Residual stress control in CrAlN coatings deposited on Ti alloys

In order to control residual stress of CrAlN coatings on Ti substrates, ~70 nm CrAl interlayer was deposited at different temperatures. Residual stress and coatings’ structure were characterized by X-ray diffraction. Residual stress in the coatings was compressive and increased with CrAl interlayer deposition temperature. Residual stress in 1.5 µm, 2 µm and 2.6 µm thick CrAlN films on TC21 with the interlayer deposited at 100 °C (?47.43 MPa, ?25.57 MPa and ?855.77 MPa, respectively) was smaller than with the interlayer deposited at 300 °C (?1.39 GPa, ?1.95 GPa and ?1.62 GPa, respectively). The coatings on the TC4 substrate showed the same trend (?1.02 GPa, ?389.91 MPa and ?1.03 GPa for the interlayer deposited at 100 °C, respectively, and ?921.42 MPa, ?2.31 GPa and ?1.80 GPa for the interlayer deposited at 100 °C, respectively). Changing the interlayer deposition temperature can influence the coatings’ residual stress and crystal structure, and improve mechanical properties of the coatings. CrAlN deposition is a convenient and efficient way to improve mechanical properties of Ti alloys.     

Substrate effect on wear resistant transition metal nitride hard coatings: Microstructure and tribo-mechanical properties

Four types of different hard transition metal nitrides (TMN:ZrN, CrN, WN and TiN) coatings were deposited on Si (100) and 316LN stainless steel substrates using DC magnetron sputtering. A comprehensive study of microstructure and substrate dependent tribo-mechanical properties of TMN coatings was carried out. Higher hardness (H) and elastic modulus (E) were obtained for WN (H=40 GPa and E=440 GPa) and TiN (H=30 GPa and E=399 GPa) coatings. This is related to the formation of (100) and (111) preferred orientations in WN and TiN coatings, respectively. However, the less hardness and elastic modulus were obtained for ZrN and CrN coatings where (200) orientation is preferred. Remarkably, low friction coefficient (0.06–0.57) and higher wear resistance in the coatings deposited on steel substrates are directly associated with the higher resistance to plastic deformation (H³/E²) and the presence of intrinsic compressive stress. Three body wear modes enhanced the friction coefficient (0.15–0.62) and the wear rate in the coatings deposited on Si substrates. This is primarily associated with low fracture toughness of brittle single crystalline Si (100) substrates. Steel-on-steel contact was dominated in ZrN/steel sliding system. This occurs due to the severe adhesive wear mode of steel ball, whereas, the abrasive wear modes were attained for the CrN, WN and TiN coatings sliding against steel balls.     

Tribological study of amorphous BC4N coatings

Amorphous BC₄N thin films with a thickness of ∼ 2 μm have been deposited by Ion Beam Assisted Deposition (IBAD) on hard steels substrates, in order to study the wear behavior under high loads and the applicability as protective coatings. The bonding structure of the a-BC₄N film was assessed by X-ray Absorption Near Edge Spectroscopy (XANES) and Infrared Spectroscopy, indicating atomic mixing of B–C–N atoms, with a proportion of ∼ 70% sp² hybrids and ∼ 30% sp³ hybrids. Nanoindentation shows a hardness of ∼ 18 GPa and an elastic modulus of ∼ 170 GPa. A detailed tribological study is performed by pin-on-disk tests, combined with spectromicroscopy of the wear track at the coating and wear scar at pin. The tests were performed at ambient conditions, against WC/Co counterface balls under loads up to 30 N, with the sample rotating at 375 rpm. The coatings suffer a continuous wear, at a constant rate of 2 × 10^− 7 mm³/Nm, without catastrophic failure due to film spallation, and show a coefficient of friction of ∼ 0.2.     

