TiCxNy and TiCx-TiN films obtained by CVD in an ultrasonic field

TiC _x N _y mono- and TiC_x-TiN double-layer films with a thickness of 30 to 100 m were prepared on a carbon steel (C: 0.6 to 0.7%) substrate by CVD in an ultrasonic field (ultrasound frequency: 19kHz; power: 10 to 20Wcm^–2). The moderate deposition conditions for obtaining an adherent and thick film of TiC _x N _y were: substrate temperature: 1050° C; H₂, N₂, TiCl₄ and CH₄ flow rates: 6.2, 4.0, 0.9 and 0.26 to 2.0 ml sec^–1, respectively. The growth rate, grain size and degree of 2 2 0 preferred orientation were found to decrease with increase in CH₄ concentration. TiC _x N _y film on carbon steel had a Vickers microhardness of 1800 to 2600 and an adhesion strength to the substrate of more than 120 kg cm^–2. A TiC _x -TiN (x0.5) double-layer film was obtained at 1050° C by a controlled alternative deposition of TiC _x or TiN. Quasiepitaxial growth of crystallites in the double layers was found to prevail in both coatings of TiC _x (220)/TiN (220)/steel and TiN (200)/TiC_x (200)/steel.     

High-pressure sintering of cubic boron nitride

Cubic boron nitride (cBN) powder was compacted at high pressure and high temperature using a solid solution of titanium carbide and titanium nitride (TiC _x N_1–x ) as binding material in the presence of a small amount of aluminium. Different compositions of (TiC _x N_1–x ), 0<x<1 were used as binders. The weight percentage of cBN, TiC _x N_1–x and aluminium were optimized and found to be critical; any marked deviation from these optimized values deteriorated the quality of compacts. Various high-pressure sintering parameters such as pressure, temperature and sintering time, etc, were optimized for this binder. The compacts were also characterized using X-ray diffraction, scanning electron microscopy and microhardness measurements. The microstructural and X-ray diffraction observations indicated no marked changes in the compacts as the value ofx in TiC _x N_1–x was varied, but the microhardness was found to depend on the value ofx.     

Effect of nano-CeO2 on microstructure properties of TiC/TiN+TiCN-reinforced composite coating

TiC/TiN+TiCN-reinforced composite coatings were fabricated on Ti–6Al–4V alloy by laser cladding, which improved surface performance of the substrate. Nano-CeO₂ was able to suppress crystallization and growth of crystals in the laser-cladded coating to a certain extent. With the addition of proper content of nano-CeO₂, this coating exhibited fine microstructure. In this study, Al₃Ti+TiC/TiN+nano-CeO₂ laser-cladded coatings have been studied by means of X-ray diffraction and scanning electron microscope. X-ray diffraction results indicated that Al₃Ti+TiC/TiN+nano-CeO₂ laser-cladded coating consisted of Ti₃Al, TiC, TiN, Ti₂Al₂₀Ce, TiC_0·3N_0·7, Ce(CN)₃ and CeO₂, this phase constituent was beneficial in increasing microhardness and wear resistance of Ti–6Al–6V alloy.     

Interfacial study of magnesium-containing fluoridated hydroxyapatite coatings

Magnesium-containing fluoridated hydroxyapatite (Mg_xFHA) coatings have been developed to improve the biological performances of fluoridated hydroxyapatite (FHA) coatings. The coatings are deposited on Ti6Al4V substrates via a sol-gel process. The interface between the coating and substrate is characterized by scanning electron microscopy, glow discharge optical emission spectroscopy and X-ray photoelectron spectroscopy for coating thickness, elemental distribution and chemical states. Pull-off test is used to evaluate the adhesion strength. The results show that the interdiffusion of elements happens at the coating/substrate interface. The incorporation of Mg ions into FHA coatings enhances the pull-off adhesion strength between the coating and the substrate, but no significant difference is observed with different Mg concentrations.     

