TiC Coatings Research Articles

DLC multilayer coatings for wear protection

Abstract Amorphous hydrogenated diamond-like carbon (DLC) coatings containing a small amount of titanium have been deposited onto AISI 420 steel substrates by unbalanced magnetron sputtering. In order to make the diamond-like carbon coating adhere to the metal, four kinds of graded interlayers, i.e. Ti, TiN, TiCN and TiC, have been used, taking advantage of the fact that the Ti layer adheres to the metal and DLC adheres to the TiC layer. The total thickness of the DLC coatings is 2.0 μm. The DLC coatings showed excellent properties, i.e. high microhardness values (higher than 39 Hv (GPa)), excellent adhesion (Lc 10.0–11.0 kg), friction coefficients against an A1 2 O 3 ceramic ball being in the range 0.08–0.3 and an extremely long wear lifetime. In addition, wear tracks of the DLC coatings as well as wear scars of the sliding A1 2 O 3 balls were investigated with the help of optical microscopy and scanning electron microscopy studies. Tribological studies of the DLC coatings with other ball wear materials were also carried out. The results indicate that the studied DLC coatings posses dramatically improved wear protection properties as compared to e.g. high-quality TiN or TiC coatings. The coatings were analysed using X-ray diffraction, infrared spectroscopy, Rutherford backscattering spectrometry and elastic recoil detection.

Growth and structure of TiC coatings chemically vapour deposited on graphite substrates

TiCxNy coatings were grown on graphite substrates in a computer-controlled, hot-wall chemical vapour deposition (CVD) reactor, using gas mixtures of TiCl4–CH4–N2–H2 at a total pressure of 10.7 kPa (80 torr) and at a temperature of 1400 K. Growth rate, composition, morphology and crystallographic texture of the TiCxNy coatings were investigated as a function of the CH4/CH4+N2 ratio in the range 0–1 at a constant CH4+N2 flow rate of 370 standard cubic centimeters per minute (sccm). The C/C+N ratio and growth rate of the TiCxNy coatings increased with increasing CH4/CH4+N2 ratio in the gas phase. The compositions of the coatings with C/C+N ratios in the range 0–1 were found to be between the thermodynamic and the kinetic predictions. Morphology and preferred orientation of the coatings were observed to be strongly affected by the CH4/CH4+N2 ratio in the gas phase.

An XPS Study of the Chemical Interactions of the Extreme Pressure Lubricant Additive Lead Naphthenate with Titanium and Titanium Compound Surfaces

The surface chemical interactions between boundary or extreme pressure (EP) lubricant additives and the mechanical components they protect often determine the performance and life of marginally lubricated and highly loaded mechanisms. Most of these additives have been developed for use with steel components, and a lack of fundamental understanding regarding the surface bonding and reactivity occurring in the mechanical contact severely limits the application of these additives to mechanisms incorporating new materials. This work examines the chemical interactions between the EP additive lead naphthenate (Pbnp) and a series of titanium-based materials (Ti, TiB{sub 2}, TiC, TiN, and TiO{sub 2}). These X-ray photoelectron spectroscopy (XPS) studies show that Pbnp applied via solution chemisorbs to all of these materials and that the surface activity is enhanced by damaging the substrate (i.e., wear) during exposure. In addition, both Ti and TiB{sub 2} are capable of chemically reducing Pbnp to metallic lead, while TiO{sub 2} stabilizes and oxidized form of lead. Neither TiC nor TiN, the most widely used of these materials for antiwear coatings, is capable of chemically reducing Pbnp or of retaining significant amounts of Pbnp fragments at elevated temperature. The results indicate that Pbnp is probably not a good candidate asmore » an EP additive for TiC and TiN coatings. 33 refs., 17 figs., 4 tabs.« less

