Showing papers on "Carbide published in 2002"

Solid–liquid reaction synthesis of layered machinable Ti3AlC2 ceramic

Abstract: Fully dense polycrystalline Ti3AlC2 was fabricated by a solid–liquid reaction synthesis and simultaneous in-situ hot pressing of a mixture of Ti, Al and graphite powders at 1500 °C and 25 MPa for 5 minutes and subsequently annealing at 1200 °C for 20 minutes. The effects of various parameters including composition of the initial elemental powders, temperature as well as the hot pressing pressure on the purity, formation and densification of Ti3AlC2 were examined. In addition, the reaction path for the formation of Ti3AlC2 was investigated by DTA, XRD, SEM and EDS, suggesting that the reaction path during the heating process could be reasonably described as follows: Al powder melted at some 660 °C and coated the Ti particles; at about 740 °C the exothermic reactions between Al and Ti occurred and Ti–Al intermetallics like TiAl and Ti3Al were formed; the diffusion of carbon in the Ti–Al intermetallics at elevated temperature resulted in the carbides Ti2AlC, Ti3AlC and TiC; and finally these carbides and the unreacted graphite reacted at about 1420 °C to yield Ti3AlC2.

Direct Selective Laser Sintering of Hard Metal Powders: Experimental Study and Simulation

Abstract: Direct selective laser sintering (SLS) technology can be used to produce 3D hard metal functional parts from commercial available powders. Unlike conventional sintering, it does not require dedicated tools, such as dies. Hence, total production time and cost can be reduced. The large shape freedom offered by such a process makes the use of, for example, sintered carbides components viable in domains where they were not applied before. Successful results have been obtained in the production of sintered carbide or hard metal parts through SLS. The investigation focuses on tungsten carbide-cobalt (WC-Co) powder mixture. This material is characterised by its high mechanical properties and its high wear resistance and is widely used in the field of cutting tools. This paper is devoted to the experimental study and the simulation of direct selective laser sintering of WC-Co hard metal powders.

Metal nitride deposition by ALD with reduction pulse

Abstract: The present methods provide tools for growing conformal metal thin films, including metal nitride, metal carbide and metal nitride carbide thin films. In particular, methods are provided for growing such films from aggressive chemicals. The amount of corrosive chemical compounds, such as hydrogen halides, is reduced during the deposition of transition metal, transition metal carbide, transition metal nitride and transition metal nitride carbide thin films on various surfaces, such as metals and oxides. Getter compounds protect surfaces sensitive to hydrogen halides and ammonium halides, such as aluminum, copper, silicon oxide and the layers being deposited, against corrosion. Nanolaminate structures incorporating metallic thin films, and methods for forming the same, are also disclosed.

Study on the Structure and Formation Mechanism of Molybdenum Carbides

Abstract: The synthesis of high-surface-area molybdenum carbides has been studied by the temperature-programmed carburization of molybdenum trioxide MoO3. The feedstocks used were mixtures of methane and ethane with hydrogen. The solid reaction products were characterized at selected intervals using thermogravimetric analysis differential scanning calorimetry (TGA-DSC), surface area measurement (BET), X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HRTEM). The gaseous products of the carburization process were monitored using a gas chromatograph equipped with a mass spectrometer (GC-MS). The structural properties of the product carbides are shown to depend on the conditions of synthesis. The C2H6/H2 feedstock gave the highest-surface-area material. The presence of H2 in the feed mixture reduced the amount of amorphous carbon deposited an the molybdenum carbide material. The surface area was found to increase most rapidly during the initial H2-reduction stage. Initially, the MoO3 is re...

Plasma spray deposition and high temperature characterization of ZrB2–SiC protective coatings

Abstract: Refractory metal borides are the object of special interest for aerospace applications requiring properties of chemical and mechanical resistance in ultra high temperature, such as nose and leading edges of re-entry space vehicles. The main objective of the research is the fabrication and characterization of plasma sprayed zirconium diboride–silicon carbide composite coatings and free-standing components for high temperature applications. High and low pressure plasma spray in a controlled atmosphere were selected as manufacturing techniques for the deposition of ceramic coatings. Fine ZrB2 and SiC precursors were agglomerated and preconsolidated into spherical, hollow powders for better flowability and silicon carbide thermal protection during the interaction with the plasma. Coatings and free-standing tubular specimens were fabricated and tested for high temperature behaviour. Thermogravimetric analysis, surface morphology investigation and high temperature X-ray diffraction showed that the addition of approximately 25% SiC induces a mechanism of self-protection of the ceramic material during heat treatment in oxidizing environments up to approximately 2100 K.