Effect of nano-CeO2 on microstructure properties of TiC/TiN+nTi(CN) reinforced composite coating

TiC/TiN+TiCN reinforced composite coatings were fabricated on Ti?C6Al?C4V alloy by laser cladding, which improved surface performance of the substrate. Nano-CeO₂ was able to suppress crystallization and growth of the crystals in the laser-cladded coating to a certain extent. With the addition of proper content of nano-CeO₂, this coating exhibited fine microstructure. In this study, the Al₃Ti+TiC/TiN+nano-CeO₂ laser-cladded coatings were studied by means of X-ray diffraction and scanning electron microscope. The X-ray diffraction results indicated that the Al₃Ti+TiC/TiN+nano-CeO₂ laser-cladded coating consisted of Ti₃Al, TiC, TiN, Ti₂Al₂₀Ce, TiC_0·3N_0·7, Ce(CN)₃ and CeO₂, this phase constituent was beneficial to increase the microhardness and wear resistance of Ti?C6Al?C6V alloy.     

Thermal stability of interfaces in Ti-6Al-4V reinforced by SiC Sigma fibres

Interfacial reactions in Ti-6Al-4V/SiC Sigma fibres (coated with carbon and TiB₂) were studied at different temperatures (600, 700 and 1000 °C). Interface microstructure was investigated by scanning electron microscopy and Auger electron spectroscopy. A simulation of the chemical phenomena occurring at the interfaces was carried out using powders of pure titanium, carbon and TiB₂; the reaction products were identified by X-ray diffraction. The double coating of Sigma fibres is effective in delaying detrimental reactions with the matrix. At the interfaces matrix/TiB₂ and TiB₂/C, the TiB and TiC_x phases form, respectively. The protective coating of fibres shows a lifetime greater than 1000 and 750 h at 600 and 700 °C, respectively.     

Microstructure of high velocity oxy-fuel sprayed Ti2AlC coatings

The microstructure formation and phase transformations in Ti₂AlC-rich coatings deposited by High Velocity Oxy-fuel spraying of Maxthal 211^? powders is presented. High resolution electron microscopy analysis, using both scanning and transmission electron microscopy with energy dispersive spectrometry and energy filtering, combined with X-ray diffraction reveals that the coatings consist of Ti₂AlC grains surrounded by regions of very small TiC grains embedded in Ti _x Al _y . The composition of the Ti _x Al _y depends on its surrounding and varies with size and distribution of the adjacent TiC grains. Impact of spray parameters on coating microstructure is also discussed. Two spray parameters were varied; powder size distribution and flame power. They were found to greatly affect the coating microstructure. Increasing powder size and decreasing flame power increase the amount of Ti₂AlC, but produces thinner coatings with lower cohesion. Larger powder size will also decrease oxygen incorporation.     

Effect of substrate bias voltage on structural and mechanical properties of pulsed DC magnetron sputtered TiN-MoSx composite coatings

TiN-MoS_x composite coatings were deposited by pulsed DC closed-field unbalanced magnetron sputtering (CFUBMS) using separate Ti and MoS₂ targets in an Ar and N₂ gas environment. The effect of substrate bias voltage on the structure and mechanical properties of TiN-MoS_x composite coating has been studied. The structure and composition of the coating were evaluated using field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS) by X-ray and grazing incidence X-ray diffraction (GIXRD). Scratch adhesion tests, Vickers microhardness tests and ball-on-disc tests with a cemented carbide (WC-6%Co) ball were carried out to investigate mechanical properties of the coating. Application of substrate bias was found to transform the structure of TiN-MoS_x composite coating from open columnar to a dense columnar structure. The changes in grain size and texture coefficient appear to be associated with variation in substrate bias voltage. The mechanical properties of the coating such as adhesion and composite microhardness were also observed to be related to the change in bias voltage. A maximum hardness of 22 GPa was obtained for a coating deposited at substrate bias voltage of −40 V. The improved structural and mechanical properties of the coating deposited at −40 V were also reflected in its excellent wear resistance property.     