Influence of carbide coatings on the oxidation behavior of carbon fibers

The oxidation behavior of reactive carbon fibers, such as ex-Pan T300, is studied in oxidizing environments by means of TGA and tensile strength measurements. Different carbide coatings are investigated with a view to fiber protection during an air exposition at high temperature. Thin, continuous, and uniform films of TiC, SiC, B 4C, or B 4C SiC multilayers are obtained by an RCVD process. Complementary experiments are performed on bulk graphite substrates coated by the same process. The carbide thicknesses do not exceed 60 nm for the T300 fibers and 60 μm for the bulk substrates. The presence of such coatings is found able to protect the carbonaceous materials against oxygen and air oxidation for extended periods to temperatures of at least 600 °C. However, SiC and TiC coatings that form silica and rutile films during oxidation offer only limited protection due to the diffusion of oxygen along microcracks and grain boundaries of the oxides. B 4C and B 4C SiC multilayers give better protection both in a dry oxygen atmosphere and in room air. Boron oxide and borosilicate have a glassy structure, and they act as a diffusion barrier, providing protection by inhibition of oxygen diffusion, thereby slowing down the carbon gasification. The mechanical characteristics of the fibers protected by a boron-silicon carbide coating remain constant after a half hour of oxidation at 600 °C.

On Superstoichiometric Ti-C, Si-C and Ta-C PVD Coatings

AbstractDifferent PVD coatings are used to reduce the wear of tools and other machine parts, and to improve their service life [1]. During the last years, a number of developments have been made in the field of carbon coatings. These coatings show a low friction coefficient, e.g. against steel, and therefore have a high potential in decreasing the friction and wear of coatings in tribological applications. This PVD process can be stabilised by using a metallic target which is vaporised in a carbon and hydrogen atmosphere. The carbon rich side of the metal/carbon system is object of this study. Slightly superstoichiometric coatings in the range of 50–60% carbon content have very good friction properties too and with the potential to better film properties (coating adhesion due to internal stress, microhardness). In this paper the mechanical properties of coatings in the systems Ti-C, Si-C and Ta-C are described and the different microstructures are discussed.

Tribological behavior of TiN, TiC xN y and TiC coatings prepared by unbalanced magnetron sputtering techniques

TiN, TiC and TiC x N y (0< x<1, 0< y<1) coatings were deposited onto AISI 420 substrates by unbalanced magnetron sputtering techniques at the substrate temperature of 350°C. The structures of all coatings were examined by X-ray diffraction and Rutherford backscattering spectrometry. TiN and TiC x N y coatings exhibit a strong (111) or (200) preferred orientation. TiC coating exhibits a (220) preferred orientation. The hardness values for all the coatings increase with the carbon content varying between pure TiN and pure TiC coating. The different tribological behavior of TiN, TiC and TiC x N y coatings were investigated and compared. The amount of surface wear was evaluated by optical and scanning electron microscopy. The results of the wear tests show that friction coefficients are in the range 0.17–0.3 for all coatings. The wear lifetimes of the TiC x N y coatings with different carbon concentrations increase with the carbon content from 11 to 32 h. Relative soft TiN coatings exhibit a short wear lifetime, about 3.5 h. In general, the wear behaviors of TiC x N y coatings with high carbon content are superior to those of either TiN or TiC coating.

The CVD of Ceramic Protective Coatings on SiC Monofilaments for Use in Titanium Based Composites

Abstract TiB2, TiC and TiN protective coatings have been deposited onto SiC monofilament fibers by the CVD technique using a cold-wall reactor at reduced pressure. The effect of deposition conditions on the morphology, microstructure, phase composition and adherence of the coatings were studied. The physical and chemical compatibility of these ceramic coatings with SiC filaments together with titanium-alloy matrices were assessed and compared. Dense and uniform TiB2 coatings have been deposited successfully onto SiC monofilaments. The coating is stable on the SiC fiber and acts as an effective: barrier against the vigorous SiC/Ti-6Al-4V interfacial reaction. The adhesion of TiC on SiC fibers is comparatively weaker than the TiB2 coating. There was no significant reaction found at the interface of TiC/Ti except at the interface of TiC/SiC. Examination of the TiN coatings showed severe cracking and spalling, hence TiN could not provide protection in a Ti-alloy matrix.

