Polycrystalline TiC Research Articles

Diffusion and retention of helium in titanium carbide

The knowledge of helium migration in TiC is an important issue due to its possible use as fuel coating in fission reactors and as first wall material coating in fusion reactors. Helium release measurements and diffusion coefficient calculations of helium in polycrystalline TiC have been carried out in the temperature range (1000–1600°C) for the time period of 2h. Polished bars of TiC were implanted with 3MeV 3He+ ions in normal incidence at a dose of 5×1020at./m2 at room temperature. Helium depth profile was measured at each step using the 3He(d, p0)4He nuclear reaction by varying the incident deuteron energy from 900 to 1800keV. Effective diffusion coefficients vary from 4.20×10−18 to 2.59×10−17m2s−1 and activation energy values obtained are in the range 0.8–2.5eV. Due to scarce availability of stoichiometric TiC, challenges in this study came from native vacancies present in the samples. The helium distribution and its release were affected by the presence of grain boundaries. He is considered to undergo two distinct populations into the sample and different values of diffusion coefficient have been determined for each population.

Effects of Pore Sealing on Self-Formation of Ti-Rich Barrier Layers in Cu(Ti)/Porous-Low-k Samples

To investigate effects of pore seals on self-formation of Ti-rich barrier layers, Cu(1 at. % Ti) alloy films were deposited on porous SiOxCyH (low-k) dielectric layers in samples with and without about 6.5-nm-thick SiCN pore seals. Self-formed Ti-rich barrier layers were formed on the porous low-k layers after annealing in Ar for 2 h at 400–600 °C. The samples without pore sealing had a rough interface, indicating that Ti atoms reacted with the porous low-k layers at the pore surfaces. In contrast, the pore-sealed samples had a smooth interface. The Ti-rich barrier layers in the samples consisted of amorphous Ti oxides. In addition, polycrystalline TiC and amorphous TiN and TiC were observed to be formed beneath the Cu(Ti) alloy films in the annealed samples without pore sealing and pore-sealed samples, respectively. Note that Ti segregation at the interface was divided into two layers, suggesting that the Ti-rich barrier layers self-formed by the reaction of Ti atoms with the pore sealing and porous low-k layers are separated. The resistivity of the pore-sealed samples was lower than that of the samples without pore sealing. This is attributed to lower residual Ti atoms in the alloy films and coarser columnar grains in the pore-sealed samples.

Ti-Rich Barrier Layers Self-Formed on Porous Low-k Layers Using Cu(1 at.% Ti) Alloy Films

To investigate the applicability of the technique of barrier self-formation using Cu(Ti) alloy films on porous low-k dielectric layers, Cu(1 at.% Ti) alloy films were deposited on porous SiOCH (low-k) dielectric layers in samples with and without ~6.5-nm-thick SiCN pore seals. Ti-rich barrier layers successfully self-formed on the porous low-k layer of both sample types after annealing in Ar for 2 h at 400°C to 600°C. The Ti-rich barrier layers consisted of amorphous Ti oxides and polycrystalline TiC for the samples without pore sealing, and amorphous TiN, TiC, and Ti oxides for the pore-sealed samples. The amorphous TiN originated from reaction of Ti atoms with the pore seal, and formed beneath the Cu alloy films. This may explain two peaks of Ti segregation at the interface that appeared in Rutherford backscattering spectroscopy (RBS) profiles, and suggests that the Ti-rich barrier layers self-formed by the reaction of Ti atoms with the pore seal and porous low-k layers separately. The total molar amount of Ti atoms segregated at the interface in the pore-sealed samples was larger than that in the samples without pore sealing, resulting in lower resistivity. On the other hand, resistivity of the Cu alloy films annealed on the porous low-k layers was lower than that annealed on the nonporous low-k layers. Coarser Cu columnar grains were observed in the Cu alloy films annealed on the porous low-k layers, although the molar amount of Ti atoms segregated at the interface was similar in both sample types after annealing. The cause could be faster reaction of the Ti atoms with the porous dielectric layers.

