Titanium Carbide Grains Research Articles

Facile fabrication and characterization of multi-type carbon-doped TiO2 for visible light-activated photocatalytic mineralization of gaseous toluene

Carbon-doped titanium dioxide (C-TiO2) nanoparticles were synthesized by conventional mild oxidation of precursor titanium carbide (TiC) at 350 °C for 2 to 50 hours and more aggressive oxidation at the higher temperature of 400 to 600 °C for 2 hours in air. XRD and TEM studies indicated the formation of nano-sized C-TiO2 with mixed anatase–rutile phases. With prolonged oxidation time or increase in oxidation temperature, an initial decrease in crystallite size was unveiled due to cracking of TiC grains, renucleation of TiO2 and diffusion of carbon atoms. Raman, FTIR and XPS measurements revealed the presence of graphite-like carbon and the coexistence of substitutional and interstitial carbon in the TiO2 lattice. This multi-type carbon doping either served as a photosensitizer or resulted in additional electronic states above the valence band of the TiO2 lattice, directly responsible for the red shift of the absorption edge in the UV-vis absorption spectrum. The band structure and possible visible light photocatalytic mechanism of the C-TiO2 were thus elucidated. The synthesized C-TiO2 nanoparticles demonstrated improved photocatalytic performance for the mineralization of gaseous toluene in comparison to commercial P25 TiO2 under visible light irradiation. The C-TiO2 nanoparticles prepared at higher oxidation temperature with shorter time exhibited a more pronounced enhancement than those prepared by the mild oxidation process, providing a facile method for large-scale production of C-TiO2 suitable for indoor photocatalytic applications.

Study of composite spark-alloyed coatings based on titanium carbide using self-propagating high-temperature synthesis

This work discusses composite coatings obtained by electro-spark alloying and self-propagating high-temperature synthesis. It has been established that the generated composite coatings consist of titanium carbides, which are uniformly distributed in the metal matrix. The titanium carbide grain sizes are in the range of 0.1–4.0 μm. The coarse grains of titanium carbide in the coating consist of disperse carbides with sizes of less than 1 μm. The study of the structure of the composite coatings in friction tracks has demonstrated that the generated coatings possess high wear resistance.

Spherical indentation damage in TiC–Ni 3Al composites

Advanced cermets based on titanium carbide (TiC), with a ductile nickel aluminide (Ni 3Al) binder, have shown significant promise for use in a variety of demanding wear environments, due to a combination of high strength and good corrosion behaviour. In the present study, TiC–Ni 3Al composites were produced by melt infiltration, using aqueous slip cast TiC preforms, and Ni 3Al binder contents from 10 to 50 vol. %. These samples were subjected to spherical indentation testing, with applied loads from 250 to 2000 N, using WC–Co spheres ranging in diameter from 1.19 to 2.38 mm. Indentation stress-strain curves were determined and compared to the calculated elastic (i.e. Hertzian) response. The bonded interface method was used to examine the subsurface damage of the cermets after indentation. Significant deformation of the binder and the eventual fracture of TiC grains were observed. The nature of the quasi-plasticity of TiC–Ni 3Al, and the affect of binder content on surface and subsurface deformation, are discussed.

The effect of carbon content on the microstructure of hydrogen-free physical vapour deposited titanium carbide films

Titanium carbide (TiC) coatings for tribological applications were deposited on high speed steel. Several coatings with different titanium to carbon ratio were deposited by means of physical vapour deposition in which titanium was evaporated and carbon was sputtered. The coatings were characterised using analytical electron microscopy. It was observed that the change in titanium to carbon ratio significantly changed the microstructure of the coatings. The low carbon containing coatings consisted of columnar grains exhibiting a preferred crystallographic orientation whereas the coating with highest carbon content consisted of randomly ordered TiC grains in an amorphous carbon matrix. Energy filtered transmission electron microscopy revealed a change in Ti/C ratio as the distance from the substrate increased. The titanium to carbon ratio was observed to increase with distance from the substrate until a stable level was reached. This is due to a variation in the titanium evaporation during the early stages of film growth. This change of the titanium to carbon ratio affected the columnar growth in the initial stage of coating growth for the coatings with low carbon content.

