Titanium Carbide Coatings Research Articles

Fabrication and oxidation resistance of titanium carbide-coated carbon fibres by reacting titanium hydride with carbon fibres in molten salts

Using carbon fibres and titanium hydride as a reactive carbon source and a metal source, respectively, a protective titanium carbide (TiC) coating was formed on carbon fibres in molten salts, composed of LiCl–KCl–KF, at 750–950 °C. The structure and morphology of the TiC coatings were characterised by X-ray diffraction and scanning electron microscopy, respectively. The oxidation resistance of the TiC-coated carbon fibres was measured by thermogravimetric analysis. The results reveal that control of the coating thickness is very important for improvement of the oxidation resistance of TiC-coated carbon fibres. The oxidative weight loss initiation temperature for the TiC-coated carbon fibres increases significantly when an appropriate coating thickness is used. However, thicker coatings lead to a decrease of the carbon fibres' weight loss initiation temperature due to the formation of cracks in the coating. The TiC coating thickness on carbon fibres can be controlled by adjusting the reaction temperature and time of the molten salt synthesis.

Comparative performance of nanocomposite coatings of TiC or TiN dispersed in a-C matrixes

Titanium carbide (TiC) and nitride (TiN) are two of the most used materials in the field of protective coatings, due to their optimal mechanical and tribological properties. The addition of the second phase can provide extra benefits to the coating, like improved hardness, reduced friction and/or oxidation resistance. In this work, we present two series of coatings in which hard crystalline TiC and TiN phases are mixed at the nanometric level with a soft lubricant phase like amorphous carbon (a-C). Both series of TiC/a-C and TiN/a-C nanocomposite coatings were prepared by double magnetron sputtering of C and Ti(N) targets in a Ar atmosphere ( P = 5 × 10 − 3 Torr) by changing the power ratio applied to each magnetron. The chemical composition has been measured by electron energy loss spectroscopy, and the phase composition changes gradually from pure C to pure TiC or TiN through nanocomposite structures with variable phase contents. These structures are confirmed by transmission electron microscopy and diffraction techniques, like X-ray diffraction and electron diffraction. The mechanical and tribological properties are found to be mainly controlled by the hard/soft phase ratio present in the coating. The changes in hardness values follow similar trends in both types of nanocomposite samples. Introducing a small amount of TiN or TiC into a-C matrix causes a hardness reduction, but further addition of crystalline phase makes increase the hardness. The best tribological properties are found for nanocomposite coatings (both TiN/a-C and TiC/a-C) with high amount of a-C (> 65%), showing low friction values ( f ∼ 0.1) and high wear resistance ( k about 10 − 7 mm 3 N − 1 m − 1 ). However, coatings with 50–60% a-C show a good compromise between tribological and mechanical properties.

Effects of Hydrogen Ion Implantation on TiC-C Coating of Stainless Steel

Titanium carbide coatings are widely used as various wear-resistant material. The hydrogen erosion resistance of TiC-C films and the effect of hydrogen participation on TiC-C films were studied. Seventy-five percent TiC-C films are prepared on stainless steel surface by using ion mixing, where TiC-C films are deposited by rf magnetron sputtering followed by argon ion bombardment. The samples are then submitted to hydrogen ion implantation at 1.2 × 10 −3 Pa. Characterization for the 75% TiC-C films was done with SIMS, XRD, AES, and XPS. Secondary ion mass spectroscopy (SIMS) was used to analyze hydrogen concentration variation with depth, X-Ray diffraction (XRD) was used to identify the phases, and Auger electron spectra (AES) as well as X-ray photoelectron spectra (XPS) were used to check the effects of hydrogen on shifts of chemical bonding states of C and Ti in the TiC-C films. It is found that TiC-C films on stainless steel surface can prevent hydrogen from entering stainless steel.

Low‐Temperature Preparation of Titanium Carbide Coatings on Graphite Flakes from Molten Salts

Titanium carbide (TiC)‐coated graphite for refractory castable applications was prepared via reacting titanium metal powder (∼45 μm) and natural graphite flakes (100–300 μm) for 5 h at 950°C in a KCl‐based salt in Ar atmosphere. TiC coatings formed on graphite flakes were uniform, crack‐free, and composed of nanosized particles (20–40 nm). The “template‐growth” mechanism played a dominant role in the coating formation process.

Preparation of a titanium carbide coating on carbon fibre using a molten salt method

A method for preparing protective titanium carbide (TiC) coatings on carbon fibres has been developed using a molten salt synthesis method. The TiC coatings were formed on the surface of carbon fibres in a reaction medium consisting of Ti powder in a mixture of molten LiCl–KCl–KF salts under an argon atmosphere at 900 and 950 °C. The structure and morphology of the TiC coatings were characterized by XRD, SEM and energy dispersive X-ray (EDX) analyses. The coatings consisted of homogeneous single phase cubic TiC with thicknesses in the range of 60–800 nm. Variation of the synthesis time and reaction mixture was found to significantly affect the thickness and integrity of the TiC coating although variation of the reaction temperature had little effect. The coating thickness was closely related to the composition of the molten salts and to the molar ratio between the carbon fibre and titanium.

