Multicomponent nanostructured films for various tribological applications

Many engineering materials working under severe cutting, stamping, or bearing conditions including humid and corrosive environments, as well as temperature fluctuation require a combination of chemical, mechanical, and tribological properties. For load-bearing metallic implants, the combination of excellent mechanical and tribological properties with biocompatibility and bioactivity is also of great importance. Desired properties can be achieved in hard films based on carbides, borides and nitrides of transition metals by alloying with metallic (Al, Cr, Zr) or nonmetallic (O, P, Si, Ca) elements. The present work demonstrates the potential of self-propagating high-temperature synthesis (SHS), magnetron sputtering (MS), and ion implantation assisted MS of SHS-composite targets to produce multicomponent nanostructured films with enhanced combination of properties. Three groups of recently developed films for mechanical engineering and medicine are considered: hard tribological Ti–(Al, Cr)–(Si, B, C, N) films with enhanced thermal stability, corrosion and oxidation resistance; nanocomposite and multilayered TiCrBN/WSe_x films with improved lubrication; and multifunctional bioactive nanostructured (Ti, Ta)–(Ca, Zr)–(C, N, O, Si, P) films (MuBiNaFs).     

Thermal stability of electrical properties of ZnO:Al films deposited by room temperature magnetron sputtering

In order to investigate the thermal stability of electrical properties for aluminum doped zinc oxide (ZnO:Al, AZO) films deposited by direct current reactive magnetron sputtering, AZO films deposited from an alloy target (0.8 wt.% Al) on soda-lime glasses were annealed in argon gas at different temperatures. A data capturer was applied to monitor and collect real-time sheet resistance (R_s) of the films throughout the annealing. Results revealed that R_s of the film heated at 100 °C was reduced throughout the annealing, however, conductivity of the films annealed over 100 °C was improved at early stage but then deteriorated all along to the end. Some novel R_s change points which need more penetrations were detected. The experimental results obtained from electron diffraction spectrum, X-ray diffraction pattern, X-ray photoelectron spectrum, and Hall measurement were analyzed to explore the effect of the annealing on the electrical properties of AZO films. It was found that the exotic element, which might influence the film properties, was not observed. It was also suggested that the transformation of the crystalline structure and surface chemical bonding states, which resulted in the decrease of carrier concentration and mobility could be the reason for the conductivity degeneration of the films annealed at higher temperature.     

Thermal Stability of WB2 and W-B-N Films Deposited by Magnetron Sputtering

The work is mainly to study the thermal stability including the phase stability, microstructure and tribo-mechanical properties of the AlB₂-type WB₂ and W-B-N (5.6 at.% N) films annealed in vacuum at various temperatures, which are deposited on Si and GY8 substrates by magnetron sputtering. For the WB₂ and W-B-N films deposited on Si wafers, as the annealing temperature increases from 700 to 1000 °C, a-WB (700 °C) and Mo₂B₅-type WB₂ (1000 °C) are successively observed in the AlB₂-type WB₂ films, which show many cracks at the temperature ≥?800 °C resulting in the performance failure; by contrast, only slight α-WB is observed at 1000 °C in the W-B-N films due to the stabilization effect of a-BN phase, and the hardness increases to 34.1 GPa first due to the improved crystallinity and then decreases to 31.5 GPa ascribed to the formation of α-WB. For the WB₂ and the W-B-N films deposited on WC-Co substrates, both the WB₂ and W-B-N films react with the YG8 (WC-Co) substrates leading to the formation of CoWB, CoW₂B₂ and CoW₃B₃ with the annealing temperature increasing to 900 °C; a large number of linear cracks occur on the surface of these two films annealed at ≥?800 °C leading to the film failure; after vacuum annealing at 700 °C, the friction performance of the W-B-N films is higher than that of the deposited W-B-N films, while the wear resistance of the WB₂ films shows a slight decrease compared with that of the deposited WB₂ films.     

High thermal stability of TiAlSiCN coatings with “comb” like nanocomposite structure

The aim of this work was to understand the reasons for the exceptionally high thermal stability of the TiAlSiCN coatings. The hardness of the coatings increased from 41.5 to 43 GPa between 25 and 900 °C, reached a maximum value of 49 GPa at 1000 °C, and then decreased to 37 GPa at 1300 °C. The structural investigations performed before and after annealing at 1000, 1200, and 1400 °C using X-ray diffraction, scanning and transmission electron microscopy (TEM), and high-resolution TEM showed that the as-deposited “comb” like nanocomposite structure, in which (Ti,Al)(C,N) columnar grains, 10–30 nm wide, were separated by a well developed amorphous tissue, possessed a very high thermal stability as its dominant cubic phase was stable in the temperature range of 25–1400 °C. Further thorough characterization by means of energy-dispersive spectroscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy revealed structural modifications inside crystalline and amorphous phases during annealing in vacuum. Such modifications associated with a short-range rearrangement of elements are shown to be responsible for the high hardness of the TiAlSiCN coatings observed up to 1300 °C, with peak hardness at 1000 °C.     