Thermal stability of CrN<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> nanometric coatings deposited on stainless steel

Thin CrN _x coatings are often used as protective coatings for steel. In these applications, coated parts might be subjected to high temperatures that can alter the coatings structural and mechanical properties. In this work, the properties of nanometric CrN _x coatings deposited by reactive magnetron sputtering on AISI 304L stainless steel were studied by transmission electron microscopy, glazing incident X-ray diffraction, Atomic Force Microscopy, and nanoindentation. The effect of annealing, both in air and vacuum, on the coating crystal structure, surface morphology and hardness were also investigated. It was found that annealing in vacuum-induced phase transformation from CrN to Cr₂N, while after annealing in air only Cr₂O₃ phase was present. Surface roughness did not increase for annealing in vacuum. CrN _x coatings with higher Cr₂N phase content showed lower roughness increase for annealing in air. Measured hardness was >10 GPa for as-deposited CrN _x samples. An increase in hardness up to >20 GPa was found for vacuum-annealed samples.     

Microstructural study of oxidation of carbon-rich amorphous boron carbide coating

Carbon-rich amorphous boron carbide (B _x C) coatings were annealed at 400°C, 700°C, 1000°C and 1200°C for 2 h in air atmosphere. The microstructure and composition of the as-deposited and annealed coatings were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), micro-Raman spectroscopy and energy dispersive X-ray spectroscopy (EDS). All of the post-anneal characterizations demonstrated the ability of carbon-rich B _x C coatings to protect the graphite substrate against oxidation. Different oxidation modes of the coatings were found at low temperature (400°C), moderate temperature (700°C) and high temperature (1000°C and 1200°C). Finally, the feasibility of the application of carbon-rich BxC instead of pyrolytic carbon (PyC) as a fiber/matrix interlayer in ceramics-matrix composites (CMCs) is discussed here.     

Corrosion behaviour of steel with PVD CrxN coatings

The application of PVD coatings for wear protection of tools is well known. Since many years, TiN coated cutting and forming tools are state of the art. In contrast, the application of PVD coatings on machine parts is not standard today. This is caused by the problems of coating deposition on components as well as the fact that wear protection and corrosion protection is demanded for many parts with longer lifetime. TiN produced by means of PVD technique is good for wear protection, but with respect to corrosion there are problems. On the other hand electropolated chromium is a reliable coating to resist corrosion, but wear resistance is limited. PVD Cr_xN coatings promise to combine the advantages of hard coatings and electropolated chromium. The present study focuses on the corrosion properties of magnetron sputtered Cr_xN coatings. Different types of coatings on steel substrates with various amounts of nitrogen were investigated in order to take into account aspects of coating deposition resp. coating material, coating structure and coating morphology. Additionally several graded and multilayer coatings were studied to show influences of coating system design. Electroplated hard chromium was used as reference material for corrosion resistance. To explain the corrosion behaviour, crystallographic phases and structure of coatings were analysed by X‐ray diffraction and morphology by SEM. It could be shown that the corrosion behaviour depends on all these parameters and that 8 μm chromium nitride provides the same corrosion protection as 48 μm electroplated chromium.     

Study of growth rate and failure mode of chemically vapour deposited TiN,TiCxNy and TiC on cemented tungsten carbide

The effects of deposition temperature and mole ratio of CH₄ to TiCl₄ on the growth rate of titanium compound coatings were investigated. Activation energies of TiN, TiC _x N _y and TiC deposition reactions of 4.8×10⁴, 1.9×10⁵ and 2.8×10⁵ J mol^–1, respectively, were obtained experimentally. The carbon content of TiC _x N _y deposit was increased as the CH₄ flow rate and deposition temperature increased. It was found that TiC _x N _y grain size was finer than TiC and TiN.The cutting temperatures of TiN-coated and TiC-coated tools were 10% (TiN) and 20% (TiC) lower than that of uncoated tools. Feed force and reaction force of coated tools were 30% and 18% less than those of uncoated tools, respectively. The dominant failure mode of coated tools was due to the microchipping of the cutting edge.     

