Ti TiC Research Articles

Crystal-chemistry of the Ti 3AlC 2 and Ti 4AlN 3 layered carbide/nitride phases—characterization by XPS

The M n+1 AX n layered carbide/nitride-derived phases, where M is an early transition metal, A is an A-group element and X is N or C, have an unusual combination of mechanical, electrical and thermal properties. The surface and crystal-chemistries of two members with n=2 and 3 have been investigated by X-ray photoelectron spectroscopy. The results show that the constituent species are characterized by low binding energies, sometimes exceptionally so. The energies are 281.0–281.5 and 396.9 eV, respectively, for C 1s and N 1s, both of which are at, or below, the lowest values measured for carbides and nitrides. Similarly the Ti 2p energies, in the range 454.0–454.7 eV, are comparable to that of Ti metal and TiC, while the energy of the Al 2p, 72.0 eV, is lower by ca. 0.8 eV than that for Al metal. The signature of the XTi 6 octahedral units in the stacking sequence is reminiscent of the corresponding units in TiN, and it is found that a decrease in Ti 2p binding energy is correlated with decrease in average X-Ti bond length. The low binding energies of the A-type species, Al and Si, in planar coordination suggest that binding and thus screening may be derived from out-of-plane interactions. Results relevant to oxidation arising from exposure to air have been obtained.

In situ formation of titanium carbide in titanium powder compacts by gas–solid reaction

Porous titanium compacts of fine and coarse sponge titanium powders were reacted with methane gas to produce Ti–TiC in situ composites. The kinetics of titanium carbide formation during the reaction were studied in relation to powder size, reaction temperature and time, and methane flow rate. The titanium carbide was initially formed as a layer around each titanium powder and the rate of formation was found to be diffusion-controlled. Titanium hydride was also formed during the reaction but was easily removed by post-vacuum annealing. A significant reduction of chlorine content in the compact also resulted during the processing. High temperature vacuum sintering could densify the reacted compacts to over 95% theoretical density and, at the same time, alter the layered titanium carbide phase into rounded particles. It was possible to produce fully dense titanium base composites containing up to 30 vol% by the present gas–solid reaction-based processing.

The development of a functionally graded TiC–Ti multilayer hard coating

A functionally graded transition zone between a hard TiC coating and a WC–Co substrate, e.g. a cutting tool, can be formed over the range composition of the titanium carbide phase that extends from Ti 2C to TiC. The transition zone is formed by sputter deposition of a multilayer stack of nanometric TiC and Ti layers. The composition gradient within the carbide layer is generated by varying the relative thickness of the as-deposited Ti and TiC layers. A subsequent short diffusion treatment eliminates the interfaces between the adjacent layers, yet maintains an overall carbon composition gradient across the thickness of the coating. The relative thickness of the individual sputtered layers is adjusted to yield a low carbon composition in the coating close to the substrate and a stoichiometric composition near the external surface. The composition profile within the coating can be further optimized with respect to residual stresses that arise during cooling after the diffusion anneal. In the present work, different graded Ti–TiC profiles were deposited on WC–Co substrates in two steps. First, a 0.5-μm graded Ti–TiC multilayer was deposited followed by a 2.5-μm outer layer stoichiometric TiC. Scratch tests, carried out on the as-deposited and on the annealed coatings showed that the critical load and the wear resistance depended on the concentration profile within the transition layer.

THERMOELECTRIC PROPERTIES OF Ti-DOPED SiC/TiCx COMPOSITE SYNTHESIZED BY TPPP METHOD

To improve thermoelectric properties, we attempt to dope Ti into SiC-based composite by transient plastic phase process (TPPP) method. The final result is composed of the functional phase SiC and the reinforcement phases TiC x and TiSi 2. The process of doping is the diffusion of Ti in TiC x solid–solution into SiC grain at high temperature. When the initial SiC is α-type of 5 μm size, the Seebeck coefficient S is less than 10 μV/K at room temperature. SEM photograph shows the reason being that doping is very weak. We change the initial SiC to the β-type of 90 nm size to aid doping. It is observed that S can be significantly improved to 46.3 μV/K at room temperature. When the temperature rises, the improvement is even greater. Measurements of the lattice parameter of β- SiC show that the parameter parallel to the Si–C layer is almost unchanged and the parameter perpendicular to the Si–C layer increases by about 0.48%, which demonstrated that Ti has been successfully doped into the SiC grain and exists as interstitial impurities.