Thermal stability of tungsten nitride films deposited by reactive magnetron sputtering

The studies of thermal stability of nitride coatings are important since their structural, thermal, electrical and optical properties are drastically modified by the oxidation layer formed on the top of these coatings. Tungsten nitride films were deposited from metallic tungsten target using reactive pulsed d. c. magnetron sputtering. The films were annealed in air at different temperatures for 1 h. The structural, electrical resistivity and optical properties of the annealed films were analyzed. Besides the film analysis, powder of tungsten nitride was obtained by scratching the coating from the glass substrates. The oxidation kinetics of the scratched powder was studied using simultaneous thermal gravimetric/deferential thermal analysis measurements. X-ray diffraction patterns revealed that W₂N oxidizes to the two different phases WO₃ and WO_2.92. The oxide diffraction peaks appeared upon annealing at 773 K and the relative intensities increased with annealing temperature. The tungsten nitride was found to oxidize according a parabolic relation between mass gain and oxidation time. The activation energy of oxidation was evaluated by analyzing the Arrhenius relation from the temperature dependence of the weight gain. The obtained value was 1.76 eV. The activation energies of crystallization of the two phases were calculated. The electrical resistivity was found to increase drastically upon oxidation. The optical properties of the films are very sensitive to the oxidation temperature. The optical band gap values for the film oxidized at 773 K and 823 K are 2.71 and 2.58 eV, respectively.     

Thermal stability studies of atmospheric plasma deposited siloxane films deposited on Vycor™ glass

The thermal stability of siloxane films deposited on Vycor glass and silicon substrates using atmospheric pressure plasma was studied. Siloxane films were deposited from a liquid tetraethyl orthosilicate (TEOS) precursor which was nebulised into a helium/oxygen plasma. The thickness of the siloxane films was in the range 1-12 nm as measured using both ellipsometry and X-ray reflectometry. Film composition and chemical properties were examined using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis. The thermal stability of the films was evaluated under argon atmosphere at temperatures up to 700 °C. The films were found to exhibit good adhesion without cracks or delamination after the thermal treatment. A decrease in coating thickness and a reduction in surface roughness was however observed indicating, a change in coating chemistry. This was confirmed by the reduction in carbon concentration observed by XPS. Particulates generated by excess gas phase reaction of TEOS were observed on the surface of the coating. A larger reduction in particulates size was observed after thermal treatment compared with the reduction in thickness of the bulk coating. This indicates that the particulates may have a different composition to that of the coating.     

热处理温度和溅射气压对铜薄膜结构和性能影响的研究

采用射频磁控溅射镀膜法,在不同溅射气压、不同热处理温度下制备了铜薄膜,并利用扫描电镜（SEM）和X射线衍射（xRD）研究了溅射气压和热处理温度对铜薄膜结构和性能的影响。结果表明：热处理前铜薄膜的晶粒尺寸较小且大小分布不均;随着热处理温度的提高,薄膜的晶粒尺寸逐渐增大,表面更加平坦化,而晶粒之间的缝隙呈现先增大再减小后增大的趋势,在400℃时晶粒排列最紧密,表面最平坦;随着溅射气压的增高,铜（111）峰值呈现先增大后减小的趋势,当溅射气压为1．0Pa时铜的抗电迁移性最强。     

The effect of substrate bias voltage on PbTe films deposited by magnetron sputtering

The PbTe films were deposited onto ITO glass substrate by radio frequency magnetron sputtering. Effect of external direct current electrical field applied between substrate and target on the quality of films was investigated. Stylus surface profile, X-ray diffraction (XRD), atomic force microscope (AFM) and Fourier transform infrared spectroscopy (FTIR) were used to characterize the films. The film thickness was measured by a conventional stylus surface profile. The crystal structure and lattice parameters of films were determined by using XRD. The surface morphology of the films was measured by AFM. The absorption coefficients and optical band gaps of films were found from FTIR. The sheet resistance of the samples was measured with a four-point probe and the resistivity of the film was calculated. All the obtained films were highly textured with a strong (2 0 0) orientation. With increasing bias voltage to −30 V, the property of crystal structure, surface morphology and absorption coefficients and resistivity were improved. However, further increase of substrate bias leads to transformation of the property.     