Nano‐TiC obtained through a reaction of MWCNTs with Zr(Y,Ti)O2

The zirconia nanopowder stabilized with 2.5 mol% Y(2)O(3) and doped with 18 mol% TiO(2) (Zr(Y,Ti)O(2)) was homogenized with 5.2 wt% multiwall carbon nanotubes (MWCNT) through colloidal processing. The resultant mixture was heat-treated for 2 h at 1200 degrees C in vacuum under a pressure of 5 x 10(-4) mbar. The microstructure characterization was performed using the TECNAI FEG (200 kV) SuperTWIN transmission electron microscope, equipped with the integrated EDAX detector. The TEM observations of the as-received samples showed single strands of the carbon nanotubes uniformly dispersed among zirconia crystallites. Heat treatment of the Zr(Y,Ti)O(2)-MWCNT mixture caused the transformation of carbon nanotubes into polycrystalline TiC nanofibres and nanorods as confirmed by both the energy dispersive X-ray spectroscopy microanalysis and the high-resolution electron microscopy (HREM) observations. Relying on the above, a mechanism of the TiC in situ crystallization controlled by carbon diffusion through the newly formed TiC phase was discussed.

Reactive wetting of polycrystalline TiC by molten Zr55Cu30Al10Ni5 metallic glass alloy

The isotherm wetting and spreading behaviors of polycrystalline TiC by molten Zr55Cu30Al10Ni5 alloy were investigated at 1133 to 1253 K in a vacuum by using a modified sessile drop method. The system displays good wettability with the initial and final stable contact angles of 44 to 50° and 10 to 14°, respectively, mildly depending on the temperature. The spreading kinetics follows well defined exponential functions and could be described by a molecular dynamic model. On the other hand, a ZrC reaction layer was formed at the interface. The wetting was primarily promoted by the Zr adsorption at the triple junction and then by the formation of the reaction layer.

Effect of interparticle interaction on the low temperature oxidation of CO over size-selected Au nanocatalysts supported on ultrathin TiC films

This work aims to get insight into the influence of interparticle interactions on catalysis. The low temperature CO oxidation is used as a model reaction. A strong dependence of the catalytic activity and stability of gold nanoparticles uniformly dispersed on polycrystalline TiC films was observed as a function of the interparticle distance. Two samples with similar height distributions (∼2 nm), but with different average interparticle distances (∼30 and ∼80 nm), were synthesized using diblock copolymer encapsulation. Their chemical reactivity was investigated by temperature programmed desorption (TPD), and reactive coarsening and subsequent deactivation was observed for the sample with the smallest interparticle distance. The system with the largest average interparticle distance showed higher stability towards agglomeration and longer lifetime.

Reactions of water and ethanol with polycrystalline TiC surfaces

The adsorption and reaction of water and ethanol with polycrystalline TiC coatings have been investigated and compared with those of the nonpolar (100) face of single crystal TiC. This work is pursued to develop a fundamental understanding of the surface bonding and reaction properties, thus enabling the use of TiC as a tribological coating material. Temperature-programmed desorption has been used to characterize the desorption behavior of these model adsorbates as well as that of products resulting from their reaction with the TiC surface. Following adsorption at 100K, molecular desorption as well as desorption of reaction products is evident for both water and ethanol. Approximately 70% of the water in the monolayer is judged to irreversibly react with the TiC surface, producing a surface oxide and gaseous hydrogen and carbon monoxide. Approximately 92% of the ethanol in an adsorbed monolayer reacts, predominantly producing gaseous ethene. These results are similar to those on TiC(100) surfaces, although a greater extent of surface reactivity is observed on the polycrystalline surface.