Hardness measurements of Ti and TiC multilayers: a model

Microhardness measurements of thin films have to face the problem of the influence of the substrate on the measurement. Numerous models which take into account this behaviour are available in the literature. When the film is composed of several layers of different properties, it is more difficult to solve this problem because of the multiple influences of the different layers and the substrate. Little work on this subject has been already done; we propose here an extension to multilayers of two models: that of Jönsson and Hogmark, based on the relative deformed areas under the indent, and a model we have developed on the basis of plastically deformed volumes in the substrate and in the film. Starting from the hardness determination of Ti and TiC monolayer films, it is shown that it is possible to use either one or the other model to determine the composite superficial hardness of multilayer Ti–TiC films.

Effect of interlayer composition on the tribological properties of TiC/Ti(C x, N 1− x)/TiN anti-abrasive multi-layer coatings

This paper presents an investigation of the durability of wear-resistant multi-layer coating TiC/Ti(C x N 1− x )/TiN deposited by vacuum-arc method. The coatings selected for the investigations were prepared by introducing a mixture of C 2H 2 and N 2 gas in different proportions, in the deposition chamber, during the arc-deposition process. A three-layer coating TiC/Ti(C x N 1− x )/TiN was selected as a model system and the effects examined of the crystallographic match of the constituent layers in the TiC–Ti(C x N 1− x ) and Ti(C x N 1− x )–TiN interfaces on their wear resistance. The authors have used two methods to determine anti-wear properties of selected coatings: laboratory test was performed using rotating sphere test and performance test on industrial scale. The present investigations show that the crystallographic match in the TiC–Ti(C x N 1− x ) and Ti(C x N 1− x )–TiN interfaces changed in a nonlinear manner and depend on lattice parameter and texture of this materials. Anti-wear properties for coating TiC/Ti(C x N 1− x )/TiN changed in a nonlinear manner too. The largest value of wear-resistance occurred where working atmosphere for the Ti(C x N 1− x ) layer was C 2H 2/N 2=75%/25%. The minimum of wear resistance occurred for working atmosphere for the Ti(C x N 1− x ) : C 2H 2/N 2=50%/50%.

Influence of chemical effect on the K β-to-K α X-ray intensity ratios of Ti, V, Cr and Fe in TiC, VC, CrB, CrB 2 and FeB

K β-to-K α X-ray intensity ratios of Ti, V, Cr and Fe have been measured in pure metals and in the compounds of TiC, VC, CrB, CrB 2 and FeB following excitation by 59.54 keV γ-rays from a 200 mCi 241Am point-source. Comparison of the measured K β-to-K α X-ray intensity ratios with the multiconfiguration Dirac–Fock calculation indicates significant change in the 3d electron population of Ti in TiC and Cr in CrB and CrB 2 from their pure metal values and almost no change for V in VC and Fe in FeB. In TiC we have found a transfer of 0.65±0.16 electrons from the 3d state of Ti whereas for CrB and CrB 2 the 3d electron population of Cr increases by 0.60±0.30 and 0.75±0.30 electrons, respectively, over the pure metal value. Although our charge transfer result for TiC is closer to the prediction of the APW band structure calculations no firm conclusion can be made from our VC result. Our result for the relative K β-to-K α ratio of VC with respect to pure V does not agree with the previously reported experimental result of Chang et al. (J. Phys. B: At. Mol. Opt. Phys. 27 (1994) 5251). Our results for CrB and CrB 2 predict transfer of electrons from boron to 3d band of Cr in agreement with some of the earlier published results of magnetic and Hall effect measurements.

Chemical interaction between carbon and titanium dissolved in liquid tin: crystal structure and reactivity of Ti 2 SnC with Al

Abstract Chemical interaction between carbon and titanium dissolved in liquid tin was studied at temperatures higher than 1000°C. The phase equilibria in the ternary system graphite–titanium–tin were investigated by thermal analysis, metallography, X-ray diffraction and electron microprobe analysis. The isothermal section at 1200°C is proposed. At this temperature, carbon can react to yield a binary phase, TiC, or a ternary phase, Ti 2 SnC. The structure of Ti 2 SnC is proposed on the basis of powder diffraction X-ray data (space group: P6 3 /m.m.c.; hexagonal axes a =0.31626 nm, c =1.36789 nm). Some experiments realized by immersion of T300 fibres in Sn–Ti alloys show that the chemical reaction leads to either a single layer of TiC or a double-layer, TiC–Ti 2 SnC. The results demonstrate that the ternary phase is not stable in liquid aluminium.

