Effects of substrate bias on the structure and mechanical properties of (Al1.5CrNb0.5Si0.5Ti)Nx coatings

(Al_1.5CrNb_0.5Si_0.5Ti)N_x high-entropy nitride coatings were designed and investigated in this study. Nitride coatings are deposited under a sufficient amount of nitrogen at 415 °C on Si by direct current magnetron reactive sputtering from a non-equimolar Al_1.5CrNb_0.5Si_0.5Ti high-entropy alloy target. The effects of substrate bias (V_s) on film structure and mechanical properties are studied. All these coatings have a single NaCl-type face-centered cubic structure and nearly stoichiometric ratio of (Al_1.5CrNb_0.5Si_0.5Ti)₅₀ N₅₀. A distinct refinement of microstructure of the films is observed when V_s varies from 0 V to − 100 V. Typical columnar structure transits into a dense and featureless structure and grain size decreases from 70 nm to 5 nm. Similar refinement remains at larger bias(− 150 or − 200 V). At the same time, the residual compressive stress increases from near zero to − 3.9 GPa at − 150 V and then decreases to − 3.2 GPa at − 200 V. The hardness increases from 12 GPa at 0 V, peaks at 36 GPa at − 100 V, and then decreases to 26 GPa at − 200 V. The structural evolution strengthening mechanism are discussed and compared with equimolar high-entropy nitrides.     

Evolution of structure and properties of multi-component (AlCrTaTiZr)Ox films

(AlCrTaTiZr)O_x films were deposited at 350 °C by DC magnetron sputtering from high-entropy alloy target. Oxygen concentration increases with oxygen flow ratio, and saturates near 67 at.%. As-deposited films have an amorphous structure. Their hardness fall in the range of 8-13 GPa. All amorphous oxide films maintain their amorphous structure up to 800 °C for at least 1 h. After 900 °C 5 h annealing, crystalline phases with the structures of ZrO₂, TiO₂, or Ti₂ZrO₆ form. Annealing enhances mechanical properties of the films. Their hardness and modulus attain to the values about 20 and 260 GPa, respectively. The resistivity of the metallic films is around 10² μΩ cm but drastically rises to 10¹² μΩ cm when oxygen concentration increases.     

Tribology of ultra high molecular weight polyethylene film on Si substrate with chromium nitride, titanium nitride and diamond like carbon as intermediate layers

This paper presents tribological studies on composite films consisting of different intermediate hard layers (chromium nitride (CrN), titanium nitride (TiN) and diamond like carbon (DLC)) on Si substrate followed by soft ultra high molecular weight polyethylene (4-5 μm thick) as the top layer. The tribological properties of the composite films were evaluated on a ball-on-disc tribometer (composite film sliding against a 4 mm diameter Si₃N₄ ball) at a normal load of 40 mN and a linear speed of 0.052 m/s. The wear durability of the composite films increases with increasing hardness of the intermediate layers. The composite film with harder intermediate layers (TiN with 24 GPa and DLC layers with 57 GPa and 70 GPa of hardness) provides the best tribological performance with more than 300,000 cycles of sliding when the experiments were stopped. The critical loads of scratching correlate with the wear performances of the composite films. Application of only a few nanometer overcoat of perfluoropolyether on the most wear resistant composite films can further increase the wear lives (more than one million cycles) even at a higher normal load of 70 mN.     

Characterization of SiNx:H films deposited by rapid thermal chemical vapor deposition

Hydrogenated silicon nitride films were deposited with NH₃, SiH₄ and N₂ gas mixture at 700 °C by rapid thermal chemical vapor deposition (RTCVD) system. The NH₃/N₂ flow ratio and deposition pressure are found to influence the film properties. The stress of SiN_x:H films deposited by RTCVD is tensile, which can reach ~ 1.5 GPa in our study. The stress of SiN_x:H films is dependent on the deposition parameters, which can be associated with chemical configuration of the film. It is suggested that the presence of hydrogen atoms will relax the Si-N network, which results in the decrease of tensile stress of the SiN_x:H film.     