The chemistry, morphology, topography of titanium carbide modified carbon fibers

Titanium carbide coatings were successfully applied on carbon fibers using reactive chemical vapor deposition approach. Chemistry, morphology, and topography of the TiC modified carbon fibers have been studied by scanning electron microscopy/energy dispersive spectroscopy, atomic force microscopy, and X-ray diffraction analysis. Uniform, adherent, crack-free and non-bridging coatings were obtained. After application of the TiC coating on carbon fibers, relief becomes more smooth and uniform. This is confirmed by decrease of the roughness parameter and the average height value of relief, as well as by decrease of scatter of measured heights. The coating consists of radially oriented crystals with high aspect ratio. Crystals are aligned in rows which are parallel to fiber axis. An increase in the tensile strength has been achieved by introducing the TiC coating on carbon fiber, the average strength and the Weibull modulus parameters were 2.55 GPa and 4.36 GPa, respectively. The obtained results can be useful for the predictive design of the well-matched interphase zone for composite materials reinforced by the TiC-coated carbon fibers.

State of residual stress in laser-deposited ceramic composite coatings on aluminum alloys

The nature and magnitude of the residual stresses within laser-deposited titanium carbide (TiC) coatings on 2024 and 6061 aluminum (Al) alloys were investigated. Macro- and micro-stresses within the coatings were determined using an X-ray diffraction method. Owing to increased debonding between the coating and the substrate, the macro-stresses were found to be compressive and to decrease in magnitude with increasing processing speed. The origin of the macro- and micro-stresses is discussed. To that end, transmission electron microscopy observations showed no evidence of plastic deformation within selected coatings. The micro-stresses in the TiC particulate and aluminum matrix phases within the coatings were found to be independent of the amount of debonding. This study could assist in optimizing the processing parameters to fabricate composite coatings for specific applications.

Pulsed electrode deposition of superhard coatings on steel substrates: microstructural and chemical study

Titanium carbide (TiC) coatings have been deposited on steel using the pulsed electrode deposition (PES) technique. Different experimental parametric conditions were used in the deposition process. Microstructural and chemical characterisations of the coatings were performed using electron microscopy and X-ray diffraction techniques. Pulsed electrode technique produced hard coatings, which are commonly defect and crack free. Small TiC and Fe3C particles were randomly distributed in a Fe matrix without any preferred crystallographic orientation. The relationships between the microstructural properties and the deposition processing conditions were also explored.

Titanium carbide films obtained by conversion of sputtered titanium on high carbon steel

One the most important limitations to the industrial use of hard coatings in severe conditions is associated with their limited adhesion to the substrate. A number of research works have been done in various directions in order to improve the adhesion by post treatments such as laser remelting or thermal treatments. The aim of this work is to evaluate the possibility of using the substrate itself as a carbon source, in order to create very adherent hard titanium carbide coatings by means of a diffusion/precipitation process. A film of pure titanium was prepared by magnetron sputtering on a high carbon content steel substrate. Coated samples were then annealed in vacuum for 1 h at temperature ranging from 500 to 1100 °C. It was observed that the film was totally, partially or not transformed into titanium carbide, depending on heat treatment temperature. The transformation of titanium layer in titanium carbide takes place firstly at the interface between the film and the substrate, then it expands through the whole film thickness, toward the outer surface, by diffusion of carbon coming from the substrate. As a result, complete conversion of the titanium film in titanium carbide is obtained when an annealing temperature of 1100 °C is used. A higher adhesion, measured by means of a scratch tester, is found for this coating if compared to the one obtained on samples treated at lower temperatures and to other literature data on coatings having similar thickness and composition.

Theoretical quest for the titanium-substituted hydrocarbons

Using theoretical calculations we predict a novel family of compounds, which might serve for hydrogen storage, and for chemical vapour deposition of titanium carbide coatings.

Deposition of Protective Coatings on Tungsten-Free Hard Alloys

The process of deposition of coatings of titanium carbide, vanadium carbide, and chromium carbide on the surface of the tungsten-free hard alloys TN20, KNT16, and KKhN15 is investigated. The structure and phase composition of specially created layers are explored and the microhardness measured (11.5-24.5 GPa). The optimal temperature-time conditions for deposition of carbide coatings is determined. The ultimate transverse bending strength of hard alloys with and without coatings is determined. From the results of industrial tests, a two- to five-fold increase in the durability of plates in cutting was noted.