The influence of the tribological properties of the crystallographic match of TiC⧹Ti(C xN 1-x)⧹TiN multi-layers

The influence has been studied of the crystallographic match of vacuum-arc deposited layers in anti-abrasive multi-layer films on their tribological properties. A three-layer coating (TiC⧹Ti(C x N 1−x )⧹TiN) was selected as a model system and the effects examined of the crystallographic match of the constituent layers in the TiC–Ti(C x N 1−x ) and Ti(C x N 1−x )–TiN interfaces on their sliding-wear-resistance. The sliding-wear characteristics were determined using the sliding friction of a steel ball on the surface of the selected sample followed by measurement of the volume of removed material. The sliding-wear-resistance was taken as the durability indicator-γ 60. It was found that the sliding-wear intensity of the TiC⧹Ti(C x N 1−x )⧹TiN multi-layer as a function of the composition of the working atmosphere for the Ti(C x N 1−x ) deposition changed in a nonlinear manner. The largest value of sliding-wear-resistance (durability indicator γ 60 = 82×10 [3][mm −3]) occurred for coating TiC⧹Ti(C x N 1−x )⧹TiN, when the working atmosphere for the Ti(C x N 1−x ) layer was C 2 H 2 ⧹N 2 = 75%⧹25%. The minimum of the sliding-wear-resistance (durability indicator γ 60 = 10×10 [3][mm −3]) occurred when the working atmosphere for the Ti(C x N 1−x ) was C 2H 2⧹N 2 = 50%⧹50%.

Growing multilayer gradient thin films via in situ neurocomputing

Multiple-layer thin films of less than 2 μm are presently typically deposited via mechanical manipulation of substrates. Interlayer gradients are typically accomplished by the rotation of substrates between two or more material deposition sources. Film deposition rates are often maintained with limited instrumentation, and no feedback control. Additionally, most tribological hard films deposited on relatively soft substrates need to be deposited with a buffer or interface layer in order to bond a particular film to a substrate. Often, this buffer layer is deposited by manually ramping rotation speeds or source deposition rates, increasing film variability. This research is focused on identifying and relating observed process characteristics to the resulting material chemistry and structure, with a goal of dynamically controlling the material characteristics for multilayer films using in situ neurocomputing. Of specific interest is the ability to grow multilayer diamond-like carbon (DLC)-ceramic–metal films. DLC films deposited by pulsed laser deposition (PLD), combined with the reactive gas DC magnetron deposition of titanium to create Ti–TiN–DLC or Ti–TiC–DLC material gradients will be the focus of this work. In situ laser-induced florescence (LIF) spectroscopy and a quartz crystal microbalance are used for in situ plume sensing with the aim of controlling the film deposition rates and the resulting deposited structure.

Investigation into three-dimensional laser processing of tribological coatings

Tribological coating design has evolved from single layer/single phase to multilayer and composite architectures. The early single-layer coatings were not efficient for arresting cracks, distributing loads, relaxing stress, and preventing adhesive failures. Second-generation coatings with multilayer, gradient, and composite architectures added another dimension to the coating design and allowed much better accommodation of stresses and crack arresting. This paper considers the further evolution of coating design to three dimensions, where the lateral property variation was added to the cross-thickness property variation. The three-dimensional design considerably improved the tribological characteristics of hard coatings, by permitting solid lubricant replenishment inside the friction contacts. A functionally gradient Ti–TiC–TiC/diamond-like carbon coating with an upper layer of a tough nanocrystalline/amorphous composite was used for load support, crack prevention, and stress equalization. This coating was processed with laser irradiation to form grooved tracks along wear paths, which were then filled with MoS 2. This provided a solid lubricant reservoir in the lateral dimension of the coating. The three-dimensional coating was tested in long-duration sliding tests at fixed and cycling humidity. The coating exhibited environmental adaptation with friction coefficients of 0.15 in humid air and 0.02 in dry nitrogen. The wear life was increased by at least one order of magnitude in comparison to that for a hard gradient coating with a top layer of MoS 2 without any three-dimensional laser processing. Discussions of three-dimensional coating tribological properties, friction and wear mechanisms are provided. The environmental adaptation achieved with three-dimensional coating processing can be beneficial for aerospace applications.