Titanium carbide film deposition on silicon wafers by pulsed KrF laser ablation of titanium in low-pressure CH4and C2H2atmospheres

We report on the deposition of thin titanium carbide films on 60 mm and 100 mm Si wafers by KrF laser ablation of titanium targets in low-pressure (0.1 Pa) CH 4 and C 2 H 2 atmospheres, and on their characterization. The targets were titanium foils (purity 99.6%). Si (111) wafers, 60 and 100 mm in diameter, were used as substrates. Film characteristics (thickness, composition and crystalline structure) were studied as a function of the carbon-containing gas (C 2 H 2 or CH 4 ), laser fluence (4 or 6 J/cm 2 ), substrate temperature (20 or 250 °C) and target-to-substrate distance (70–120 mm). Continuous, well adhesive polycrystalline TiC films were deposited even without any heating of the substrate. Films deposited in C 2 H 2 ambient atmosphere are better crystallized and less prone to surface oxidation with respect to films deposited in CH 4 atmosphere, in otherwise identical conditions.

SiC p/Ti6Al4V functionally graded materials produced by laser melt injection

With a well-controlled laser melt injection (LMI) process, for the first time the feasibility is demonstrated to produce SiC particles (SiC p) reinforced Ti6Al4V functionally graded materials (FGMs). SiC p are injected just behind the laser beam into the extended part of the laser melt pool that is formed at relatively high beam scanning velocities. The process allows for the minimization of the decomposition reaction between SiC p and Ti6Al4V melt, and also leads to FGMs of SiC p/Ti6Al4V instead of a homogeneous composite layer on Ti6Al4V substrates. An injection model is designed based on the temperature/viscosity field of the laser pool for a deeper understanding of the mechanism of formation of the FGMs with LMI. The model is based on finite element calculations of the temperature field in the melt pool, physical considerations of the LMI process and it is supported by experimental observations. Three types of reaction layers are observed around SiC p, namely a thin monocrystalline TiC layer, a cellular polycrystalline TiC layer and a thick mixed layer of TiC with Ti 5Si 3. Among them, only the monocrystalline TiC layer exhibits particular orientation relationships (ORs) to the SiC p lattice, i.e. (111) TiC∥(0001) SiC and 〈110〉 TiC ∥〈1 1 ̄ 00〉 SiC or (111 ) TiC ∥(10 1 ̄ 2 ) SiC and 〈1 1 ̄ 0〉 TiC ∥〈1 2 ̄ 10〉 SiC . These two kinds of TiC reaction layers act as a barrier against the interfacial reaction and its swift formation during rapid cooling hinders the dissolution of SiC p in the Ti-melt.

Microstructure and properties of low friction TiCC nanocomposite coatings deposited by magnetron sputtering

The objective of nanocomposite coatings combining hard and lubricant phases is the development of advanced multi-functional protective thin films showing abrasion resistance, and simultaneously, low friction. Up to now, no clear relation between constitution, microstructural properties and performance of such nanocomposite coatings based on dry lubricants like carbon or MoS 2 has been evaluated. Deposition techniques, constitution, properties and performance of magnetron-sputtered nanocomposite coatings in the TiCC system are presented. The Vickers hardness could be optimized to values of polycrystalline TiC thin films, and at the same time, low friction coefficients against steel, similar to diamond-like amorphous carbon, could be realized. The mechanical properties and the tribological behavior of these thin films are related to the chemical composition and the microstructure of these advanced materials, characterized by electron microprobe analysis, Auger electron spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and high resolution transmission electron microscopy.

Weak Interaction of Oxygen with Some Refractory Carbides

The reactivity of NbC (single crystal and polycrystalline), TiC (single crystal and polycrystalline), and polycrystalline ZrC in the temperature range from ambient to 1020°C and at oxygen partial pressures from 0.07 to 9 Pa is reported. The reactivities of the principal (hkl) planes of TiC as well as the polycrystal are also measured at 0.8 Pa of The reactivity ratio order is 1.0, 1.2, and 1.9, respectively, for (111), (100), and (110) planes. Under these conditions, laths at right angle of epitaxial rutile were observed. The comparison of the reactivity between NbC(100) and polycrystalline NbC has been determined and some tentative data are given on the reactivities of the other planes. The reactivity at higher oxygen partial pressures was also measured for TiC(111) and in these conditions a well-defined TiC-rutile ceramic to ceramic joint has been obtained. The reactivity and in situ electrical resistivity measurements on polycrystalline TiC and ZrC, both as received and high temperature, high vacuum treated, are presented. Large differences in the reactivity hystereses were found. The same result was not found in the behavior of the resistivity. © 2001 The Electrochemical Society. All rights reserved.