Diamond-like carbon overcoat for TFMH using filtered cathodic arc system with Ar-assisted arc discharge

The deposition system described for sub-30 Å and thicker carbon (ta-C) overcoat that includes two RF ion beam guns and Filtered Cathodic Arc (FCA) module mounted on a single vacuum chamber. The system is capable of flattening the Thin Film Magnetic Heads (TFMH) surface by ion beam etching; smoothing scratches, trenches, steps on boundaries of different materials, and enhancing the adhesion by ion assisted ion beam sputtering. It provides the highly controllable deposition of carbon using an FCA module with Ar-assisted arc discharge. Low-level particulates are achieved on the deposited film surface (< 5/cm² ). It was shown that crucial impact on filtering the particles with size < 1 μm has the electrostatic field distribution across the plasma guide that can be controlled by duct bias. Mechanical and electrical properties, optical and Raman spectra of ta-C films were investigated as a function of Ar flow in the arc discharge area. At Ar flow rates 0–12 sccm, stress of the films was varied in a range 2.9–7.5 GPa while hardness and Young's Modulus stayed in ranges of 45–60 GPa, and 230–300 GPa, respectively. Density of the obtained films was greater than 2.8 g/cm³. Optical absorption and electrical conductivity of ta-C films showed a significant rise while stress came down with Ar flow. Raman G-peak was higher for ta-C films with lower stress and shifted to lower energy. The low stress films versus high stress films showed a few orders reduced electrical resistance and anisotropy of specific resistance with respect to substrate plane: ρ_⊥ ≫ ρ_∥. In situ ellipsometric control of growing film thickness was implemented on the system. Run-to-run standard deviation was less than 1 Å for 20–25 Å thick films. High corrosion resistance of FCA coatings was exhibited. The impact of Ar gas–carbon plasma interaction on the deposition conditions and microstructure of ta-C films was discussed.     

Electrical properties and energy-storage performance of (Pb0.92Ba0.05La0.02)(Zr0.68Sn0.27Ti0.05)O3 antiferroelectric thick films prepared by tape-casing method

The energy-storage performance and dielectric properties of tape-cast (Pb_0.92Ba_0.05La_0.02)(Zr_0.68Sn_0.27Ti_0.05)O₃ (PBLZST) antiferroelectric (AFE) thick films with different thicknesses were systematically studied. As the thickness of the thick films increased from 40 to 80 µm, the dielectric constant and saturation polarization (P_s) of the thick films were gradually increased, while their corresponding breakdown strength (BDS) was decreased. A maximum recoverable energy-storage density of 6.8 J/cm³, companied by an efficiency of 61.2%, was achieved in the PBLZST AFE thick film with a thickness of 40 µm at room temperature. Moreover, the energy density of the PBLZST AFE thick films also displayed good thermal stability over 25–200 °C. In addition, all the samples had a low leakage current density of ~10⁻⁶ A/cm² at room temperature. These findings demonstrated that the PBLZST thick films should be a promising candidate for applications in high energy-storage capacitors.     

Electrohydrodynamic atomization deposition and mechanical polishing of PZT thick films

In this work, electrohydrodynamic atomization deposition, combined with mechanical polishing, was used for the fabrication of dense and even PZT thick films. The PZT slurry was ball-milled and the effect of milling time on the characteristics of the deposited films was examined. A time of 50 h was found to be the optimum milling time to produce dense films. It was found that the PZT thick films presented rough surface after deposition. In order to overcome this drawback the mechanical polishing process was employed on the deposited films. After the mechanical polishing the roughness (Ra) and peak-to-peak height (Rz) of the film surface were decreased from 422 nm to 23 nm and from 5 µm to 150 nm, respectively. Subsequently, an increase of ~10 pC N⁻¹ on piezoelectric constant (d_{33, f}) was obtained. In addition, it was observed that the d₃₃ was increased from 57 pC N⁻¹ to 89 pC N⁻¹ when the thickness was increased from 10 µm to 80 µm.     

Mechanical and electrical properties of micron-thick nitrogen-doped tetrahedral amorphous carbon coatings

The effect of nitrogen doping on the mechanical and electrical performance of single-layer tetrahedral amorphous carbon (ta-C:N) coatings of up to 1 μm in thickness was investigated using a custom-made filtered cathode vacuum arc (FCVA). The results obtained revealed that the hardness and electrical resistance of the coatings decreased from 65 ± 4.8 GPa (3 kΩ/square) to 25 ± 2.4 GPa (10 Ω/square) with increasing nitrogen gas ratio, which indicates that nitrogen doping occurs through substitution in the sp² phase. Subsequent AES analysis showed that the N/C ratio in the ta-C:N thick-film coatings ranged from 0.03 to 0.29 and increased with the nitrogen flow rate. Variation in the G-peak positions and I(D)/I(G) ratio exhibit a similar trend. It is concluded from these results that micron-thick ta-C:N films have the potential to be used in a wide range of functional coating applications in electronics.     