Growth of TiC octahedron obtained by self-propagating reaction

A large amount of titanium carbide (TiC) octahedra were synthesized in situ by self-propagating high-temperature synthesis using Al, Ti, C elemental powders as source materials. The phase constituents and microstructure morphologies of as-product were characterized by X-ray powder diffraction, field emission scanning electron microscopy and transmission electron microscopy. Due to the strong faceting tendency of the growing TiC crystal, the TiC grain grew as an octahedral morphology. If V [1 0 0] / V [1 1 1] =1.5, the TiC grain will grow as a perfect octahedral morphology. While if V [1 0 0] / V [1 1 1] >1.5, the TiC grain will grow as an imperfect octahedral morphology. According to the experimental results, the detailed microstructure and growth mechanism of TiC octahedron have been observed and analyzed. The models have been proposed to understand the formation and growth mode of TiC octahedron.

Size distribution of titanium-carbide grains in the liquid-phase sintering of Ni-TiC composite

Size distribution of titanium-carbide grains in the liquid-phase sintering of Ni-TiC composite

Crystal growth of TiC grains during SHS reactions

The microstructure formation of TiC during self-propagating high-temperature synthesis (SHS) reactions is investigated thanks to the quenching method. The morphology and chemical composition of titanium carbide grains are characterized, during the growth phase, from X-ray diffraction (XRD), scanning electron microscopy (SEM) and wavelength dispersion spectroscopy (WDS) analyses. It is demonstrated that TiC x grains nucleate with a great deficit in carbon; the carbon composition evolves towards the stoichiometry during the growth phase. The TiC grain sizes are then coupled to thermal data acquired by infra red (IR) thermography. It is shown that the convolution of the temperature and of the time elapsed in the temperature range T max−1000 K constitute a pertinent parameter to give account of the variation of TiC grain sizes.

Constraints on Grain Formation around Carbon Stars from Laboratory Studies of Presolar Graphite

We report the results of an investigation into the physical conditions in the mass outflows of asymptotic giant branch (AGB) carbon stars that are required for the formation of micron-sized presolar graphite grains, with and without previously formed internal crystals of titanium carbide (TiC). A lower mass limit of 1.1 M☉ for stars capable of contributing grains to the solar nebula is derived. This mass limit, in conjunction with a mass-luminosity relation for carbon stars, identifies the region of the H-R diagram relevant to the production of presolar graphite. Detailed dynamical models of AGB outflows, along with constraints provided by kinetics and equilibrium thermodynamics, indicate that grain formation occurs at radii from 2.3 to 3.7 AU for AGB carbon stars in the 1.1-5 M☉ range. This analysis also yields time intervals available for graphite growth that are on the order of a few years. By considering the luminosity variations of carbon stars, we show that grains formed during minima in the luminosity are likely to be evaporated subsequently, while those formed at luminosity maxima will survive. We calculate strict upper limits on grain sizes for graphite and TiC in spherically symmetric AGB outflows. Graphite grains can reach diameters in the observed micron size range (1-2 μm) only under ideal growth conditions (perfect sticking efficiency, no evaporation, no depletion of gas species contributing to grain growth), and then only in outflows from carbon stars with masses ≲2.5 M☉. The same is true for TiC grains that are found within presolar graphite, which have mean diameters of 24 ± 14 nm. In general, the mass-loss rates that would be required to produce the observed grain sizes in spherically symmetric outflows are at least an order of magnitude larger than the maximum observed AGB carbon star mass-loss rates. These results, as well as pressure constraints derived from equilibrium thermodynamics, force us to conclude that presolar graphite and TiC must form in regions of enhanced density (clumps, jets) in AGB outflows having small angular scales. As shown in the companion paper by Croat et al., the enrichment of 12C in many AGB graphites, and the overabundances of the s-process elements Mo, Zr, and Ru in the carbides found within them, often greatly exceed the values observed astronomically in AGB outflows. These observations not only lend further support to the idea that the outflows are clumpy, but also imply that the outflowing matter is not well mixed in the circumstellar envelope out to the radii where grain condensation takes place.

Titanium carbide particles as pre-solar grains

Focusing on the growth of metal carbide particles and the formation of pre-solar grains, a new attempt has been made for titanium carbide (TiC) systems. Using the noble gas evaporation method, we succeeded in producing TiC core (50-nm) carbon mantle (2-nm) grains of the same core size as pre-solar grains. The infrared spectrum has broad absorption features at 9.5 and 12.5 µm. It was also found that these absorption peaks became weaker by an increase to 15 nm of carbon mantle layer. The determination method of the contact angle of carbon on the TiC grain has been developed using a high-resolution electron microscopic technique. The contact angles between TiC and carbon were 22. ◦ 8 ± 0. ◦ 7 and 24. ◦ 0 ± 0. ◦ 4 on the (111) and (100) TiC