Tarnishing resistance of silver–palladium thin films

Ag–Pd decorative coatings are supposed to provide better tarnishing resistance as compared to pure Ag, while keeping good optical (brightness) and mechanical properties (ductility). Palladium has a similar optical appearance as silver, and forms a thin protective oxide surface layer. Thus, a small incorporation of Pd in Ag could improve its tarnishing resistance.

Thin Ag–Pd films were deposited by magnetron co-sputtering from Pd and Ag targets. The Ar gas pressure, target power and substrate temperature were varied to modify the chemical composition of the films and optimise their properties.

The optical properties of the films were evaluated by spectroscopic ellipsometry and colorimetry. Increasing Ar gas pressure and substrate temperature results in a drastic decrease of the specular reflectivity of the films. At constant deposition conditions the reflectivity of the Ag–Pd films decreases with increasing Pd content.

The film hardness, evaluated by nanoindentation, increases with Pd content.

The tarnishing resistance of the films was evaluated by sulphidation tests. The colour change of the films due to the sulphidation was measured by colorimetry. The nature of chemical bonds of the tarnished products was evidenced by XPS. The results suggest an improvement of tarnishing resistance of the Ag–Pd films with increasing Pd content.     

Modification of polytetrafluoroethylene implants by depositing TiCaPCON films with and without stem cells

The present work is focused on the investigation of the structure and properties of TiCaPCON films deposited on the surface of polytetrafluoroethylene (PTFE) as potential bio-implant material. The films were deposited by DC magnetron sputtering of composite TiC_0.5 + Ca₃(PO₄)₂ target produced by self-propagating high-temperature synthesis (SHS). The film structure was examined using X-ray diffraction, scanning electron microscopy, and Raman spectroscopy. The films were also characterized in terms of their adhesion to the PTFE substrate, hardness, elastic modulus, elastic recovery, wettability, and friction coefficient both in physiological solution (normal saline) and Dulbecko modified Eagle medium with fetal calf serum. The biological properties of the films were evaluated by in vitro and in vivo experiments. In vitro studies showed that human fibroblasts well adhered and spread on the surface of the PTFE sample coated with TiCaPCON films. In vivo studies using rat hip and rabbit calvarial defect models demonstrated a high osseointegration potential of the TiCaPCON/PTFE implants. In vivo bone tissue regeneration using hybrid implants (adipose-derived stem cells/TiCaPCON film/PTFE porous membrane) were also reported.     

Mechanical and magnetic properties of copper dispersed ferrum films under heat treatment

The Cu-containing steels are widely used for nuclear pressure vessel materials because of their good performance under high pressure and high temperature. In this article, magnetron sputtering was used to prepare iron films with various Cu contents. The samples were annealed at temperature range of 300–500 °C, and the structural,mechanical, and magnetic properties were studied. The results show that both hardness and modulus change along with copper content and annealing temperature. The change in coercivity after annealing is similar to that of hardness. The crystal grain growth in matrix ferrum and Cu precipitation during annealing influences both the mechanical and magnetic properties.     

Thermal stability and sputtering resistance under irradiation of yttria dispersed ferrum films

Oxide dispersion strengthened (ODS) steels are considered as potential candidates for high temperature applications in fusion reactors be- cause of their excellent thermal creep behavior. In the present work, the double-target magnetron co-sputtering method was recommended to prepare yttria dispersed ferrum films. Vacuum annealing and ion irradiation were carried out to study the surface topography and structural features of the prepared yttria dispersed ferrum samples. Experiments proved that while the yttria doping ratio in the ferrum film increases, the recrystallization temperature of the film will be enhanced and the sputtering damage by Xenon ion irradiation will be lowered. The sput- tering resistance of the obtained films would be improved with the growing of grains under vacuum annealing.     

Thermal stability of Ta-Si-N nanocomposite thin films at different nitrogen flow ratios