Comparison of the anti-coking performance of CVD TiN,TiO2 and TiC coatings for hydrocarbon fuel pyrolysis

Previous work has shown that both TiN and TiO₂ coatings can inhibit the metallic catalytic coking effectively, but both of them have their own shortage. In this work, TiC coating was prepared on the surface of SS304 tube using TiCl₄-CH₄-H₂ by CVD method. Its morphology, elemental composition, thickness and oxidation resistance were characterized by SEM, EDX, metalloscopy and TPO tests, respectively. The results show that CVD TiC coating is gray, homogeneous, and dense without cracks or holes. The TiC coating presents a cuboid particle structure with the sizes of about 1.0 µm for the cuboid crystals, and the Ti/C ratio close to 1:1, while the average thickness is about 11.62 µm. TPO results show that the TiC coating begins to react with O₂ and release CO₂ at about 810 °C. Compared with the TiN coating (The initial oxidation temperature of TiN is about 350 °C), the oxidation resistance of TiC coating is improved substantially. As a conclusion, the high oxidation resistance order is TiO₂ coating>TiC coating>TiN coating. Furthermore, the temperature programmed cracking of RP-3 Chinese jet fuel was employed to compare the anti-coking performance of TiN, TiO₂ and TiC coatings. The results show that each of TiN, TiO₂ and TiC coating has obvious anti-coking effect, and the anti-coking performance order is TiN coating=TiC coating>TiO₂ coating.     

Tribological behaviour of RF-magnetron sputter deposited hydroxyapatite coatings in physiological solution

The aim of the paper is to explore the tribological performance of hydroxyapatite (HA) coatings deposited by radio frequency (RF) magnetron sputtering on AZ31 magnesium alloy (96% Mg, 3% Al, 0.7% Zn, 0.3% Mn) for biomedical applications. In this study, the position of the samples on a substrate holder, relative to a target erosion zone was taken into consideration in order to elucidate its impact on the coating characteristics, such as composition, morphology, surface topography and tribology. Substrate rotation and arc-movement were foreseen in the experimental set-up to increase the uniformity of thin film properties. The deposited HA thin films were revealed to exhibit an increase of the Ca/P ratio from 1.83 to 1.97, a decrease of (002) texture and thickness, as the samples were shifted towards the target erosion zone. By coatings, the roughness of Mg alloy was decreased (R_{a Mg alloy}=31.3 nm; R_{a coating}=29 nm and 21 nm). The coating placed in the centre of the substrate holder showed high hardness and Young's modulus (H =8.3±0.9 GPa; E=89±10 GPa) than the coating prepared under the target erosion zone (H =6.9±1.1 GPa; E=75±6 GPa). The coating deposited under target erosion zone exhibits superior friction behaviour in simulated body fluid environment, with the friction coefficient (μ) of 0.184, while the sample located in the centre of the substrate holder possesses the friction coefficient (0.306) comparable to the AZ31 substrate (0.307). The low wear rate was determined in the case of coating deposited under target erosion zone (4.83×10⁻⁵ mm³ N⁻¹ m⁻¹) than uncoated AZ31 substrate (0.00518 mm³ N⁻¹ m⁻¹) or than coating placed in the centre of the substrate holder (0.00294 mm³ N⁻¹ m⁻¹).     