The influences of B dopant on the crystal structure and nucleation ability of TiCx in the Al melt

The influences of B dopant on the crystal structure of TiC_x and nucleation efficiency on α-Al are investigated in this paper. It was found that B solute atoms in the melt easily diffused into the crystal lattice of TiC_x, meanwhile the f.c.c. crystal structure was preserved according to the EDS and TEM analysis. The doping effect of B in TiC_x was reflected on the X-ray diffraction (XRD) patterns, in which the diffraction peak of (2 0 0) plane rose correspondingly. TiC_x showed strong (1 1 1) orientation, but shifted to strong (2 0 0) after trace B doped. Furthermore, the grain refining ability of TiC_x with strong (2 0 0) orientation induced by B dopant on commercial pure Al was improved obviously and the excellent refining performance was kept in a long holding time, which indicated that the structural stability of TiC_x was enhanced after B doped.     

Interaction between the TiC(TiCN)-Ni-Mo hardmetals and chromium vapours

The interaction between TiC or TiCN-based hardmetals with a Ni-Mo binder, or cermets, and chromium vapour in a vacuum was investigated over a wide temperature range acceptable for depositing wear-resistant coatings without the formation of a liquid phase in the cermets. Computer modelling in the Ti-C-Cr system showed that a direct interaction of TiC with chromium, leading to the formation of chromium carbides, is not possible because of the high thermodynamic stability of titanium carbide. It was established experimentally that as a result of the interaction between the cermets and chromium vapours, a coating characterized by a two-layer structure was deposited on the cermet surface. The coating consists of an inner layer adjacent to the substrate, which is composed of the chromium and carbon solid solution in nickel, and an outer layer composed of a mixture of (Cr, Ni)₇C₃ and (Cr, Ni)₂₃C₆. The activation energy of the deposition process is 387 kJ mol^–1 which is close to the value of the chromium heat of evaporation. The coating deposition process is supposed to be limited by the rate of the external supply of chromium from the vapour phase. The results of the investigation of the structure, composition and morphology of the coating are presented. A mechanism responsible for the interaction of the cermets with chromium vapour leading to the formation of the two-layer coating, is proposed.     

Effects of substrate bias voltage and target sputtering power on the structural and tribological properties of carbon nitride coatings

Effects of substrate bias voltage and target sputtering power on the structural and tribological properties of carbon nitride (CN_x) coatings are investigated. CN_x coatings are fabricated by a hybrid coating process with the combination of radio frequency plasma enhanced chemical vapor deposition (RF PECVD) and DC magnetron sputtering at various substrate bias voltage and target sputtering power in the order of −400 V 200 W, −400 V 100 W, −800 V 200 W, and −800 V 100 W. The deposition rate, N/C atomic ratio, and hardness of CN_x coatings as well as friction coefficient of CN_x coating sliding against AISI 52100 pin in N₂ gas stream decrease, while the residual stress of CN_x coatings increases with the increase of substrate bias voltage and the decrease of target sputtering power. The highest hardness measured under single stiffness mode of 15.0 GPa and lowest residual stress of 3.7 GPa of CN_x coatings are obtained at −400 V 200 W, whereas the lowest friction coefficient of 0.12 of CN_x coatings is achieved at −800 V 100 W. Raman and XPS analysis suggest that sp³ carbon bonding decreases and sp² carbon bonding increases with the variations in substrate bias voltage and target sputtering power. Optical images and Raman characterization of worn surfaces confirm that the friction behavior of CN_x coatings is controlled by the directly sliding between CN_x coating and steel pin. Therefore, the reduction of friction coefficient is attributed to the decrease of sp³ carbon bonding in the CN_x coating. It is concluded that substrate bias voltage and target sputtering power are effective parameters for tailoring the structural and tribological properties of CN_x coatings.     