Ta-Si-N thin films were applied as diffusion barriers for Cu interconnections or hard coatings in mechanical application. The resistivity, hardness and thermal stability were the important issues in the interconnections and hard coatings, respectively. In this paper, we investigated the relationship between the microstructures, resistivity, nanohardness and thermal stability of the Ta-Si-N thin films at different nitrogen flow ratios of 0-30% (N₂% = N₂ / (Ar + N₂) × 100%) by magnetron reactive co-sputtering. The Ta-Si-N films were annealed at 600, 750 and 900 °C at about 6 × 10⁻³ Pa for 1 h, respectively, to examine their thermal stability. The microstructures of Ta-Si-N films at low N₂% of 2-10% still retained the amorphous-like phase with nanocrystalline grains in an amorphous matrix at annealing of 600-900 °C. The nanohardness of amorphous-like Ta-Si-N film at N₂% of 3% was measured to be 15.2 GPa much higher than that of polycrystalline film of 10.1 GPa at N₂% of 20%. The average nanohardness of both films is stable up to 900 °C and varied in the range of 0.43-0.83 GPa. The resistivity of the as-deposited Ta-Si-N films increase with increasing N₂ flow rate. It is small around 220-540 μΩ cm for low N₂% of 2-10% while it increases abruptly to about 7700-43,000 μΩ cm at high N₂% of 20-30%. The best thermal stability of resistivity of Ta-Si-N film occurs at the N₂% of 2% in the range of 220 to 250 μΩ cm from RT to 900 °C.     

Thermal stability and oxidation resistance of laser clad TiVCrAlSi high entropy alloy coatings on Ti-6Al-4V alloy

TiVCrAlSi high entropy alloy coatings were deposited on Ti-6Al-4V alloy by laser cladding. SEM, XRD and EDS analyses show that, the as-clad coating is composed of (Ti,V)₅Si₃ and a BCC solid solution. After annealing at 800 °C for 24 h under vacuum, the coating is composed of (Ti,V)₅Si₃, Al₈(V,Cr)₅, and a BCC solid solution. The temperature-dependent phase equilibrium for the coating material calculated by using the CALPHAD method, indicates that above 880 °C the stable phases existing in the coating material are a BCC solid-solution and (Ti,V)₅Si₃. When the temperature is below 880 °C, the stable phases are (Ti,V)₅Si₃, Al₈(V,Cr)₅, and a BCC solid solution. In order to validate the calculation results, they were compared with TiVCrAlSi alloy samples prepared by arc melting, encapsulated in quartz tubes under vacuum, annealed at 400-1100 °C for 3 days and water-quenched. XRD analysis shows that the experimental phase composition agrees with the thermodynamic calculations. After vacuum annealing, there is a small increase of hardness for the laser clad TiVCrAlSi coating, which is due to the formation of Al₈(V,Cr)₅. The oxidation tests show that the TiVCrAlSi coating effectively improves the oxidation resistance of Ti-6Al-4V at 800 °C in air. The formation of a dense and adherent scale consisting of SiO₂, Cr₂O₃, TiO₂, Al₂O₃ and a small amount of V₂O₅ is supposed to be responsible for the observed improvement of the oxidation resistance.     

Zr-Al-N及Zr-Al-Si-N复合膜的微结构及力学性能

采用多靶反应磁控溅射技术制备不同Al含量的Zr-Al-N复合膜及不同Si含量的Zr-Al-Si-N复合膜。采用能谱仪、X射线衍射仪和显微硬度计对薄膜进行测试,研究Al含量对Zr-Al-N复合膜微结构和力学性能的影响以及Si含量对Zr-Al-Si-N复合膜微结构和力学性能的影响。结果表明,当Al含量为13.97at%时,Zr-Al-N复合膜的硬度达到最大,最大值为27.16 GPa,随着Al含量的继续增加,薄膜由B1(NaCl型面心立方结构)型结构向B1-B4(ZnS型纤锌矿结构)型双相结构转变,硬度急剧降低;当Si含量为18.79at%时,Zr-Al-Si-N复合膜的硬度达到最大,最大值为34.43 GPa,进一步增加Si含量薄膜向非晶态转化,薄膜硬度降低。     

Effect of Ru addition on the properties of Al-doped ZnO thin films prepared by radio frequency magnetron sputtering on polyethylene terephthalate substrate

The addition of ruthenium in aluminum-doped zinc oxide transparent conducting thin films was deposited on polyethylene terephthalate at 20 °C by radio frequency magnetron sputtering technique. The structure and electrical properties of the films were investigated with respect to variation of Ru concentration. The XRD and FESEM results show that the film with 0.5 wt% Ru doping has the best crystallinity and larger pyramid-like grains, therefore the resistivity reached to a lowest value of 9.1 × 10⁻⁴ Ωcm. The low carrier mobilities of the films (3–7.2 cm² V⁻¹ s⁻¹), however, were limited by ionized impurity scattering and grain boundary scattering mechanisms since the carrier concentrations were ranged from 2.2 × 10²⁰ to 9.5 × 10²⁰ cm⁻³. The transmittance in the visible is greater than 80% with the optical band gap in the order of 3.352–3.391 eV.     

