Oxidation study of Cr-Ru hard coatings

Cr-Ru alloy coatings with Cr content ranging from 47 to 83 at.% were deposited at 400 °C by direct current magnetron co-sputtering with a Ti interlayer on silicon substrates. With a total input power of 300 W, the Cr content in the Cr-Ru coatings increased linearly with the increasing input power of Cr. The intermetallic compound phase Cr₂Ru with columnar structure was identified for the as-deposited Cr₅₆Ru₄₄ and Cr₆₅Ru₃₅ coatings, resulting in an increase of hardness up to 15-16 GPa. To evaluate the performance of Cr-Ru coatings as a protective coating on glass molding dies, the annealing treatment was conducted at 600 °C in a 50 ppm O₂-N₂ atmosphere. The outward diffusion and preferential oxidization of Cr in the Cr-Ru coatings resulted in the variations of the crystalline structure, chemical composition distribution, and surface hardness after annealing. X-ray diffraction and transmission electron microscopy (TEM) proved that an oxide scale consisting of Cr₂O₃ formed on the free surface. Scanning electron microscopy and TEM observed the surface morphology and structural variation. The chemical composition depth profiles were analyzed by Auger electron microscopy, verifying the presence of a Cr-depleted zone beneath the oxide scale. The hardness of Cr₅₆Ru₄₄ and Cr₆₅Ru₃₅ coatings decreased to 11-12 GPa after annealing, accompanied by the replacement of the Cr₂Ru phase by the Ru phase.     

Characterization of nano-structured W-, Ti-, V-, and Zr-doped carbon films

Bonding structure of carbon and metal as well as nanostructural changes of metal-doped amorphous carbon films (a-C:Me) were investigated depending on metal type (W, Ti, V, and Zr), concentration (<25 at.%) and annealing temperature (< 1300 K, except W: < 2800 K). Pure C films exhibit ~ 2 nm distorted aromatic and graphene-like regions. Both increase in size with annealing. After deposition the metals have carbide-like bonding and are mainly distributed atomically disperse in an amorphous environment. Annealing leads to the formation of carbide crystallites (TiC, VC, ZrC, WC, W₂C, and WC_1 − x) of several nanometers. The VC particles reach the largest size up to 1300 K. All metal dopings reduce the erosion rate against oxidation (expect V) and hydrogen impact.     

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.     

Micro-hardness, microstructures and thermal stability of (Ti,Cr,Al,Si)N films deposited by cathodic arc method

(Ti,Cr,Al,Si)N films were deposited by cathodic arc method using TiCrAlSi alloy cathodes. It was found that the microstructures of (Ti,Cr,Al,Si)N were closely related to (Al+Si) content. The crystal structure of (Ti,Cr,Al,Si)N was NaCl-type structure up to the (Al+Si) content of 0.60, where it changed to a hexagonal structure. The maximum hardness of 33 GPa was obtained at the lowest (Al+Si) content of 0.56, still in the cubic structure. The micro-hardness decreased down to 28 GPa as the crystal structure changed from NaCl-type to wurtzite-type.To investigate the thermal stabilities of (Ti,Cr,Al,Si)N, the films were annealed in a vacuum furnace. In Ti_0.20Cr_0.20Al_0.55Si_0.05N with cubic structure, the phase segregation occurred by annealing at over 900 °C, while Ti_0.22Cr_0.22Al_0.44Si_0.12N remained in cubic phase up to 1000 °C. The micro-hardness of Ti_0.20Cr_0.20Al_0.55Si_0.05N increased and that of Ti_0.22Cr_0.22Al_0.44Si_0.12N decreased at 1000 °C. Ti_0.20Cr_0.11Al_0.58Si_0.11N with a cubic and hexagonal mixture phase held its (c,h)-mixture phase up to 1000 °C, while there was an indication of an increase both in micro-hardness and in cubic ratio after annealing.In this paper, the micro-hardness and microstructure of (Ti,Cr,Al,Si)N are discussed as a function of annealing temperature and investigated by X-ray diffraction and electron microscopy.     

Annealing of sputter-deposited nanocrystalline Cr-Ta coatings in a low-oxygen-containing atmosphere

As a protective hard coating on glass molding dies, Cr-Ta coatings were fabricated on binderless tungsten carbide substrates with a Ti interlayer by RF magnetron sputtering. The nanocrystalline Cr-Ta coatings were deposited at 550 °C, which revealed one nanocrystalline phase for the Ta-rich coating and two nanocrystalline phases for the Cr-rich coating. Annealing treatment was conducted at 600 °C in a 12 ppm O₂-N₂ atmosphere to evaluate the coating performance in a realistic glass molding environment. Both Auger electron spectroscopy and X-ray photoelectron spectroscopy depth profiles verified the outward diffusion of Cr, which formed a protective coating for the Cr-rich coatings. A scale of Cr₂O₃ and a Cr-depleted transition zone near the surface were identified by conducting a transmission electron microscopy investigation on the annealed Cr_0.71Ta_0.29 coating. The Cr-rich coating absorbed a smaller amount of oxygen, exhibited greater hardness, and maintained nanoscale surface roughness after annealing in the glass molding atmosphere, thus making it an appropriate protective coating for the die material.     

Electrical properties of vanadium tungsten oxide thin films

The vanadium tungsten oxide thin films deposited on Pt/Ti/SiO₂/Si substrates by RF sputtering exhibited good TCR and dielectric properties. The dependence of crystallization and electrical properties are related to the grain size of V_1.85W_0.15O₅ thin films with different annealing temperatures. It was found that the dielectric properties and TCR properties of V_1.85W_0.15O₅ thin films were strongly dependent upon the annealing temperature. The dielectric constants of the V_1.85W_0.15O₅ thin films annealed at 400 °C were 44, with a dielectric loss of 0.83%. The TCR values of the V_1.85W_0.15O₅ thin films annealed at 400 °C were about −3.45%/K.     