Raman light scattering in nanoporous carbon obtained from silicon and titanium carbides

A study is reported on the Raman spectra of nanoporous carbon prepared in a chemical reaction from polycrystalline α-SiC and TiC. The spectra are shown to be of a multicomponent nature, which distinguishes this group of materials from graphites and disordered carbon structures. A series of low-frequency modes are detected. Anisotropy and dispersion effects are revealed. The results obtained argue in favor of a cluster structure of nanoporous carbon and size quantization of the electronic and vibrational spectra in carbon nanoclusters. The main structural elements of the nanoclusters in the porous framework are small fragments of bent or broken graphene sheets. The presence of fragments close in structure to strained cubic or hexagonal diamond is observed in a number of cases.

Functionally Graded Materials produced with High Power Lasers

AbstractWith a well-controlled laser melt injection (LMI) process, for the first time the feasibility is demonstrated to produce SiC particles (SiCp) reinforced Ti6Al4V functionally graded materials (FGMs). SiCp are injected just behind the laser beam into the extended part of the laser melt pool that is formed at relatively high beam scanning velocities. The process allows for the minimization of the decomposition reaction between SiCp and Ti6Al4V melt, and also leads to FGMs of SiCp/Ti6Al4V instead of a homogeneous composite layer on Ti6Al4V substrates. An injection model is designed based on the temperature/viscosity field of the laser pool for a deeper understanding the mechanism of formation of the FGMs with LMI. The model is based on finite element calculations of the temperature field in the melt pool, physical considerations of the LMI process and it is supported by experimental observations. Three types of reaction layers are observed around SiCp, namely a thin monocrystalline TiC layer, a cellular polycrystalline TiC layer and a thick mixed layer of TiC with Ti5Si3. Among them, only the monocrystalline TiC layer exhibits particular orientation relationships to the SiCp lattice, i.e. (111)TiC//(0001)SiC and <110>TiC//<1100>SiC or (111)TiC // (1012)SiC and <110>TiC//<1210>SiC. These two kinds of TiC reaction layers act as a barrier against the interfacial reaction and its swift formation during rapid cooling hinders the dissolution of SiCp in the Ti-melt.

Apparent oxygen solubility in refractory carbides

The occurrence of an apparent solubility of oxygen in polycrystalline NbC, TiC, VC and ZrC is discussed. This is shown by experiments in which the oxygen consumed by the sample is directly measured as a function of temperature in an argon stream at 1.6 bar (rel) where the oxygen partial pressure was as low as 0.8 Pa. The parameter Γ, as the ratio between the weight change of the sample and the number of moles of oxygen consumed, has been proposed to discriminate the nature of the processes related to the gas/solid interaction. The limit values of Γ, theoretically expected to be 0 and 32 g mol −1, mean that the gas/solid interaction changes from a surface reaction without any weight change to a complete retention of oxygen in the solid. Intermediate values indicate the formation of the oxide at a given stoichiometry as found experimentally as a function of the oxygen partial pressure.