Hybrid pulsed laser deposition and Si-surface-micromachining process for integrated TiC coatings in moving MEMS

Titanium carbide (TiC) is one of the preferred coatings for improving the performance of macroscopic moving mechanical components due to its established wear-resistance. Pulsed laser deposition (PLD) is an excellent method for depositing TiC, because unlike any other deposition process for TiC, PLD offers the capability of producing high-quality films even at room temperature. Using a modified PLD technique, especially designed for the deposition of particulate-free films, TiC coatings have been deposited at room temperature on silicon (Si) and on several types of thin films typically employed for fabricating microelectromechanical systems (MEMS). Our results demonstrate that TiC coatings also offer a high wear-resistance to Si surfaces, which in turn has led to our application of TiC to “moving” Si MEMS devices. The performance of moving Si MEMS devices is limited by their poor operational lifetimes, which have been attributed to the excessive wear at sliding Si interfaces. The work presented here describes a hybrid process, whereby PLD is used in conjunction with a user-friendly Si surface micromachining scheme for inserting wear-resistant TiC coatings between critical sliding Si interfaces in MEMS devices. This paper describes the properties of PLD-TiC for MEMS and the hybrid PLD-surface micromachining process for the integration of TiC coatings into Si MEMS.

Integrated TiC coatings for moving MEMS

The application of wear-resistant coatings to microelectromechanical systems (MEMS) devices offers the potential of addressing the reliability of moving MEMS devices. However, coating non-line-of-sight, concealed surfaces in fully released 3D MEMS structures, especially those behind micron-sized apertures, is a difficult problem to overcome with most deposition techniques. A practical and viable solution to this problem is the direct integration of wear-resistant coatings into the MEMS fabrication process. Using this approach we have inserted pulsed-laser-deposited titanium carbide (TiC) coatings between critical polysilicon interfaces during fabrication of a MEMS device. This paper describes the details of inserting laser-ablated TiC coatings into a user-friendly surface micromachining process for MEMS to protect key sliding Si surfaces in MEMS motors. This hybrid technology is an effective way of inserting wear-resistant coatings such as TiC into the MEMS fabrication scheme.

Synthesis of titanium carbide/chromium carbide multilayers by the co-evaporation of multiple ingots by electron beam physical vapor deposition

Titanium carbide and chromium carbide multilayer coatings with varying individual layer thicknesses were synthesized by the co-evaporation of titanium, chromium, and carbon (through tungsten) ingots by electron beam-physical vapor deposition. The adhesion of the multilayer coatings was found to be greater than 50 N. The hardness of the titanium carbide/chromium carbide multilayer coatings was found to increase from 1302 VHN 0.050 to 2052 VHN 0.050 by decreasing the thickness of the individual layer from 1.2 to 0.1 μm. In addition, the average grain diameter was also found to decrease from 3.315 to 0.356 μm by decreasing the thickness of the individual layers. The fracture toughness of the TiC/CrC multilayer coatings decreased from 4.179 to 1.411 MPa-m 1 2 with decreasing layer thickness. Lastly, the amount of compressive stress in both the TiC and CrC layers within the multilayer coating was found to decrease with decreasing individual layer thickness. The samples were characterized by various techniques including Vicker's hardness, X-ray diffraction, scanning electron microscopy, scratch testing and fracture toughness, with the results being presented.

Laser chemical vapor deposition of TiC on tantalum

Laser chemical vapor deposition (LCVD) of titanium carbide (TiC) coatings onto tantalum substrates using hydrogen gas, titanium tetrachloride (TiCl4) and either methane (CH4) or acetylene (C2H2) source gasses was investigated. The influences of the molar ratio of the source gases and the deposition temperature on the phase assemblage, composition, and morphology of the coatings was examined. Using C2H2, nearly stoichiometric coatings were produced at 1000°C and at a TiCl4/C2H2 ratio of 1/0.4. Stoichiometric coatings were also produced using CH4 but the deposition temperature was 400°C higher and a much larger fraction of the carbon source was required compared to C2H2. Although deposition rates were much slower when using CH4, the coatings exhibited a smoother surface finish and had a higher density compared to those produced using C2H2. The suitability of CH4 and C2H2 as carbon sources for depositing stoichiometric, phase-pure coatings is discussed in light of these results.

Microstructure of Pulsed-Laser Deposited Titanium Carbide Thin Films Grown for Tribological Applications

The carbides and nitrides of transition metals, are excellent candidates for hard coatings for tribological applications. Recently a novel pulsed laser deposition (PLD) technique has been developed for the room temperature growth of particulate free titanium carbide (TiC) coatings on bearing steels. On a completely different scale from ball bearing applications, moving microelectricalmechanical systems (MEMS) face issues of limited lifetime as a result of rapid wear of the silicon components. The integration of hard tribological coatings into moving MEMS structures should greatly increase the functional lifetime of these devices. The same PLD technique has been used to deposit TiC thin film onto MEMS test structures consisting of multilayer coatings on Si substrates, and patterned 3-D Si substrates. This procedure for growing TiC appears to be compatible with conventional MEMS fabrication procedures.