Influence of RF power on the electrical and mechanical properties of nano-structured carbon nitride thin films deposited by RF magnetron sputtering

Nano structured carbon nitride thin films were deposited at different RF powers in the range of 50 W to 225 W and constant gas ratio of (argon: nitrogen) Ar:N₂ by RF magnetron sputtering. The atomic percentage of Nitrogen: Carbon (N/C) content and impedance of the films increased from 14.36% to 22.31% and 9 × 10⁻¹ Ω to 7 × 10⁵ Ω respectively with increase in RF power. The hardness of the deposited films increased from 3.12 GPa to 13.12 GPa. The increase in sp³ hybridized C-N sites and decrease of grain size with increase in RF power is responsible for such variation of observed mechanical and electrical properties.     

Study on adhesion and wear resistance of multi-element (AlCrTaTiZr)N coatings

Multi-element (AlCrTaTiZr)N films were deposited on cemented carbide and M2 steel substrates by reactive RF magnetron sputtering. Prior to nitride film deposition, an interlayer between the film and the substrate was introduced to improve adhesion property. The influence of interlayer materials (Ti, Cr, and AlCrTaTiZr alloy) and interlayer thickness (0–400 nm) on the adhesion and tribological properties of films was investigated. In this study, the nitride film deposited at R_N = 20% exhibited the highest hardness (35.2 GPa) and the lowest residual compressive stress (? 1.52 GPa), and was prepared as the top layer for further testing. The interlayer materials can effectively improved the film adhesion onto the cemented carbide substrates, and the adhesive failure was not observed even under the normal load of 100 N. For M2 steel substrates, only the Cr interlayer can slightly improve the film adhesion, and the cohesive and adhesive failure can be found at relatively lower applied load. The optimal interlayer thickness was 100–200 nm for the 1 µm-thick (AlCrTaTiZr)N film and can be related to the stress evolution. The friction coefficient and wear rate for the (AlCrTaTiZr)N film were 0.82 and 4.9 × 10^? 6 mm³/Nm, respectively, and almost kept constant under different interlayer materials and thickness. The worn-through event of the nitride film during tribological test occurred easily owing to its poor adhesion behavior, and can be improved by interlayer additions.     

Influence of N2 flow rate on the mechanical properties of SiNx films deposited by microwave electron cyclotron resonance magnetron sputtering

Hydrogen-free amorphous silicon nitride (SiN_x) films were deposited at room temperature by microwave electron cyclotron resonance plasma-enhanced unbalance magnetron sputtering. Varying the N₂ flow rate, SiN_x films with different properties were obtained. Characterization by Fourier-transform infrared spectrometry revealed the presence of Si-N and Si-O bonds in the films. Growth rates from 1.0 to 4.8 nm/min were determined by surface profiler. Optical emission spectroscopy showed the N element in plasma mainly existed as N⁺ species and N₂⁺ species with 2 and 20 sccm N₂ flow rate, respectively. With these results, the chemical composition and the mechanical properties of SiN_x films strongly depended on the state of N element in plasma, which in turn was controlled by N₂ flow rate. Finally, the film deposited with 2 sccm N₂ flow rate showed no visible marks after immersed in etchant [6.7% Ce(NH₄)₂(NO₃)₆ and 93.3% H₂O by weight] for 22 h and wear test for 20 min, respectively.     