Nitrogenated carbon films deposited using filtered cathodic arc

Nitrogenated carbon films were deposited on various substrates using filtered cathodic arc. Non-uniformity of the film thickness was less than 5% over a 15 cm diameter area. Mechanical, optical (refraction index, extinction coefficient versus wavelength) and electrical properties were investigated as a function of nitrogen flow rate. Deposited coatings demonstrated high hardness of 40–65 GPa, Young's modulus 200–285 GPa, excellent elastic recovery, high critical pressure for scratch formation, and surface smoothness. While the hardness showed a relatively small decrease with nitrogen flow increase, the stress decrease was more significant (8–3.8 GPa). Extremely low wear rates were observed, even at high contact pressures, and no substantial debris was detected indicating that carbon is oxidized during wear. Clear correlation was found between transparency, electrical resistivity and stress of the films. Transparency and resistivity showed a significant rise with an increase of stress. An explanation of the film properties is based on the assumption that the basic characteristics of the deposited films were determined by the relative proportion of two three dimensional complementary type of bonds; the tetrahedral sp³ bonds leading to stiff networks, and the trigonal sp² arrangments close to fullerene-like, or nanotube-like, structures.     

785 nm Raman spectroscopy of CVD diamond films

Raman spectroscopy is a powerful technique often used to study CVD diamond films, however, very little work has been reported for the Raman study of CVD diamond films using near-infrared (785 nm) excitation. Here, we report that when using 785 nm excitation with 1 µm spot size, the Raman spectra from thin polycrystalline diamond films exhibit a multitude of peaks (over 30) ranging from 400–3000 cm^− 1. These features are too sharp to be photoluminescence, and are a function of film thickness. For films > 30 µm thick, freestanding films, and for films grown in diamond substrates the Raman peaks disappear. This suggests that the laser is probing the vibrations of molecular units at the grain boundaries of the disordered crystallites present at the interface between the diamond and substrate.     

Thermal-induced blister cracking behavior of annealed sandwich-structured TiN/CrAlN films

Sandwich-structured TiN/CrAlN films were rationally designed using metallic Ti and Al-Cr alloy targets by RF-pulsed magnetron sputtering. After obtained films were annealed at diverse temperatures at atmospheric pressure for 1 h, the hardness reveals an apparent decrease evolution from 29.2 to 15.7 GPa and H/E* ratio declines below 0.1 with increasing annealing temperature. Meanwhile, the grain size gradually becomes larger from 16.3 to 130.0 nm with increasing annealing temperature. Interestingly, it is observed that cracking behavior of sandwich-structured composite TiN/CrAlN films at elevated temperature is originated from the top of the blisters where main component is alumina on the surface, in virtue of intrinsically induced stress during oxidation, thermal expansion mismatch and phase transformation of the oxide layer. No cracks, nevertheless, are yielded in the film between any two blisters. Herein, these findings provide some beneficial references for preparing high quality films and coatings in high temperature service.     

Influence of substrate bias voltage on structure and properties of hard Si–B–C–N films prepared by reactive magnetron sputtering

We systematically investigated the effect of the rf induced negative substrate bias voltage, U_b, on characteristics of novel quaternary Si–B–C–N films. The films were deposited on Si(100) or glass substrates by reactive dc magnetron co-sputtering of silicon, boron and carbon from a single C–Si–B or B₄C–Si target in nitrogen–argon gas mixtures at substrate temperatures of 180–350 °C. Elemental compositions of the films, their surface bonding structure, and mechanical and electrical properties were primarily controlled by the U_b values, varied from a floating potential (being between − 30 and − 40 V) to U_b = − 700 V. The energy and flux of ions bombarding the target and the growing films were evaluated on the basis of the measured discharge characteristics. The films were found to be amorphous with thickness up to 5 μm and density around 2.4 g/cm³. They exhibited hardness up to 44 GPa, modified Young's modulus between 170 and 280 GPa, elastic recovery up to 82% and good adhesion to substrates at a low compressive stress (0.6–1.8 GPa). The results of stress measurements were compared with predictions of the model developed by Davis and a beneficial role of silicon in reducing the compressive stress in the films was proved. Electrical conductivity of the semiconductive Si–B–C–N films with a high (approximately 40 at.%) carbon content was controlled by the nitrogen–argon gas mixture composition and the U_b values.     