Design of a Ti/TiC/DLC functionally gradient coating based on studies of structural transitions in Ti–C thin films

Development of optimized hard coatings requires a multilayer, functionally gradient approach, where adhesion, load support and low friction regions must be elements of the design architecture. Each of these functional regions should be joined through appropriate transition regions to reach desired coating performance. The design of coatings with hard and lubricious diamond-like carbon (DLC) surfaces requires a study of transitions between adhesive metal, load supporting carbide, and wear-resistant DLC materials. These transitions were investigated on the Ti–C system prepared by a hybrid of magnetron sputtering and pulsed laser deposition. Crystalline α-Ti, TiC and amorphous DLC films were formed at 100 °C substrate temperature by varying film chemical composition. Phase transitions between Ti–TiC–DLC were analyzed with XPS, XRD and Raman spectroscopy. A gradual replacement of hcp α-Ti with fcc TiC, and a two-phase region consisting of crystalline TiC and amorphous carbon (a-C) in transitions from Ti to TiC and from TiC to DLC were found. These transitions were reflected in mechanical properties investigated with nanoindentation. A hardness maximum in the two-phase TiC/a-C region was found. The resulting composition-property maps were used to design a wear-resistant coating with Ti/TiC/DLC transitions and a gradual increase in hardness from a steel substrate to a super-hard (60–70 GPa) self-lubricating DLC layer on the surface. This provided a hard coating with a low friction surface, which also resisted brittle failure in tests with high contact loads. © 1997 Elsevier Science S.A. All rights reserved.

High temperature activation energy for plastic deformation of titanium carbide single crystals as a function of the C : Ti atom ratio

By applying the theoretical model of Mohamed and Langdon [1] the activation energy for high temperature plastic deformation of TiCx single crystals as a function of C : Ti atom ratios is obtained. It is found that the values for the activation energy at the critical resolved shear stress are lower than the lattice self-diffusion data for carbon, except for x=0.75. At this concentration a peak in the activation energy, 560 KJ, mol-1, which is about 75% of that for lattice self-diffusion of Ti in TiC, appears. This situation is due to an ordering hardening caused by a contraction of the “window”, formed by titanium atoms, through which the carbon atom diffuses. It is concluded that the x-dependence of the activation energy can be understood by considering that during deformation the diffusion processes of carbon and titanium atoms are coupled.

メカニカルアロイング法により作製したＴｉＣ粒子強化チタンの機械的性質

Ti powder and TiC particles were blended by two methods of simple blending and mechanical alloying. Hot pressing was applied after the blending and mechanical properties of these Ti base composites with 0 to 20 mass % TiC were studied. Tensile strength of the simply blended composite showed a peak at 5 mass % TiC and it decreased by further adding of TiC. On the other hand, tensile strength of the mechanically alloyed composite increased with the content even above 5 mass % of TiC. Sharp decrease in elongation occurred at 3 mass % TiC, and elongation of the mechanically alloyed composite was always slightly larger than that of the simply blended composite. Young's modulus of the composite increased linearly with TiC content along with a rule of mixture. Debonding at the matrix/particle interface did not occur during tensile deformation, but relatively large TiC particles were observed to be cracked easily. Mechanical alloying is a useful method for the strengthening of Ti base composites with TiC particles, as the structure having small TiC particles of uniform dispersion is made by this method.

Multilayer films of TiC, Ti and Cu for the gravity probe B relativity mission gyroscopes

Single-component and multilayer films of TiC, Ti and Cu have been produced by sputtering on fused quartz substrates and have been investigated for suitability as electrodes for the electrostatically suspended gyroscopes of Gravity Probe B. The main requirements for these films are low electron field emission in fields of 3 x 10 7 V m −1, low film stress, and good thermal and electrical conductivity in the temperature range 2 K–400 K. The films have been studied using X-ray diffraction, scanning electron microscopy (SEM), Auger electron spectroscopy, Rutherford backscattering spectrometry, and four-point resistivity techniques. SEM measurements indicate that the TiC films have very smooth surfaces and that multilayer films of TiC, Ti and Cu have reduced roughness as compared with the Ti-Cu multilayer films. Seven-layer 2.5 μm thick Ti-Cu films have been successfully used in the Gravity Probe B gyroscopes, meeting all requirements. Multilayer films of TiC Ti and Cu are at present being tested with the expectation that they will further improve gyroscope performance.

Multilayer films of TiC, Ti and Cu for the Gravity Probe B Relativity Mission gyroscopes

Single-component and multilayer films of TiC, Ti and Cu have been produced by sputtering on fused quartz substrates and have been investigated for suitability as electrodes for the electrostatically suspended gyroscopes of Gravity Probe B. The main requirements for these films are low electron field emission in fields of 3 x 107 V m−1, low film stress, and good thermal and electrical conductivity in the temperature range 2 K–400 K. The films have been studied using X-ray diffraction, scanning electron microscopy (SEM), Auger electron spectroscopy, Rutherford backscattering spectrometry, and four-point resistivity techniques. SEM measurements indicate that the TiC films have very smooth surfaces and that multilayer films of TiC, Ti and Cu have reduced roughness as compared with the Ti-Cu multilayer films. Seven-layer 2.5 μm thick Ti-Cu films have been successfully used in the Gravity Probe B gyroscopes, meeting all requirements. Multilayer films of TiC Ti and Cu are at present being tested with the expectation that they will further improve gyroscope performance.