Properties of TiCN coatings prepared by magnetron sputtering

TiCN coatings were deposited onto AISI 420 substrates by a magnetron sputtering technique using a reactive gaseous mixture of methane and nitrogen. The structure and composition of the coatings have been analyzed by x-ray diffraction and Rutherford backscattering spectrometry. In addition, the microhardness, friction coefficient, and wear behavior of the coatings were also measured. The influence of deposition parameters on the characteristics of the coatings has been investigated. The experimental results show that the TiCN coatings exhibit a strong (111) or (200) preferred orientation. The maximum hardness of the coating is about 3648 kg mm−2. Adhesion of the coating is excellent. The maximum scratch test critical load is about 8.2 kg. The characteristics of wear resistance for the TiCN coatings are also excellent in comparison with either pure TiN or TiC coatings.

Formation of TiC coatings on steels by a fluidized bed chemical vapour deposition process

The use of a fluidized bed process for the production of hard wear- and corrosion-resistant coatings of carbides, nitrides and carbonitrides of cementing metals is promising since it can lead to a flexible surface treatment technology combining adaptability with relatively low capital and operational costs. In this paper the feasibility of a fluidized bed process for the formation of titanium carbide coatings using chemical-vapour-deposition-based reactions is discussed. The method involves a treating agent consisting of a powder mixture of Al 2O 3 with FeTi which is fluidized at elevated temperature with Ar. As an activator of the process NH 4Cl was used. The use of explosive hydrogen is avoided by the formation of the vapours of the materials to be coated in situ in the reactor. With this method, adherent and dense coatings of TiC were applied on various steel grades.

ARXPS-analysis and morphology of sputtered nanocrystalline TiC/SiC coatings

ARXPS (angle resolved X-ray photoelectron spectroscopy) measurements are used to obtain informations about surfaces and grain boundaries. Data acquired from nanocrystalline carbidic hard coatings have been employed to establish structural models. Magnetron-sputtered coatings of TiC, SiC and TiC/SiC were examined. In such coatings, partly defective TiC nanocrystallites are surrounded by interfacial carbide. This excess carbon shows a binding state similar to that of doped graphite or fullerenes. X-ray amorphous SiC is found in the residue. On top of sputtered SiC coatings, less oxide and graphite is found as compared to TiC/SiC or TiC coatings.

COMPARISON OF SLIDING WEAR RESISTANCE OF PLASMA ENHANCED CVD MULTILAYER COATED TiN AND TiC ON TOOL STEEL

The sliding wear resistance of single layer and multilayer TiN and TiC coatings produced by plasma enhanced CVD on tool steel has been evaluated using a washer on disc test method. The relative pelformances of the coatings were studied using X-ray diffractometric characterisation and observation byscanning electron microscopy. The wear behaviour of the coated specimens was such that: all the coated specimens showed better wear resistance than the blank material but with varying degrees of improvement, TiN coatings were superior to TiC, multilayer coatings were better than single layer coatings, and multilayer coatings having TiN as the outermost surface were better than those having TiC as the outermost surface. It was found that the fracture toughness of the coating and not its hardness determined wear resistance. This was confirmed by an indentation testing method.

Microstructural Development at Ti-Based Alloy/Coated SiC

ABSTRACTThe kinetics of formation of reaction layers at the interface between a Ti-based alloy (β-21s) and graphite blocks coated first, by CVD techniques, with a 100 μm layer of SiC and then either TiC or C were determined. The rate controlling step for reaction at 900°C and 10 MPa for up to 6 hours was found to be carbon diffusion through the reaction layer. The behaviour was found to be consistent with that of composite systems for prolonged heat treatment and the same growth behaviour was exhibited by both systems. Incubation times of 0.42 and 0.9 hours were determined for reaction layer growth in the TiC- and C-coated systems respectively. The reaction layer/Ti-alloy bond strength was good but all couples failed readily, especially if any C layers remained. The growth conditions of TiC coatings by reactive magnetron sputtering were determined for two different types of gas mixtures: CH4/Ar and C2H2/Ar. The composition and structure of the films were extensively studied.