Effect of bias voltage on microstructure, mechanical and wear properties of Al-Si-N coatings deposited by cathodic arc evaporation

Al-Si-N coatings were deposited on tungsten carbide (WC-Co) and silicon wafer substrates using Cr and AlSi (12 at.% Si) alloy targets using a dual cathode source with short straight-duct filter in the cathode arc evaporation system. Al-Si-N coatings were synthesized under a constant flow of nitrogen, using various substrate bias voltages at a fixed AlSi cathode power. To enhance adhesive strength, the Cr/(Cr_xAl_ySi_z)N graduated layer between the top coating and the substrate was deposited as a buffer interlayer. The effects of bias voltage on the microstructure, mechanical and wear properties of the Al-Si-N films were investigated. Experimental results reveal that the Al-Si-N coatings exhibited a nanocomposite structure of nano-crystalline h-AlN, amorphous Si₃N₄ and a small amount of free Si and oxides. It was also observed that the deposition rate of as-deposited films gradually decreased from about 25.1 to 18.8 nm/min when the substrate bias was changed from − 30 to − 150 V. The XRD results revealed that h-AlN preferred orientation changed from (002) to (100) as the bias voltage increased. The maximum hardness of approximately 35 GPa was obtained at the bias voltage of −90 V. Moreover, the grain size was inversely proportional to the hardness of the film. Wear test results reveal that the Al-Si-N film had a lower coefficient of friction, between 0.5 and 0.7, than that 0.7 of the AlN film.     

Mechanical properties optimization of tungsten nitride thin films grown by reactive sputtering and laser ablation

Transition metal nitrides coatings are used as protective coatings against wear and corrosion. Their mechanical properties can be tailored by tuning the nitrogen content during film synthesis. The relationship between thin film preparation conditions and mechanical properties for tungsten nitride films is not as well understood as other transition metal nitrides, like titanium nitride. We report the synthesis of tungsten nitride films grown by reactive sputtering and laser ablation in the ambient of N₂ or N₂/Ar mixture at various pressures on stainless steel substrates at 400  C. The composition of the films was determined by XPS. The optimal mechanical properties were found by nanoindentation based on the determination of the proper deposition conditions. As nitrogen pressure was increased during processing, the stoichiometry and hardness changed from W₉N to W₄N and 30.8-38.7 GPa, respectively, for films deposited by reactive sputtering, and from W₆N to W₂N and 19.5-27.7 GPa, respectively, for those deposited by laser ablation.     

Preparation of various DLC films by T-shaped filtered arc deposition and the effect of heat treatment on film properties

Different types of diamond-like carbon (DLC) films (ta-C, a-C, ta-C:H and a-C:H) were prepared on super hard alloy (WC-Co) substrate using a T-shape filtered arc deposition (T-FAD) system. At first, the film properties, such as structure, hydrogen content, density, hardness, elastic modulus, were measured. Ta-C prepared with a DC bias of −100 V showed the highest density (3.1 g/cm³) and hardness (70-80 GPa), and the lowest hydrogen content (less than 0.1 at. %). It was found that the hardness of the DLC film is proportional to approximately the third power of film density. The DLC films were then heated for 60 min in an electric furnace at 550 °C in N₂. Only the ta-C film hardly change its structure, although other films were graphitized. The 200-nm thick ta-C film was then heated for 60 min through the temperature range from 400 to 800 °C in N₂ with 2 vol.% of O₂ and the film structure found to be stable up to 700 °C. The substrate was oxidized at 800 °C, indicating the ta-C film had a thermal barrier function up to that temperature.     

Synthesis and characterization of Cu3N-WC nanocomposite films prepared by direct current magnetron sputtering

Cu₃N-WC films were synthesized on an arc ion plated TiN_x interlayer by direct current magnetron sputtering. The Cu₃N-WC films, composed of columnar WC crystals 3-5 nm in size and amorphous Cu₃N phases, were grown using the layer-plus-island mode. Deposition rate of Cu₃N-WC films declined from 11.7 to 7.5 nm/min when the WC target power increased from 200 to 400 W because the Cu target was poisoned by the diffusion of WC molecules. Nano-indentation testing results showed that the highest measure of hardness of Cu₃N-WC films was up to ∼ 41 GPa and the H³/E^?2 value of the Cu₃N-WC_47.4 was around 0.41 GPa, indicating the excellent plastic deformation resistance of the film. Incorporation of the soft lubricant Cu₃N phase and the uniform distribution of WC hard phases resulted in significant improvements in friction coefficient and wear resistance. As such, Cu₃N-WC films have a good potential in future wear applications.     