Si-induced twinning of TiC and formation of Ti 3SiC 2 platelets

Effects of silicon in titanium carbide (TiC) have been investigated using high-resolution electron microscopy combined with high-spatial-resolution analytical electron microscopy. The results demonstrate that Si can reduce the twin boundary energy of TiC, leading to the formation of a lot of two-dimensional (2D) defects in TiC grains containing Si. These defects were identified as microtwins of four (111) spacings thick and structural-related Ti 3SiC 2 platelets of only one unit cell thick. The twin-stabilizing effect of Si is discussed in terms of coordination environments of Si. Very thin Ti 3SiC 2 platelets are formed, accompanied by the segregation of Si atoms and carbon vacancies to the twin boundaries. Microtwins and Ti 3SiC 2 platelets were found to grow in 2D with Si totally confined in the defects.

Room temperature deposition of titanium carbide thin films using dense plasma focus device

Thin films of titanium carbide (TiC) were deposited on 304-stainless steel substrates using a dense plasma focus device. The conventional hollow copper anode of the 3.3 kJ Mather type plasma focus device was replaced by solid titanium anode for deposition of TiC thin films. The argon–acetylene admixture (in 7:3 ratio) was used as the filling gas at a pressure of 1.5 mbar. Substrates were placed along the anode axis at a distance of 11.5 cm from the top of the anode. Thin films of TiC were deposited using different numbers of focus shots, like 10, 20 and 30, at room temperature substrates. Deposited films were analyzed for their structure, surface morphology, surface profile, elemental composition and distribution using X-ray diffraction (XRD), scanning electron microscopy (SEM), surface profiling and energy dispersive X-ray spectroscopy (EDX). XRD patterns in all three cases are found to have diffraction peaks for (111), (200), (220), (311) and (222) TiC crystalline planes. Scanning electron micrographs show a smooth film surface with increasing clustering of TiC grains with the increase in number of focus deposition shots. EDX spectra confirm the presence of expected constituent elements with the gradual increase in TiK α peak (of the TiC thin film) relative to FeK α peak (of the substrate) with increasing numbers of focus deposition shots due to increasing film thickness. EDX mapping reveals a uniform distribution of TiC over the substrate surface. These results confirm the first ever deposition of TiC thin films using a dense plasma focus device.

Titanium carbide nanocrystals in circumstellar environments.

Meteorites contain micrometer-sized graphite grains with embedded titanium carbide grains. Although isotopic analysis identifies asymptotic giant branch stars as the birth sites of these grains, there is no direct observational identification of these grains in astronomical sources. We report that infrared wavelength spectra of gas-phase titanium carbide nanocrystals derived in the laboratory show a prominent feature at a wavelength of 20.1 micrometers, which compares well to a similar feature in observed spectra of postasymptotic giant branch stars. It is concluded that titanium carbide forms during a short (approximately 100 years) phase of catastrophic mass loss (>0.001 solar masses per year) in dying, low-mass stars.

Optical properties of alumina titanium carbide sliders used in rigid disk drives

A common material for read-write sliders is a composite of alumina (Al(2)O(3)) and titanium carbide (TiC), with a grain size of the order of 1 mum. I derive the effective complex reflectivity of this material, using scalar diffraction theory and the known indices of refraction of Al(2)O(3) and TiC. The effective reflectivity is a function of the relative surface area of the exposed TiC grains as well as of the numerical aperture of the collection optics. The theory resolves several known discrepancies between ellipsometry and reflectometry of Al(2)O(3)-TiC. The theory also predicts a systematic error in the phase shift on reflection calculation. These results are of considerable interest for surface shape metrology of the slider as well as for optical flying-height testing and control of pole-tip recession.

In‐situ SEM observation of the fracture behaviour of titanium carbide/nickel aluminide composites

A range of experimental titanium carbide (TiC)/nickel aluminide (Ni3Al) composites have been developed. The Ni3Al content has been varied from 15 to 40 vol.%, for two different alloy compositions. The fracture behaviour of these composites was assessed in situ, within the chamber of a field emission gun scanning electron microscope. An applied moment double cantilever beam test geometry was employed, which allowed determination of the materials fracture resistance curve (or R‐curve), while simultaneously monitoring crack–microstructure interactions. All of the tested materials exhibited a pronounced R‐curve, with fracture resistance increasing with increasing crack length, up to a steady‐state plateau value. The highest steady‐state toughness values (up to 15 MPa m−1/2) were obtained for composites prepared with the highest Ni3Al binder content. In addition, these materials exhibited the highest strength and Weibull modulus. In‐situ examination of the fracture process demonstrated considerable crack wake bridging by ductile Ni3Al ligaments, with bridging zone length of >100 μm often observed. The use of a displacement mapping technique has demonstrated that Ni3Al plastic deformation is highly localized around the crack, typically within one TiC grain width (i.e. ≈3–5 μm) away from the crack.