Keimbildung und Schicht-Wachstum beim Titanieren von Schnellarbeitsstahl / Nucleation and Coating Growth in the Titanising of High Speed Steels

In order to increase their resistance to wear and corrosion, high speed steels are often hard faced with titanium based coatings. In the work discussed in this article, such coatings are produced by a process of thermo-chemical diffusion known as titanising. The nucleation and growth mechanisms of the coatings produced using this process are investigated. In the investigation the process parameters of coating time and temperature are varied, and the titanium carbide coatings produced examined and characterised in respect of their morphology, chemical composition and crystallographic structure. The nucleation and growth of the coatings are affected by each of the two components of the substrate, these being the primary carbides and the matrix containing dissolved carbon. The formation of the coating starts with the matrix on which the nuclei form, which then proceed to cover the whole of the surface of the metal by a process of lateral growth. The temperature of the process has a considerable effect on both the nucleation process and growth of the coating, an increase in the processing temperature resulting in a reduction in the nucleation density. The coatings exhibit a morphology made up of fine columnar crystals and grains. The chemical composition of the coatings is largely dependent on the parameters investigated. With short treatment times Ti(C,N)-coatings are obtained, whilst with longer coating times combined with higher process temperatures, TiC-coatings are formed.

Titanium carbide coatings deposited by reactive ion beam-assisted, electron beam–physical vapor deposition

Titanium carbide (TiC), in addition to other transition metal carbides, has excellent wear-resistant properties in machining of stainless and high speed tool steels. TiC was successfully deposited on 304 stainless steel by reactive ion beam-assisted electron beam–physical vapor deposition (RIBA, EB–PVD). The hardness values ranged from 1100 to 3500 VHN 0.050 depending on the processing parameters. The surface morphology and degree of texturing were correlated with the processing conditions. Ion bombardment resulted in strong surface and growth texture in primarily the (111) orientation. A change from the (111) orientation to the (200) was observed at high substrate temperatures. Vickers hardness, scanning electron microscopy (SEM), X-ray diffraction (XRD) and electron probe microanalysis (EPMA) were used to characterize these films.

Integration of wear-resistant titanium carbide coatings into MEMS fabrication processes

Microelectromechanical systems (MEMS) are a key technology for small-scale satellites, integrated sensors, and intelligent control systems. However, a major limitation for Si-based systems involving tribological components is their inability to withstand prolonged sliding surface contact that results in high wear and causes them to fail within minutes of operation. Our aim is to protect the Si surfaces with wear-resistant coatings. Due to practical limitations of coating fully released MEMS structures, we have addressed the integration of the coating into the MEMS processing sequence. This paper describes the direct integration of a pulsed-laser-deposited wear-resistant titanium carbide (TiC) coating into the Si MEMS fabrication process. The in situ deposited TiC layer also provides an ideal substrate to the various possible lubrication schemes proposed for moving MEMS.

Pulsed-laser deposition of particulate-free TiC coatings for tribological applications

Hybrid bearings comprising ceramic or ceramic-coated steel balls and steel raceways can provide good fatigue life and resistance to wear. One of the coating materials that has received serious consideration in hybrid systems is titanium carbide (TiC). At present, the commercially available process for the deposition of TiC involves the heating of steel substrates to fairly high temperatures (>900 °C). The high-temperature process involves considerable costs and complexities that are associated with the post-deposition heat treatment and repolishing of the coated steels for bearing applications. Pulsed-laser deposition (PLD) is ideally suited to deposit TiC coatings on bearing steels at room temperature. However, it is well known that codeposition of particulates has been one of the most challenging problems of PLD. This is especially of concern when dealing with hard coatings for tribological applications. Here we describe a novel and extremely simple method of depositing high-quality, particulate-free TiC coatings on bearing steel surfaces that uses PLD. The method relies on a new non-line-of-sight deposition that uses a permanent magnet and prevents particulates from arriving at the substrate. The surface roughness of TiC films deposited on steels by way of this technique has an extremely low root mean square value of 1.6 nm. The TiC films have been extensively characterized for their morphology, chemical composition, and mechanical properties with scanning electron and atomic force microscopy, X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and nanoindentation. Time-resolved emission has been used for the in situ characterization of the laser-ablated TiC plume and has resulted in the identification of various plume species as a function of laser parameters. The spectroscopic results are correlated to film growth and to our modified PLD method.