Structural Relaxation of Amorphous Silicon Carbide

Abstract: We have examined amorphous structures of silicon carbide (SiC) using both transmission electron microscopy and a molecular-dynamics approach. Radial distribution functions revealed that amorphous SiC contains not only heteronuclear (Si-C) bonds but also homonuclear (Si-Si and C-C) bonds. The ratio of heteronuclear to homonuclear bonds was found to change upon annealing, suggesting that structural relaxation of the amorphous SiC occurred. Good agreement was obtained between the simulated and experimentally measured radial distribution functions.

Rapid synthesis of ternary carbide Ti3SiC2 through pulse-discharge sintering technique from Ti/Si/TiC powders

Abstract: Ti/Si/TiC powders with molar ratios of 1:1:2 (M1) and 2:2:3 (M2) were prepared for the synthesis of a ternary carbide Ti3SiC2 by using the mixture method for 24 hours in an Ar atmosphere. The synthesis process was conducted at 1200 °C to 1400 °C under a pressure of 50 MPa, using the pulse-discharge sintering (PDS) technique. After sintering, the phase constituents and microstructures of the samples were analyzed by X-ray diffraction (XRD) technique and observed by optical microscopy and scanning electron microscopy. The results showed that the phases in all the samples consisted of Ti3SiC2 and small amounts of TiC, and the optimum sintering temperature was found to be in the relatively low range of 1250 °C to 1300 °C. By the standard additive method, the relative content of Ti3SiC2 was calculated. For the M1 samples, the lowest TiC content can be only decreased to about 3 to 4 wt pct, whereas the content of Ti3SiC2 in the M2 samples is always lower than that in the M1 samples. When the M2 powder was sintered at 1300 °C for 8 to 240 minutes, the TiC peaks were found to show a very low intensity, and the corresponding content of Ti3SiC2 was calculated to be higher than 99 wt pct. The grain size of Ti3SiC2 increased from 5 to 10 µm to 80 to 100 µm in the entire applied sintering temperature range. The relative density of the M2 samples was measured to be higher than 99 pct at sintering temperatures above 1275 °C. It indicates that the PDS technique can rapidly synthesize high-content Ti3SiC2 from the Ti/Si/TiC powders in a relatively low temperature range.

The effect of ageing upon the microstructure and mechanical properties of type 15-5 PH stainless steel

Abstract: Microstructures developed in commercial 15-5 PH precipitation-hardened stainless steel after different heat treatments have been studied. In the as received condition, two types of carbides, NbC and M 7 C 3 , were present. Age hardening involves initial formation of fine precipitates rich in copper. Conventional transmission electron microscopy (TEM) and high resolution electron microscopy (HREM) studies have revealed the formation of a 9R structure copper precipitates (4 nm) in the samples aged at temperatures below 500 °C. However, at higher temperatures, in addition to the formation of these precipitates, the austenite phase was formed. After ageing at 500 °C for 128 h, M 23 C 6 carbides were observed. The majority of the M 23 C 6 carbides were in the interface of martensitic matrix and retained austenite. A second type of copper precipitate being, spherical in shape, were observed on ageing at 650 °C. TEM and X-ray microanalysis on thin foils and on carbon extraction replicas used for analysing the structure and metallic compounds of these precipitates. The mechanical properties following strain deformation has been carried out using scanning electron microscope (SEM), TEM and HREM. At peak aged, the 15-5 PH alloy exhibit brittle failure, the major fracture mode was cleavage and/or quasicleavage.

Carbide precipitation and high-temperature strength of hot-rolled high-strength, low-alloy steels containing Nb and Mo

Abstract: The effects of a Mo addition on both the precipitation kinetics and high-temperature strength of a Nb carbide have been investigated in the hot-rolled high-strength, low-alloy (HSLA) steels containing both Nb and Mo. These steels were fabricated by four-pass hot rolling and coiling at 650°C, 600°C, and 550°C. Microstructural analysis of the carbides has been performed using field-emission gun transmission electron microscopy (TEM) employing energy-dispersive X-ray spectroscopy (EDS). The steels containing both Nb and Mo exhibited a higher strength at high temperatures (∼600 °C) in comparison to the steel containing only Nb. The addition of Mo increased the hardenability and led to the refinement of the bainitic microstructure. The proportion of the bainitic phase increased with the increase of Mo content. The TEM observations revealed that the steels containing both Nb and Mo exhibited fine (<10 nm) and uniformly distributed metal carbide (MC)-type carbides, while the carbides were coarse and sparsely distributed in the steels containing Nb only. The EDS analysis also indicated that the fine MC carbides contain both Nb and Mo, and the ratio of Mo/Nb was higher in the finer carbides. In addition, electron diffraction analysis revealed that most of the MC carbides had one variant of the B-N relationship ((100)MC//(100)ferrite, [011]MC//[010]ferrite) with the matrix, suggesting that they were formed in the ferrite region. That is, the addition of Mo increased the nucleation sites of MC carbides in addition to the bainitic transformation, which resulted in finer and denser MC carbides. It is, thus, believed that the enhanced high-temperature strength of the steels containing both Nb and Mo was attributed to both bainitic transformation hardening and the precipitation hardening caused by uniform distribution of fine MC particles.