Electrical resistivities in single crystals of TiC x and VC x

TiC _x and VC _x have wide non-stoichiometric composition ranges which come only from the carbon vacancies. High purity single crystals with controlled compositions were prepared, and their electrical resistivities at 4.2 and 298 K were measured as a function of composition. In the case of TiC _x whose carbon vacancies are disordered in the lattice, the dependence of the residual resistivity on the composition was interpreted' by applying Nordheim's rule to the vacancy scattering and by considering the change in carrier density due to the introduction of vacancies. In addition, the difference in the resistivity between 4.2 and 298 K was discussed. In the case of VC _x whose carbon vacancies are ordered, the dependence of the resistivity on the composition ranges of the ordered phases was examined in detail.     

On the crystal structures of the intermetallic system Cr1+δSb|Fe1+δSb: A combined single crystal X-ray and neutron diffraction study

As an extension of X-ray powder-diffraction and magnetic susceptibility measurements we present a single crystal study of the NiAs-type intermetallic compounds, (Cr_1?xFe_x)_1+δSb (0 ? x ? 1), with the view of obtaining a better understanding of the magnetic behaviour. In this paper the initial work concerning X-ray and neutron diffraction investigations to determine δ-values and chromium to iron ratios is reported.     

Nitridation of the sol-gel derived TiO2 coating films and the infrared ray reflection

The titanium nitride coating film was prepared on the SiO₂ glass substrate by ammonolysis of titanium dioxide coating film formed by sol-gel method. The X-ray diffraction (XRD) pattern indicated that it is cubic titanium nitride with a lattice parameter,a _o, of 0.4231 nm. The obtained titanium nitride is non-stoichiometric (TiN _x x≤ 1) because the value, 0.4231 nm, is smaller than the stoichiometric one (0.4240 nm). The coating film show very high infrared (i.r.) reflectance in the wavelength region of 2–8 μm.     

Interfacial structure, residual stress and adhesion of diamond coatings deposited on titanium

The interfacial structures of diamond coatings deposited on pure titanium substrate were analyzed using scanning electron microscopy and grazing incidence X-ray diffraction. Results showed that beneath the diamond coating, there was one titanium carbide and hydride interlayer, followed by a heat-affected and carbon/hydrogen diffused Ti layer. Residual stress in the diamond coating and TiC interlayer under different process parameters were measured using Raman and X-ray diffraction (XRD) methods. Diamond coatings showed large compressive stress on the order of a few giga Pascal. XRD analysis also showed the presence of compressive stress in the TiC interlayer and tensile stress in the Ti substrate. With increasing deposition duration, or decreasing plasma power and concentration of CH₄ in gas mixture, the compressive residual stress in the diamond coating decreased. The large residual stress in the diamond coating resulted in poor adhesion of the coatings to substrate, but adhesion was also related to other factors, such as the thickness and nature of the TiC interlayer, etc. A graded interlayer design was proposed to lower the thermal stress, modify the interfacial structure and improve the adhesion strength.     

High‐Performance Microwave‐Derived Multi‐Principal Element Alloy Coatings for Tribological Application

The authors report the development of Al_xCoCrFeNi (x = 0.1 to 3) high entropy alloy (HEA) coatings using a simple and straightforward microwave technique. The microstructure of the developed coatings is composed of a cellular structure and diffused interface with the substrate. The microstructure of the HEA coatings varies as a direct function of Al content. An increase in Al fraction shows structural transformation from FCC to BCC along with the evolution of σ and B₂ as the major secondary phases. The diffusion of Mo from the substrate enhances the mixing entropy and promotes σ‐phase formation. The HEA coatings show significantly high hardness compared to SS316L substrate steel (227 HV) with a maximum value of 726 HV observed for three‐molar composition. The fracture toughness exhibits an inverse correlation with the Al fraction with the highest value of around 49 MPa m^1/2 observed for Al_0.1CoCrFeNi coating. The equimolar coating composition shows lowest erosion rates among all the tested samples due to optimum combination of the mechanical properties. The erosion resistance of the equimolar coating is 2 to 5 times higher than steel substrate and around 1.5 times higher than the non‐equimolar counterparts depending upon the impingement angles.