Tribological and mechanical behaviors of TiN/CNx multilayer films deposited by magnetron sputtering

TiN/CN_x multilayer films with bilayer periods of 4.5-40.3 nm were deposited by direct-current magnetron sputtering. Layer morphology and structure of the multilayered films were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy. The TiN/CN_x multilayers exhibited coherent epitaxial growth due to the mutual growth-promoting effect at small bilayer period and some crystalline regions going through the interface of TiN/CN_x. Nanoindentation tests showed that the hardness of the multilayers varied from 12.5 to 31 GPa, with the highest hardness being obtained with a bilayer period of 4.5 nm. The tribological properties of the films were investigated using a ball-on-disk tribometer in humid air, and the TiN/CN_x multilayer with a bilayer period of 4.5 nm also exhibited the lowest friction coefficient and the highest wear resistance.     

Microstructures and mechanical properties of multi-component (AlCrTaTiZr)NxCy nanocomposite coatings

Multi-component (AlCrTaTiZr)N_xC_y coatings with the incorporation of quinary metallic elements and different N and C contents were deposited by AlCrTaTiZr/C co-sputtering in an N₂/Ar mixed atmosphere under an AlCrTaTiZr-alloy-target power of 150 W and different C-target powers (0-200 W). At a C-target power of 0 W, an (AlCrTaTiZr)N_0.6 coating with a face-centered cubic solid-solution structure was deposited and exhibited a large columnar structure; its hardness and steady-stage creep strain rate were measured as about 20 GPa and 1.5 × 10⁻⁴ 1/s, respectively. By applying a C-target power of 100 W, an (AlCrTaTiZr)N_0.6C_0.2 coating was formed with a fine columnar structure. Owing to the incorporated C atoms, the (111) interplanar spacing of the face-centered cubic structure was increased from 0.249 to 0.253 nm. The hardness increased to 32 GPa and the creep strain rate was lowered to 1.1 × 10⁻⁴ 1/s attributed to the introduction of covalent-like bonds, grain refinement and the formation of an amorphous-like and nanocomposite structure. Furthermore, under a C-target power of 200 W, excess C atoms agglomerated to form clusters in the deposited (AlCrTaTiZr)N_0.6C_0.4 coating. Consequently, the hardness slightly decreased to 30 GPa and the creep strain rate increased to 2.4 × 10⁻⁴ 1/s.     

Synthesis of Al-Cr-O-N thin films in corundum and f.c.c. structure by reactive r.f. magnetron sputtering

Advanced PVD coatings for metal cutting applications must exhibit a multifunctional property profile including high hardness, chemical inertness and high temperature stability. Recently, ternary Al-Cr-O thin films with mechanical properties similar or superior to conventional aluminium oxide thin films have been suggested as potential materials meeting such demands. These coatings can be deposited at moderate temperatures in PVD processes. In this work, new quaternary Al-Cr-O-N coatings are suggested as alternative for offering thin film materials of high strength, hardness and even toughness. A combinatorial approach to the synthesis of Al-Cr-O-N thin films by means of reactive r.f. magnetron sputtering is presented. A thorough phase analysis of deposited coatings covering a wide range of elemental compositions revealed a well-defined phase transition from a corundum-type α-(Al_1 − x,Cr_x)_2 + δ(O_1 − y,N_y)₃ structure to a CrN-type f.c.c.-(Al_1 − x,Cr_x)_1 + θ(O_1 − y,N_y) structure as a function of the Al/Cr ratio and the nitrogen gas flow ratio. Detailed results on the coatings composition, constitution and microstructure are discussed compared to ternary Al-Cr-O thin films deposited by reactive r.f. magnetron sputtering under nearly identical conditions.     