Very hard ZrC thin films grown by pulsed laser deposition

Thin ZrC films were grown on (1 0 0) Si substrates at temperatures from 30 to 500 °C by the pulsed laser deposition technique. Auger electron spectroscopy investigations found that films contained oxygen concentration below 2.0 at%, while X-ray photoelectron spectroscopy investigations showed that oxygen is bonded in an oxy-carbide type of compound. The films’ mass densities, estimated from X-ray reflectivity curve simulations, and crystallinity improved with the increase of the substrate temperature. Williamson–Hall plots and residual-stress measurements using the modified sin² ψ method for grazing incidence X-ray diffraction showed that the deposited films are nanostructured, with crystallite sizes from 6 to 20 nm, under high micro-stress and compressive residual stress. Nanoindentation investigations found hardness values above 40 GPa for the ZrC films deposited at substrate temperatures higher than 300 °C. The high density of the deposited films and the nm-size crystallites are the key factors for achieving such high hardness values.     

Effect of Ti particle size on mechanical and tribological properties of TiCN coatings prepared by reactive plasma spraying

Titanium carbonitride (TiCN) coatings were successfully fabricated by reactive plasma spraying (RPS) from agglomerated Ti-graphite feedstock. The effect of Ti particle size on the microstructure and phase composition of plasma sprayed TiCN coatings was investigated. The Vickers microhardness of coatings was measured by a Microhardness Test and the corresponding Weibull distribution were also analyzed. In addition, a pin-on-disk tribometer was employed to determine the trobological properties of coatings. Results show that all the coatings consist of TiC_xN_1−x (0 ≤ x ≤1) and minor Ti₂O phases, and the amount of Ti₂O increases with the increase of Ti particle size. The Weibull distribution of Vickers microhardness of all the coatings shows apparent scattering, while the coating sprayed with Ti particle size of 28 µm exhibits a relatively even distribution. Compared with the coating sprayed with Ti particle size of 14 µm or 48 µm, the coating sprayed with Ti particle size of 28 µm exhibits improved mechanical and tribological properties, which are attributed to the high microhardness and strong bonding strength.     

Deposition and characterization of diamond-like carbon films by microwave resonator microplasma at one atmosphere

Diamond-like carbon (DLC) films have been deposited at atmospheric pressure by microwave-induced microplasma for the first time. Typical precursor gas mixtures are 250 ppm of C₂H₂ in atmospheric pressure He. Chemically resistant DLC films result if the Si (100) or glass substrate is in close contact with the microplasma, typically at a standoff distance of 0.26 mm. The films deposited under this condition have been characterized by various spectroscopic techniques. The presence of sp³ CH bonds and ‘D’ and ‘G’ bands were observed from FTIR and Raman spectroscopy, respectively. The surface morphology has been derived from SEM and AFM and shows columnar growth with column diameters of approximately 100 nm. Likely due to the low energy of ions striking the surface, the hardness and Young's modulus for the films were found to be 1.5 ± 0.3 GPa and 60 ± 15 GPa respectively with a film thickness of 2 μm. The hypothesis that a high flux of low energy ions can replace energetic ion bombardment is examined by probing the plasma. Rapid deposition rates of 4–7 μm per minute suggest that the method may be scalable to continuous coating systems.     

Experimental analysis of the thermal annealing of hard a-C:H films

The a-C:H layers were deposited on silicon substrates in 100 kHz bipolar-pulsed discharges from a fixed mixture of acetylene and argon. Three types of a-C:H material with different hydrogen contents and hardness were obtained by adjusting the pressure during deposition to 2 Pa (hardness ≈ 23 GPa; hydrogen concentration ≈ 19 at.%), 4 Pa (20 GPa; 20 at.%) and 8 Pa (17 GPa; 24 at.%).Annealing was performed in high vacuum at a heating rate of 3 K/min up to a maximum temperature, varied between 200 °C and 900 °C. The annealing process was investigated in situ by mass spectrometric measurement of the effusion products as a function of temperature.After cooling down in high vacuum, ex situ measurements revealed changes in layer thickness (profilometer), hardness (nanoindentation), residual stress (from the curvature of the silicon substrates), elemental composition (elastic recoil detection analysis and Rutherford backscattering), UV/VIS optical properties (variable angle spectroscopic ellipsometry), and bonding (Raman spectroscopy and Fourier transform infrared spectroscopy).The films retained their hardness, level of compressive stress, and elemental composition at least up to 500 °C.The variation of the film thickness with the annealing temperature was systematically analysed. Up to 625 °C, the a-C:H thickness increased by 8.5% without measurable difference between the three layer types nor any influence of the initial a-C:H thickness. With further annealing the increase of the film thickness passed a maximum, the magnitude and temperature-position of which increased with decreasing pressure during deposition. The highest relative film thickness increase of 14% was found for a-C:H deposited at 2 Pa and annealed to 725 °C.Based on the results of the complementary characterisation methods, the effects of annealing in high vacuum on film structure and properties are discussed and fundamental processes, prevailing in characteristic annealing-temperature ranges, are derived.     