Reaction Milling of Metals with Hydrocarbon or Ceramics (<I>Overview</I>)

Recent results on reaction milling have been reviewed focusing on metal-hydrocarbon and metal-ceramics systems. An intermediate metastable phase during the reaction was first revealed with Ti-heptane system. It was shown that stacking faults in Ti introduced by milling is stabilized by C and H which are decomposition products of heptane. Formation of a metastable Ni3C which has a positive heat of formation was revealed at the milling of Ni with SiC. An incubation period for the reaction was observed and related to a threshold value of the stored energy during milling as the driving force of the reaction. The reaction milling of Ti–Al-heptane and Ti–Si3N4, Ti–SiC systems followed by hot consolidation could produce fine composites of TiAl–Ti4Al2C2, TiN–Ti silicides and TiC–Ti silicides. The phases present in the compacts were altered with the process parameters. A kinematical model for the preference of the phases was presented. Improved sinterbility and superplastic-like ductility at elevated temperatures have been demonstrated.

Crystalline potential for photoelectron scattering phase-shift calculations and X-ray absorption spectra of Ti in crystals

X-ray absorption spectra (XAS) of Ti in crystals of Ti metal, TiC, TiN and TiO2 rutile are calculated in EXAFS and XANES regions. Single, double and triple photoelectron scattering processes are included through the spherical-wave formalism and the crystalline muffin-tin (MT) potential model, which employs a Hartree-Fock exchange interaction between photoelectron and core electrons inside MT spheres. Overall agreement of the theoretical and experimental spectra is obtained on the absolute photon energy scale. This result enables one to treat the experimental XAFS without using adjustable parameter E0. The neutral-atoms approximation is shown to be adequate for the phase-shift calculations in XAS theory for both metals and insulators. A comparison of Ti K XAFS of Ti metal calculated by means of various exchange-correlation potentials for the photoelectrons inside MT spheres is carried out. The best results are shown to be provided by Hartree-Fock and Dirac-Hara exchange potentials.

ＴｉＮ被覆したステンレス鋼の硫酸水溶液での耐食性

TiN films were deposited under various conditions onto SUS304 stainless steel substrates by a hollow cathode discharge (HCD) type ion plating process. The corrosion resistance of the TiN-coated specimens in the active region was estimated in aqueous solutions of sulfuric acid, mainly by an electrochemical method. Measurements of the anodic polarization curves showed that the critical current density for passivation of the TiN-coated specimens was smaller than that for specimens without a TiN coating, that is, that active dissolution was retarded by TiN coating. The cathodic reaction tended to be similarly retarded by TiN coating. The corrosion resistance of the TiN-coated specimens was further improved by Ti undercoating and TiC coating under the TiN coating layer. This is attributed to the fact that the Ti undercoating and TiC coating decreased the number of defects that penetrate through the coating layers to the stainless steel substrate, that is, increased the intercepting effect of the coating layers from its surroundings. The intercepting effect of the coating layer from the surroundings of the specimens treated at 300°C was superior to that of the specimens treated at 450°C. The effect of hydrogen on the crack morphology of the TiN films was remarkable, and in the case of TiN films put into a hydrogen surroundings, cleavage fractures occurred.

Étude des bandes de precipitation dans le carbure de titane sous stoechiométrique

In the course of the study of the TiC system, precipitation bands have been found in the TiTiC double phase up to the composition TiC 0·52. Similar bands have also been found in the systems VC, NbC, TaC and HfC. Metallographie observation, potentiostatic etching analysis and electron microprobe as well as electron diffraction have shown that these precipitates are α titanium. The presence of these bands modify several properties of the carbide phase such as microhardness and bending tests results; the intrinsic value of the microhardness is diminished and the bending tests give rise to slip bands along the boundary of the precipitates. Thin foil electron microscopy permitted an orientation determination of the precipitates: (III) TiC ∥ (0001) Ti with 〈110〉 TiC ∥ 〈112̄0〉 Ti. The electron diffraction diagrams revealed also the presence of twins as well as an ordered phase in the matrix (doubling of certain lattice spacings).