale ZrB2 crystallites that could be densified more than 250°C below the temperatures required for conventional ZrB2 powder. Because of the low-temperature densification, the resulting ZrB2 grain sizes were as small as 0.5±0.30 μm for specimens densified at 1650°C and 1.5±1.2 μm for specimens densified at 1800°C. Vickers hardness, elastic modulus, and flexure strength of fully dense materials produced by RHP were 27, 510, and 800 MPa, respectively.
TL;DR: In this article, the electronic structure and formation energies of cementite-like carbides and borides of Groups VII-VIII transition metals (TMs) (M3X) were investigated.
Abstract: Density functional theory within the generalized gradient approximation (GGA) is used to investigate the electronic structure and formation energies of cementite-like carbides and borides of Groups VII–VIII transition metals (TMs) (M3X; where M=Fe, Co, Ni; X=C or B). All phases are metallic-like; Fe3C, Co3C, Fe3B and Co3B exhibit ferromagnetic states whereas Ni3C and Ni3B are paramagnetic. The formation energies of M3X calculated with respect to bulk TMs, graphite and α-boron (B12) are negative for borides, however, they are positive for carbides, i.e. these M3C phases are metastable or unstable at ambient conditions. The stability differences of these compounds are discussed in terms of their electronic structure and chemical bonding.
TL;DR: In this article, the water-gas shift (WGS) reaction over a series of cobalt-molybdenum carbide catalysts was studied at 453 K. The catalysts were characterized using X-ray diffraction, CO adsorption, temperature-programmed carburization (TPC) with a 20% CH 4 /H 2 mixture.
TL;DR: In this article, the friction and wear behavior of cermets/steel rubbing pairs were investigated. Friction and wear tests were carried out using three different cremets on the base of tungsten, titanium and chromium carbides under dry sliding conditions against steel disk (0.45% C).
TL;DR: In this article, low and high-temperature Raman spectroscopy of pressure-induced amorphous boron carbide (a-B4C) was performed and it was shown that the amorphization of B4C is associated with the destruction of the C-B-C chains.
Abstract: We report low- and high-temperature Raman spectroscopy of pressure-induced amorphous boron carbide (a-B4C). Coarsening of carbon clusters in a-B4C was characterized during heating, whereas unusual temperature coefficients of a-B4C Raman peak shifts were observed during cooling. These results experimentally evidence that the amorphization of B4C is associated with the destruction of the C–B–C chains and a-B4C is composed of sp2 carbon aromatic rings and boron clusters. This disordered structure with relatively weak carbon sp2 bonds is believed to be responsible for the loss of B4C shear strength at high pressures.
TL;DR: Theoretical lattice parameters and bulk modulus of TaCx slabs and Al atomic planes in ternary Ta-Al-C carbides were analyzed in this article.
Abstract: Direct atomic resolution observations of the layered stacking characteristics of TaCx slabs and Al atomic planes in ternary Ta-Al-C carbides were achieved. Layered ternary Ta-Al-C compounds have diverse structures. A previously unknown Ta6AlC5 carbide, as well as intergrown Ta2AlC-Ta4AlC3 and Ta4AlC3-Ta6AlC5 structures were identified. Theoretical lattice parameters and bulk modulus of Ta2AlC, Ta3AlC2, Ta4AlC3, and Ta6AlC5 are presented. Furthermore, the Ta-C bonds are much stronger than the Ta-Al bonds in ternary Ta-Al-C carbides, which accounts for the enhancement of bulk modulus with increasing Ta-C layers.
TL;DR: In this article, the influence of the type of particle both on the codeposition process and on the coating properties was analyzed by incorporating two kinds of particles, SiC and Si3N4.
Abstract: Electroless NiP composite coatings were obtained by incorporating two kinds of particles, SiC and Si3N4, to analyze the influence of the type of particle both on the codeposition process and on the coating properties. Particles with sizes ranging from 30 nm to 2 μm were selected to study the influence of this parameter on the amount of embedded particles. All composite coatings were characterized by composition, morphology, structure, roughness and some tribological properties. Results indicated that, while there was almost no difference between carbide and nitride incorporation for micron-sized particles, this variable was very important with the nano-sized ones. Moreover, it was observed that the growth mechanism of the metallic matrix was much more modified by the nano-particles than by the micron-sized ones.
TL;DR: In this paper, the suitability of uncoated cemented carbide tools in ball-end milling of the aerospace titanium alloy Ti-6242S was investigated under dry cutting condition.
Abstract: Titanium alloy is widely used in the aerospace industry for applications requiring high strength at elevated temperature and high mechanical resistance. The difficulty of dislocation motion through the microstructure is responsible for its high yield strength. However, the main problems encountered when machining titanium alloy are the low material removal rate and the short tool life. This study investigated the suitability of uncoated cemented carbide tools in ball-end milling of the aerospace titanium alloy Ti-6242S. The experiments were carried out under dry cutting condition. Cutting speeds in the range of 60–150 m/min were considered. The axial and radial depths of cut were kept constant at 2.0 and 8.8 mm, respectively, and the feed rate values of 0.1 and 0.15 mm/tooth were selected. SEM analysis has been carried out on the worn tools and shows that flank wear and excessive chipping on the flank edge are the main tool failure modes. For both feed rates, the results demonstrate that the higher the cutting speed the better is the surface finish. The FEM simulation provides good results on modelling of chip formation and can be helpful to calculate the contact parameters and to understand the tool wear mechanisms when dry machining aerospace titanium alloys.
TL;DR: Results indicate that nanodimensional Cr crystallites formed during the electrodeposition process are characterized by very high electrocatalytic activity.
Abstract: Valence-to-core X-ray emission spectroscopy was applied to study a composition of chromium coatings electrodeposited from Cr(III) sulfate electrolytes with the addition of formic or oxalic acid. It was shown that the obtained crystallographically amorphous deposits contain chromium carbide compounds. These results indicate that nanodimensional Cr crystallites formed during the electrodeposition process are characterized by very high electrocatalytic activity.