Properties of TiC thin films grown by pulsed laser deposition

Titanium carbide thin films have been deposited on both (100) silicon and fused silica substrates by pulsed laser ablating a polycrystalline TiC target. At a KrF excimer laser intensity of about 8×10 8 W/cm 2, the pulsed laser deposition (PLD) of TiC films was investigated at substrate deposition temperatures ranging from 25 to 600°C. The structure, surface composition, electrical resistivity, stress, work function and morphology of the PLD TiC films were characterized as a function of the deposition temperature. While all the deposited TiC films are polycrystalline with a preferred (111) orientation, both the magnitude of their compressive stress and their resistivity were found to decrease gradually as a function of the deposition temperature, from −7 to ∼−3 GPa and from 140 to 80 μΩ cm, respectively. The X-ray photoelectron spectroscopy (XPS) analysis revealed that oxygen (at an average level of ∼10 at.%) is incorporated into the TiC films where it substitutes for C. The surface composition of the films is found to be stoichiometric with an average Ti/(C+O) ratio of 0.98±0.06. The deposited TiC films exhibited low work functions in the (3.74–3.94) eV range. Their surface morphology is characterized by a very smooth surface on which some particulates are present. The density of these particulates (of which typical lateral dimension is about 1 μm and height is about 100 nm) is of the order of 2 per 100 μm 2. The properties of these PLD TiC films are discussed in view of their use as electron injecting electrode materials for organic electroluminescent devices.

Positron studies of polycrystalline TiC

The mean positron lifetime tau , positron diffusion length L, and the positron and electron work functions ( phi + and phi -) for polycrystalline TiC have been experimentally determined. The results were tau =160(2) ps, L+=138(27) nm and phi -=3.96(0.08) eV; phi + was shown to be almost certainly positive. These results strongly support the suggestion from recent first-principles electronic structure and positron state calculations that positions are trapped by and annihilate in metal vacancies in this material. XPS measurements indicate that the trapping sites may be predominantly in thin carbon-rich layers between grains, a picture which may also explain the long near-surface diffusion length.

自己燃焼高圧ホットプレス法で作製したＴｉＣ／ＳｉＣ複合焼結体

Mixtures of Ti-C and Si-C powders respectively equimolar were mixed in various ratios. The final mixture was molded by using an pressure-resistant metallic mold whose inner wall was covered with a carbon felt for insulation. The molded mixture, once set in the mold, was ignited by a tungsten heater and, then, instantaneously uniaxially compressed of 1 GPa (SHS/HP processing). SEM and TEM observations were carried out to get insight in the microstructures obtained for the TiC/SiC composites. Two separated phases, namely SiC and TiC, were present in the composites prepared from Ti-C rich mixtures. In these cases, aggregates of SiC grains, often including some large pores, were found surrounded by the bulk polycrystalline TiC body. On the other hand, fine dispersions of TiC and SiC grains were obtained when nearly equimolar mixtures of Ti-C/Si-C were employed. In this latter case, a maximum value of 28 GPa for the Vickers hardness was measured.

TiCの延性・脆性遷移挙動に及ぼすNbおよびMo添加の効果

TiCの延性・脆性遷移挙動に及ぼすNbおよびMo添加の効果

Alternate Titanium Source Compounds for CVD of Ti/TiC Coatings

ABSTRACTCVD experiments were conducted using (Me3SiCH2)4Ti, Bis(2,4-dimethylpentadienyl) titanium, Cl3TiMe, (Me3SiCH2TiCl3 to evaluate their potential as Ti precursor compounds. Only Me3SiCH2TiCl3 was suitable for atmospheric CVD applications. Uniform thin films of polycrystalline TiC were deposited using Me3SiCH2TiCl3 in an argon ambient between 700 °C and 800 °C. A mechanism involving initial loss of Me3SiCl to generate a titanium carbene intermediate is proposed. Thin films of TiC deposited on Si[111] were characterized using XRD and AES. Depth profile line shape analysis showed only TiC and elemental Si in the interfacial region. XRD indicates some titanium silicide is formed at 800 °C. In a hydrogen ambient, hydrogenolysis of the alkyl group occurs and very poor film growth results were obtained.

ChemInform Abstract: Electrochemical Characteristics of Amorphous Titanium Carbide Films Produced by Low‐Temperature Metal‐Organic Chemical Vapor Deposition (MOCVD).

AbstractA comparative potentiodynamic study is carried out for amorphous TiC films prepared by either electron beam vaporization (EBV) or by MOCVD using Ti(bipy)3 or (Me3CCH2)4Ti and for bulk polycrystalline TiC.