Nanomechanical properties of FePtPd ternary alloy thin films

Presented in this study are crystalline structure and mechanical properties of FePt_0.75Pd_0.25 ternary alloy thin films deposited under the various annealing temperatures, obtained by means of transmission electron microscopy (TEM) and nanoindentation techniques. FePtPd ternary alloy thin films are deposited on Si substrates using a multi-target DC magnetron sputtering system. Results indicate that the grain size increase from 40 to 135 nm as the annealing temperature increases from 400 to 600 °C. From nanoindentation measurements, the hardness of FePtPd ternary alloy thin films are 11.6 ± 0.4, 10.4 ± 0.1 and 8.8 ± 0.3 GPa for the annealed temperatures of 400, 500 and 600 °C, respectively. And, the corresponding Young's moduli are 175.4, 152.2 and 142.6 GPa, respectively. Hardness for FePtPd ternary alloy thin films decreased slightly in accordance with the increase of the grain size. By fitting experimental results with the Hall-Petch equation, a probable lattice friction stress of 5.15 ± 0.05 GPa and Hall-Petch constant of 44.25 ± 2.55 GPa nm^1/2 are obtained.     

Effect of NH3 flow rate on growth, structure and luminescence of amorphous silicon nitride films by electron cyclotron resonance plasma

In this paper, hydrogenated amorphous silicon nitride (a-SiN_x:H) films have been deposited using an electron cyclotron resonance chemical vapor deposition system. The effect of NH₃ flow rate R on the deposition rate, structure and luminescence were studied using various techniques such as optical emission spectroscopy, Fourier Transform Infrared absorption (FTIR), X-ray photoelectron spectroscopy (XPS) and fluoro-spectroscopy, respectively. Optical emission behavior of SiH₄ + NH₃ plasma shows that atomic Si radical concentration determines the film deposition rate. Structural transition of a-SiN_x film from Si-rich one to near-stoichiometric/N-rich one with R was revealed by FTIR and the two phase separation of a-Si and a-Si₃N₄ was also convinced in Si-rich SiN_x films by XPS. Either photo- or electroluminescence for all the SiN_x films with R > 3 sccm shows a strong light emission in visible light wavelength range. As R < 6 sccm, recombination of electrons and holes in a-Si quantum dots is the main mechanism of photo/electroluminescence for Si-rich SiN_x films, however, for photoluminescence, gap states' luminescence is also in competition; as R > 6 sccm, light emission of the SiN_x film originates from defect states in its band gap.     

Microstructure evolution and age hardening in (Ti,Si)(C,N) thin films deposited by cathodic arc evaporation

Ti_1 − xSi_xC_yN_1 − y films have been deposited by reactive cathodic arc evaporation onto cemented carbide substrates. The films were characterized by X-ray diffraction, elastic recoil detection analysis, transmission electron microscopy, energy-dispersive X-ray spectroscopy, electron-energy loss spectroscopy and nanoindentation. Reactive arc evaporation in a mixed CH₄ and N₂ gas gave films with 0 ≤ x ≤ 0.13 and 0 ≤ y ≤ 0.27. All films had the NaCl-structure with a dense columnar microstructure, containing a featherlike pattern of nanocrystalline grains for high Si and C contents. The film hardness was 32-40 GPa. Films with x > 0 and y > 0 exhibited age-hardening up to 35-44 GPa when isothermally annealed up to 900 °C. The temperature threshold for over-ageing was decreased to 700 °C with increasing C and Si content, due to migration of Co, W and Cr from the substrate to the film, and loss of Si. The diffusion pathway was tied to grain boundaries provided by the featherlike substructure.     