Influence of carbon sputtering power on structure, corrosion resistance, adhesion strength and wear resistance of platinum/ruthenium/nitrogen doped diamond-like carbon thin films

Platinum/ruthenium/nitrogen doped diamond-like carbon (PtRuN-DLC) thin films were deposited on conductive p-Si substrates using a DC magnetron sputtering deposition system by varying carbon sputtering power. The chemical composition, bonding structure, surface morphology and adhesion strength of the PtRuN-DLC films were investigated using X-ray photoelectron spectroscopy (XPS), micro-Raman spectroscopy, atomic force microscopy (AFM), and micro-scratch test, respectively. The corrosion behavior of the PtRuN-DLC films in a 0.1 M NaCl solution was investigated using potentiodynamic polarization test. The corrosion results indicated that the corrosion resistance of the PtRuN-DLC films increased with increased carbon sputtering power probably due to decreased porosity level in the films with increased growth rate and film thickness. The wear performance of the PtRuN-DLC films was investigated with a ball-on-disc micro-tribometer. It was found that the increased carbon sputtering power significantly improved the wear performance of the films by enhancing the adhesion strength of the films.     

Characterization of magnetron sputtering TiB2 and Ti-B-N thin films

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Ta-doped multifunctional bioactive nanostructured films

Ta-doped multifunctional bioactive nanostructured films (MuBiNaFs) were deposited by DC magnetron sputtering or ion implantation assisted magnetron sputtering of composite (Ti,Ta)C + Ca₃(PO₄)₂ and (Ti,Ta)C + CaO targets produced by self-propagating high-temperature synthesis method. The films were characterized in terms of their structure, elemental and phase composition using X-ray diffraction, transmission electron microscopy, X-ray photoelectron, Raman, and IR spectroscopy. The films deposited in an Ar atmosphere consisted of (Ti,Ta)C, Ti_xO_y, and CaO phases in an amorphous matrix with P-O, C-O, and O-H bonding. In the films deposited in a gaseous mixture of Ar + 14%N₂, apart from the (Ti,Ta)(C,N), Ti_xO_y, and CaO phases, the indication of diamond-like carbon, bcc Ta and traces of P-O bonding were observed. The MuBiNaFs demonstrated high hardness in the range of 38-44  GPa, Young's modulus 310-350  GPa, high percentage of elastic recovery 70-75%, low friction coefficient down to 0.17-0.25 (both in air and under physiological solution) and two orders of magnitude lower wear rate compared with Ti substrate. Ti ion implantation of growing films was shown to be an effective instrument to decrease their high internal stress. Static water contact angle measurements indicated hydrophilic nature of film surfaces. The electrochemical tests demonstrated that the Ta-doped films had positive values of corrosion potential with low current density. In vitro studies showed that cultured IAR-2 epitheliocytes and MC3T3-E1 osteoblastic cells were well spread on the surface of films and their actin cytoskeleton was well organized. Osteoblastic cells had a high rate of proliferation on all examined films and expressed alkaline phosphatase activity, an early-stage differentiation marker. The MuBiNaF revealed a high level of biocompatibility and biostability at experiments in vivo.     

Growth, stress and hardness of reactively sputtered tungsten nitride thin films

Tungsten nitride (WN_x) thin films were deposited on Si(100) substrates using direct current reactive magnetron sputtering in discharging a mixture of N₂ and Ar gas. The effects of nitrogen flow rate (F_N2) and substrate bias voltage (V_b) on the composition, phase structure, and mechanical properties for the obtained films were evaluated by means of X-ray photoelectron spectroscopy, X-ray diffraction, high-resolution transmission electron microscopy and nanoindentation. The evolution of phase structure is found closely correlated to N concentration in the films. When V_b = −40 V, with increasing F_N2, the N/W atomic ratio gradually increases in the film, accompanied by a phase transition from cubic β-W to hexagonal WN through face centered-cubic (fcc)-W₂N. At F_N2 = 15 sccm, the N/W atomic ratio gradually decreases with increasing the absolute value of V_b, resulting in a transition from fcc-W₂N to cubic β-W(N) through a mixture of fcc-W₂N + β-W(N). In addition, the increase in implanted nitrogen causes the increase in the compressive stress with increasing F_N2. In contrast, although with increasing the absolute value of V_b from 80 to 160 V the N/W atomic ratio decreases, the increase of the defects caused by increasing ion bombarding energy, dominates the increase of the compressive stress. Furthermore, the maximum hardness value for the films arrives at 38.9 GPa, which is obtained at V_b = −120 V when fcc-W₂N + β-W(N) mixed structure is formed.