Assessment of the reaction of SiC powders with iron-based alloys

The degree of reaction and dispersion achieved when SiC powders are brought into contact with liquid iron-based alloys has been assessed by a levitation dispersion test. SiC was found to react rapidly with molten iron matrices to form iron silicides and graphite. Attempts to generate protective TiC or Al2O3 coatings on SiC in situ in liquid iron proved unsuccessful; neither was precoating SiC and Ni and/or Cu successful in providing protection against molten iron alloys. Unprotected SiC also reacted readily with iron in the solid state (1000–1200 °C). Precoating with Ni, however, provides protection and prevents SiC dissolution and suicide formation during sintering at such temperatures.

Subject index of volumes 61 and 62

The purpose of this investigation is to determine the friction and wear behaviour of several PVD-coatings on steel against steel counterbodies under lubricated and unlubricated sliding conditions in dry and humid air and in vacuum. The aim is to minimise friction and wear by selecting suitable coatings and to optimise them in order to produce a self-lubricating system which needs no external source of lubricant.The experiments were performed by means of a model test system with a ball on disc tribometer with oscillating motion. Both friction and wear results are described as a function of coated sliding pair combination and test conditions. A wide variety of coating systems has been tested: TiN, TiC, TiCN, WN, WCN, TaN, TiAlN, CrN, soft metal and chalcogenide coatings and amorphous carbon (Me-C:H).The results showed that the friction and wear behaviour of PVD-coated steel sliding pairs is governed by the deposition variables, coating structure and the surrounding conditions (atmospheric humidity). The best results with respect to low friction coefficient and high wear resistance were achieved with carbon coatings.

Sliding wear resistance of TiCN coatings on tool steel made by plasma-enhanced chemical vapour deposition

In order to facilitate a proper choice of coating parameters for a wear-resistant TiCN coating on tool steel by plasma-enhanced chemical vapour deposition (PECVD), the sliding wear resistance of PECV deposited TiCN on tool steel was evaluated by the washer-on-disc method. A Taguchi array was employed to reveal the influence of coating parameters on wear resistance. The results showed that the deposition temperature and the flow rates of Ar and CH 4 were the dominant coating parameters for a TiCN coating for wear resistance. Optimizing the coating parameters of a TiCN coating for better load-carrying capacity and reducing the chance for deep galling resulted in the improvement of wear resistance beyond that of TiN and TiC coatings. Controlling the constituents of the TiCN coating proved to be easy, so that TiCN can be applied to meet the requirements if different wear conditions are needed.

Texture analyses of chemically vapor deposited coatings in the Ti-C-N system by wide film Debye-Scherrer X-ray diffraction technique

Texture analyses were performed on the chemically vapor deposited monolithic TiN, TiC, TiC x N y coatings and graded TiN/TiC coatings by wide film Debye-Scherrer X-ray diffraction technique. The preferred orientations of the coatings were investigated as a function of coating thickness and input gas composition. The growth of TiN and TiC coatings was initiated as randomly oriented crystallites which subsequently grew into large columnar grains with a preferred orientation. The textures of TiC coatings with the same thickness changed from the orientation to the orientation with decreasing hydrogen concentration in the gas phase. TiC x N y coatings exhibited a preferred orientation of up to the CH 4 /CH 4 +N 2 ratio of 0.14 above which a strong texture developed. The texture analyses on the graded TiN/TiC coatings showed that the TiC top layers were oriented in a direction perpendicular to the sample surface

Structure and morphology of laser assisted chemical vapour deposited TiC coatings