窒素を含む炭化チタン基サーメットに観察される白点の生成機構

It has been known that white spots frequently appear in SEM structure of titanium carbide (TiC) grains in nitrogen contained TiC based cermets. The formation of the white spots was studied as functions of alloy system, alloy composition and sintering conditions, using specimens having coarse TiC grains in the structure.It was found that the white spots appeared only in TiC-TiN (or Ti(C, N))-Mo2C-Ni alloy system, and the formation of white spots varied according to the above factors. It was assumed in TiC-TiN-Mo2C-Ni alloy system that TiC grains did not easily dissolve in liquid binder at the sintering temperature, because molybdenum atoms tended to diffuse in TiC grains to form TiC-Mo2C solid solution. Consequently, TiC grains had to dissolve with making many slits around the periphery of TiC grain, resulting in the liquid-infiltration in the slits and the formation of white spots.

Optimization of the process of manufacture of diamond-containing composite materials based on titanium carbide-steel alloys

A study was made of the conditions of production of tungsten-free composite materials by sintering in a high-pressure chamber and in vacuum. Good-quality nonporous specimens of titanium carbide-steel materials cannot be produced by hot pressing in graphite dies. The hardness of materials sintered in a HPC is higher (81–86 HRA) than that of materials sintered in vacuum (75–82 HRA.). Heat treatment slightly lowers it (to 77–85 HRA). The highest wear resistance is exhibited by vacuum-sintered materials. In alloys sintered in a HPC a directional orientation of the steel binder with titanium carbide grain inclusions was observed. In service tests the properties of composition diamond-containing materials based on titanium carbide-steel alloys were found to match those of Tvesal alloys-diamond-containing composites based on a tungsten-group hard metal.

FERRO-TIC DN-1

Abstract FERRO-TIC DN-1 is comprised of a dispersion of extremely hard, inert titanium carbide grains in a special age-hardenable nickel-aluminum alloy matrix. It is characterized by excellent resistance to corrosion by strong chlorides. Its maximum operating temperature is 900 F. This datasheet provides information on composition, physical properties, and hardness. It also includes information on corrosion resistance as well as heat treating, machining, surface treatment, and powder metal forms. Filing Code: Ni-241. Producer or source: Chromalloy Metal Tectonics Company.

Tungsten-free hard alloys based on binary carbides

1. A study was made of the sintering behavior and structure of hard alloys based on titanium carbide alloyed with vanadium, niobium, and tantalum carbides. 2. The optimum conditions for the sintering of these hard alloys in a vacuum are a temperature of 1320–1350°C and an isothermal heating time of 30 min. 3. It is shown that the growth of titanium carbide grains during sintering is strongly affected by alloying with the above-mentioned carbides (the extent of the effect increasing in the order TaC < NbC < VC), which is linked with differences in the extent to which the resultant binary carbides are soluble in the binder when liquid.

FERRO-TIC HT-2

Abstract FERRO-TIC HT-2 is a dispersion of extremely hard titanium carbide grains in an austenitic, heat-resistant, age-hardenable, iron-nickel-chromium alloy matrix. It exhibits good strength and good resistance to oxidation, corrosion, carburization and wear up to 1350 F. This datasheet provides information on composition, physical properties, hardness, and elasticity as well as creep. It also includes information on corrosion resistance as well as heat treating, machining, joining, surface treatment, and powder metal forms. Filing Code: SS-322. Producer or source: Chromalloy American Corporation, Sintercast Division.

FERRO-TIC HT-6

Abstract FERRO-TIC HT-6 is comprised of a dispersion of extremely hard, inert titanium carbide grains in a precipitation-hardenable, nickel-base matrix. It provides a combination of oxidation, corrosion and wear resistance unavailable in other materials for tools and many other uses. This datasheet provides information on composition, physical properties, hardness, and elasticity as well as creep. It also includes information on high temperature performance and corrosion resistance as well as heat treating, machining, surface treatment, and powder metal forms. Filing Code: Ni-207. Producer or source: Chromalloy American Corporation.