The influence of nickel coating on the wettability of aluminum on ceramics

Abstract: The wetting behavior and interfacial phenomena of plain and nickel-coated alumina and silicon carbide ceramics with liquid aluminum at 800 °C was investigated. The coatings applied to the ceramic plates improved wettability with aluminum resulting from the dissolution of the coating in the liquid drop. The non-wetting condition of the as received ceramics was overcome to contact angles of 12.2° for Ni-coated SiC and 11.6° for Ni-coated Al2O3. With the addition of nickel as a coating, there was no dissolution of SiC in the alloy, and interfacial carbide did not appear.

Pick for disintegrating natural and man-made materials

Abstract: An attack tool for working natural and man-made materials that is made up of one or more segments, including a steel alloy base segment, an intermediate carbide wear protector segment, and a penetrator segment comprising a carbide substrate that is coated with a superhard material. The segments are joined at continuously curved interfacial surfaces that may be interrupted by grooves, ridges, protrusions, and posts. At least a portion of the curved surfaces vary from one another at about their apex in order to accommodate ease of manufacturing and to concentrate the bonding material in the region of greatest variance. The carbide used for the penetrator and the wear protector may have a cobalt binder, or it may be binderless. It may also be produced by the rapid omnidirectional compaction method as a means of controlling grain growth of the fine cobalt particles. The parts are brazed together in such a manner that the grain size of the carbide is not substantially altered. The superhard coating may consist of diamond, polycrystalline diamond, cubic boron nitride, binderless carbide, or combinations thereof.

Diamond tip point-attack bit

Abstract: A rotatable point-attack bit retained for rotation in a block bore, and used for impacting, fragmenting and removing material from a mine wall. An improved elongated tool body having at the front end a diamond-coated tungsten carbide wear tip that is rotationally symmetric about its longitudinal axis and contiguous with a second section steel shank at the rear end. The two distinct parts are joined by a high impact resistant braze at ratios that prevent tool breakage. The method of making such a diamond-coated section comprises of 1) placing within a reaction cell, the diamond powder and the carbide substrate and 2) simultaneously subjecting the cell and the contents thereof to temperature and pressure at which the diamond particles are stable and form a uniform polycrystalline diamond surface on the tip of the carbide substrate thus forming a diamond-coated insert providing both cutting edge and steel body protection for increased durability and extended cutting tool life.

The metathesis-facilitated synthesis of terminal ruthenium carbide complexes: a unique carbon atom transfer reaction.

Abstract: Ruthenium benzylidene metathesis catalysts react with 2,3-dicarbomethoxymethylene−cyclopropane, eliminating styrene and dimethyl fumarate, and producing the first terminal ruthenium carbide complexes. The products are diamagnetic, air-stable, and moderately soluble in hydrocarbon solvents. An X-ray study of Ru(⋮C:)Cl2(P(C6H11)3) (1,3-dimesityl-4,5-dihydroimidazol-2-ylidene) shows a Ru−C distance of 1.650(2) A, consistent with the presence of a very short Ru−C triple bond.

Examination of the wear properties of HVOF sprayed nanostructured and conventional WC-Co cermets with different binder phase contents

Abstract: There has been an increase in interest of late regarding the properties of thermally sprayed WC-Co cermets with nanograin carbide particles. These powders have shown interesting properties in sintered components, giving high values of hardness (2200–2300 VHN) and improved wear properties. The method used for the processing for these materials—solution formation, spray drying and chemical conversion, rather than introduction of WC as solid particles to a molten binder—allows the formation of sub-100 nm WC particles as a hard second phase.

In Situ TEM Studies of Metal–Carbon Reactions

Abstract: The reactions which occur between amorphous carbon and a number of first transition metals (Ti, Cr, Fe, Co, Ni, and Cu) have been studied by transmission electron microscopy (TEM). The materials are in thin-film form with the metal layer sandwiched between thicker carbon layers. In four cases, the predominant reaction is the graphitization of the amorphous carbon, at temperatures well below 800 degrees C. This is brought about by the elements themselves in the case of Co and Ni, and by metastable carbides in the case of Fe (Fe3C) and Cr (Cr3C2-x). The Ti-C and Cu-C systems do not exhibit graphitization. For the former, only TiC is produced up to 1000 degrees C, while the carbon does not react at all with copper. In situ TEM studies show the mechanism to be of the dissolution-precipitation type, which is equivalent to the metal-mediated crystallization process for amorphous silicon and germanium. The heat of graphitization is found to be 18-19 kcal/mol-C by differential scanning calorimetry.