Titanium carbide has been deposited on silica substrates by pyrolytic laser chemical vapour deposition (LCVD) using a cw CO 2 laser and a reactive atmosphere consisting of TiC 4 , CH 4 and H 2 . The partial pressures of the gaseous components were kept constant in all the experiments at 7, 21 and 130 torr, respectively, while the laser power density and the interaction time were varied in the ranges 90-190 W.cm -2 and 15-40 s. The films were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and stylus profilometry. In the range of the deposition parameters investigated, it is shown that preferentially (200) oriented films have been produced. From the profilometric analyses, an apparent activation energy of about 86 kJ/ mole for the kinetics of film deposition has been deduced

Residual stresses in chemically vapor deposited coatings in the Ti-C-N system

Residual stresses in chemically vapor deposited monolithic and graded coatings in the Ti-C-N system were investigated as a function of substyate material and coating composition by X-ray diffraction Sin 2 ψ method. The thermal expansion coeffiicients (CTES) of the graphite substrates ranged from 2.5×10 -6 K -1 to 8.6×10 -6 K -1 . Titanium nitride (CTE 9.35×10 -6 K -1 ) and titanium carbide (CTE 7.5×10 -6 K -1 ) coatinqg deposited on the low-expansion substrates (CTEs 2.5-3.5×10 -6 K -1 ) exhibited crack networks which accounted for low stress levels measured in the coatings. A phenomenalogical explanation of the crack patterns was given. The coatings grown on the substrates with high coefficients of thermal expansion (CTEs 7.8-8.6×10 -6 K -1 ) had no cracks. Residual stresses in the TiN coatings on these substrates were measured to be tensile. Whereas TiC coatings always exhibited compressive stresses ranging from -54±10 MPa to -288±18 MPa. The TiC x N y coatings deposited on the substrate with a thermal expansion coefficient of 8.6×10 -6 K -1 also had compressive stresses increased with increasing TiC mole fraction in the TiC x N y up to about 0.9 above which stresses decreased. The residual stresses in the top TiC layers of the graded TiN/TiC coatings with linear, parabolic and exponentional composition profiles grown on the the same substrate (CTE 8.6×10 -6 K -1 ) were measured to be compressive and about 475 MPa. Stresses in the coatings were calculated and attributed to the thermal expansion mismatch between the coating and the substrate. It was shown that the measured stresses were, in general, found to be in good agreement with the calculated ones

Behavior of low- Z materials during plasma disruption simulated by laser beam

The behaviors of graphite, C/C composites and TiC coatings have been tested under near plasma disruption conditions simulated by intense laser beam. Low- Z materials used in the present experiments were G3 and ISO-880U graphite, three kinds of 3D carbon fiber reinforced carbon composites (3D-C/C) and CVD TiC coatings on Mo and G3 graphite. The plasma disruption simulation was carried out with a Nd:YAG laser. The duration of the laser pulse was 0.1 ms while the incident laser energy density on the specimens was up to 1.89 MJ/m 2 for a single laser pulse. So the incident laser power density was up to 1.89 MW/cm 2 during 0.1 ms and the corresponding value of t 1/2 was up to 18.91 kJ/(cm 2 s 1/2 ), whereis the power density of the incident laser (kW/cm 2 ) and t is the duration of the laser pulse (s). The weight loss and crater depth on the specimens and microstructure photographs of radiated specimen surfaces are given in the paper.

Acoustic emission study of failure mechanisms in TiC thermal barrier coatings

The failure mechanisms of thick plasma-sprayed TiC coatings subjected to severe thermal shocks were investigated using acoustic emission (AE), detected during and after the thermal shocks. The AE signal was triggered at the onset of the thermal shock and was completely captured for time durations up to 3 s. Signals were then studied and quantified directly by integrating the square of the waveform signals ( i.e. calculating the electrical energy). This method was compared with the more classical ringdown counting and with the maximum-amplitude method. The electrical energy demonstrated the best results that could be correlated to physical events. Besides the coating segmentation, two modes of delamination were observed: a sudden delamination during heating due to the bending of the coating under compressive stresses and a progressive delamination during cooling after plastic deformation had taken place at a high temperature during the thermal shocks.