Distribution in angular mismatch between crystallites in diamond films grown in microwave plasma

High resolution electron backscattered diffraction (EBSD) has been used for analysis of grain size, texture and stress distribution on growth side of free-standing polycrystalline diamond films of different grade. The undoped and moderate boron-doped films of 0.3–0.5 mm thickness were grown by microwave plasma CVD. The highest number of stressed domains, mostly located at grain boundaries, and the largest average grain misorientation angle (θ ≈ 6°) have been found for B-doped film. Highly defected and highly [001] oriented “black” diamond exhibited much more rear stress domains, this being ascribed to angular mismatch as small as θ = 0.5° in that film. The samples of “white” diamond showed somewhat intermediate pictures, with stress observed both in bulk and on grain boundaries. Evolution of texture (columnar growth) and stress distribution with film thickness has been observed with EBSD study of film cross-sections.     

Structure and mechanical properties of oxygen doped diamond-like carbon thin films

In this study, structure and mechanical properties of doped diamond-like carbon (DLC) films with oxygen were investigated. A mixture of methane (CH₄), argon (Ar) and oxygen (O₂) was used as feeding gas, and the RF-PECVD technique was used as a deposition method. The thin films were characterized by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy (RS), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and a combination of elastic recoil detection analysis and Rutherford backscattering (ERDA-RBS). Nano-indentation tests were performed to measure hardness. Also, the residual stress of the films was calculated by Stoney equation. The XPS and ERDA-RBS results indicated that by increasing the oxygen in the feeding gas up to 5.6 vol.%, the incorporation of oxygen into the films' structure was increased. The ratio of sp² to sp³ sites was changed by the variation of oxygen content in the film structure. The sp²/sp³ ratios are 0.43 and 1.04 for un-doped and doped DLC films with 5.6 vol.% oxygen in the feeding gas, respectively. The Raman spectroscopy (RS) results showed that by increasing the oxygen content in doped DLC films, the amount of sp² CC aromatic bonds was raised and the hydrogen content reduced in the structure. The attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) confirmed the decrease of hydrogen content and the increase the ratio of CC aromatic to olefinic bonds. Hardness and residual stress of the films were raised by increasing the oxygen content within the films' structure. The maximum hardness (19.6 GPa) and residual stress (0.29 GPa) were obtained for doped DLC films, which had the maximum content of oxygen in structure, while the minimum hardness (7.1 GPa) and residual stress (0.16 GPa) were obtained for un-doped DLC films. The increase of sp³ CC bonds between clusters and the decrease of the hydrogen content, with a simultaneous increase of oxygen in the films' structure is the reason for increase of hardness and residual stress.     

Mechanical and high pressure tribological properties of nanocrystalline Ti(N,C) and amorphous C:H nanocomposite coatings

This paper reports on the mechanical and high pressure tribological properties of nanocrystalline (nc-) Ti(N,C)/amorphous (a-) C:H deposited, using low temperature (～ 200 °C) DC reactive magnetron sputtering. The mechanical properties are affected by the nc-Ti(N,C)/a-C:H phase fraction ratio. For increasing C contents (from 31 to 47 at.%) an increase of the a-C:H phase content and a degradation of the nanocrystalline phase occurs leading to a reduction in nanoindentation hardness (H) values (from 15 to 9 GPa) and reduced modulus (Er) values (from 150 to 80 GPa). A strong correlation between H/E ratio and wear performance was exhibited by the coatings. The synthesized coatings survived up to 100 m sliding distance when tested using pin-on-disc sliding configuration at > 4.5 GPa contact pressures and the measured friction coefficient values were similar for all films (μ ～ 0.21–0.25).