Bulge testing and fracture properties of plasma-enhanced chemical vapor deposited silicon nitride thin films

The mechanical properties and fracture behavior of silicon nitride (SiN_x) thin film fabricated by plasma-enhanced chemical vapor deposition is reported. Plane-strain moduli, prestresses, and fracture strengths of silicon nitride thin films deposited both on a bare Si substrate and on a thermally oxidized Si substrate were extracted using bulge testing combined with a refined load-deflection model of long rectangular membranes. The plane-strain moduli and prestresses of SiN_x thin films have little dependence on the substrates, that is, for the bare Si substrate, they are 133 ± 19 GPa and 178 ± 22 MPa, respectively, while for the thermally oxidized substrate, they are 140 ± 26 GPa and 194 ± 34 MPa, respectively. However, the fracture strength values of SiN_x films grown on the two substrates are quite different, i.e., 1.53 ± 0.33 GPa and 3.08 ± 0.79 GPa for the bare Si substrate and the oxidized Si substrate, respectively. The reference stresses were computed by integrating the local stress of the membrane at the fracture over the edge, surface, and volume of the specimens and fitted with the Weibull distribution function. For SiN_x thin film produced on the bare Si substrate, the volume integration gave a significantly better agreement between data and model, implying that the volume flaws are the dominant fracture origin. For SiN_x thin film grown on the oxidized Si substrate, the fit quality of surface and edge integration was significantly better than the volume integration, and the dominant surface and edge flaws could be caused by buffered HF attacking the SiN_x layer during SiO₂ removal.     

A study of the nanostructure and hardness of electron beam evaporated TiAlBN Coatings

TiAlBN coatings have been deposited by electron beam (EB) evaporation from a single TiAlBN material source onto AISI 316 stainless steel substrates at a temperature of 450 °C and substrate bias of − 100 V. The stoichiometry and nanostructure have been studied by X-ray photoelectron spectroscopy, X-ray diffraction and transmission electron microscopy. The hardness and elastic modulus were determined by nanoindentation. Five coatings have been deposited, three from hot-pressed TiAlBN material and two from hot isostatically pressed (HIPped) material. The coatings deposited from the hot-pressed material exhibited a nanocomposite nc-(Ti,Al)N/a-BN/a-(Ti,Al)B₂ structure, the relative phase fraction being consistent with that predicted by the equilibrium Ti-B-N phase diagram. Nanoindentation hardness values were in the range of 22 to 32 GPa. Using the HIPped material, coating (Ti,Al)B_0.29N_0.46 was found to have a phase composition of 72-79 mol.% nc-(Ti,Al)(N,B)_1 − x+ 21-28 mol.% amorphous titanium boride and a hardness of 32 GPa. The second coating, (Ti,Al)B_0.66N_0.25, was X-ray amorphous with a nitride+boride multiphase composition and a hardness of 26 GPa. The nanostructure and structure-property relationships of all coatings are discussed in detail. Comparisons are made between the single-EB coatings deposited in this work and previously deposited twin-EB coatings. Twin-EB deposition gives rise to lower adatom mobilities, leading to (111) (Ti,Al)N preferential orientation, smaller grain sizes, less dense coatings and lower hardnesses.     

Structure, mechanical and tribological properties of diamond-like carbon films on aluminum alloy by arc ion plating

The low hardness and poor tribological performance of aluminum alloys restrict their engineering applications. However, protective hard films deposited on aluminum alloys are believed to be effective for overcoming their poor wear properties. In this paper, diamond-like carbon (DLC) films as hard protective film were deposited on 2024 aluminum alloy by arc ion plating. The dependence of the chemical state and microstructure of the films on substrate bias voltage was analyzed by X-ray photoelectron spectroscopy and Raman spectroscopy. The mechanical and tribological properties of the DLC films deposited on aluminum alloy were investigated by nanoindentation and ball-on-disk tribotester, respectively. The results show that the deposited DLC films were very well-adhered to the aluminum alloy substrate, with no cracks or delamination being observed. A maximum sp³ content of about 37% was obtained at −100 V substrate bias, resulting in a hardness of 30 GPa and elastic modulus of 280 GPa. Thus, the surface hardness and wear resistance of 2024 aluminum alloy can be significantly improved by applying a protective DLC film coating. The DLC-coated aluminum alloy showed a stable and relatively low friction coefficient, as well as narrower and shallower wear tracks in comparison with the uncoated aluminum alloy.