Internal oxidation mechanism for Ta-Ru and Mo-Ru coatings

Ta-Ru and Mo-Ru alloy coatings with phases of intermetallic compounds are often used as protective coatings on die materials. After annealing under an oxygen containing atmosphere, the internal oxidation phenomenon resulted in the preferential oxidation of Ta or Mo in the coatings. This process created a phase separated structure consisting of continuous and alternative oxygen rich and deficient layers with a nano scale period beneath the free surface. The experiments in this study deposited Ta-Ru and Mo-Ru coatings with a Cr interlayer by direct current magnetron co-sputtering at 400 °C. Annealing treatments were conducted at 600 °C for short durations under controlled atmospheres consisting of 50 or 10,000 ppm oxygen with residual nitrogen or argon gas. The internal oxidation behavior in the initial stage was determined by evaluating the variations in crystalline structure, surface morphology and chemical composition. The laminated structure was examined by transmission electron microscopy. Results show distinct oxidation behaviors for Ta₄₇Ru₅₃ and Mo₄₆Ru₅₄ coatings. Internal oxidation phenomena appeared in Ta₄₇Ru₅₃ coatings annealed in both 50 and 10,000 ppm O₂ containing atmospheres. The Mo₄₆Ru₅₄ coatings exhibit external oxidation at 50 ppm O₂ containing atmosphere, and internal oxidation at 10,000 ppm O₂ containing atmosphere. Finally, this study proposes an internal oxidation mechanism for alloy coatings with an orientated structure.     

Titanium and zirconium hard coatings on glass substrates prepared by the sol-gel method

In this work innovative antiscratch sol-gel coating films deposited on a soda-lime glass substrate are examined. Sol-gel coatings of different composition (TiO₂, TiO₂/B₂O₃, ZrO₂ and ZrO₂/B₂O₃) were prepared starting from Titanium, Zirconium and Boron alkoxides and from boron oxide. Coatings were obtained at room temperature and at atmospheric pressure by dip-coating using common soda lime silicate glass slides as substrates. Densification was carried out at 550 °C for 2 h in air. The morphology of the coatings has been studied by Atomic Force Microscopy, Scanning Electron Microscopy, and with a profilometer. Roughness grows with thickness and with boron addition. The mechanical properties of the films were evaluated by micro scratch at fixed and variable load. The scratch hardness numbers of ZrO₂ and ZrO₂/B₂O₃ coatings reach 6 GPa (glass value = 1.9 GPa), whereas the best value for the critical load is 16.7 N (glass value = 9 N).     

Characterization of magnetron co-sputtered W-doped C-based films

In this paper, W-doped C-based coatings were deposited on steel and silicon substrates by RF magnetron sputtering, using W and C targets, varying the cathode power applied to the W target and the substrate bias. The chemical composition was varied by placing the substrates in a row facing the C and W targets. W content in the films increased from 1 to 2 at.% over the C target to ∼ 73 at.% over the W target. The coatings with W content lower than ∼ 12 at.% and ∼ 23 at.%, for biased and unbiased conditions, respectively, showed X-ray amorphous structures, although carbide nanocrystals must exist as shown by the detection of the WC_1−x phase in films with higher W content. C-rich films were very dense and developed a columnar morphology with increasing W content. An improvement in the hardness (from 10 GPa, up to 25 GPa) of the films was achieved either when negative substrate bias was used in the deposition, or when the WC_1−x phase was detected by X-ray diffraction. The adhesion of the coatings is very low with spontaneous spallation of those deposited with negative substrate bias higher than 45 V. Varieties in cathode power (90 W or 120 W) applied to the W target showed no observable influence on the characteristics of the films.     

High temperature tribological behaviour of carbon based (B4C and DLC) coatings in sliding contact with aluminum

Carbon based coatings, particularly diamond-like carbon (DLC) films are known to resist aluminum adhesion and reduce friction at room temperature. This attractive tribological behaviour is useful for applications such as tool coatings used for aluminum forming and machining. However, for those operations that are performed at elevated temperatures (e.g. hot forming) or that generate frictional heat during contact (e.g. dry machining) the suitable coatings are required to maintain their tribological properties at high temperatures. Candidates for these demanding applications include boron carbide (B₄C) and DLC coatings. An understanding of the mechanisms of friction, wear and adhesion of carbon based coatings against aluminum alloys at high temperatures will help in designing coatings with improved high temperature tribological properties. With this goal in mind, this study focused on B₄C and a hydrogenated DLC coatings sliding against a 319 grade cast aluminum alloy by performing pin-on-disk experiments at temperatures up to 400 °C. Experimental results have shown that the 319 Al/B₄C tribosystem generated coefficient of friction (COF) values ranging between 0.42 and 0.65, in this temperature range. However, increased amounts of aluminum adhesion were detected in the B₄C wear tracks at elevated temperatures. Focused ion beam (FIB) milled cross sections of the wear tracks revealed that the coating failed due to shearing along the columnar grain boundaries of the coating. The 319 Al/DLC tribosystem maintained a low COF (0.15-0.06) from room temperature up to 200 °C. This was followed by an abrupt increase to 0.6 at 400 °C. The deterioration of friction behaviour at T > 200 °C was attributed to the exhaustion of hydrogen and hydroxyl passivants on the carbon transfer layer formed on the Al pin.     

Influence of the annealing temperature on a crystal phase of W/WC bilayers grown by pulsed arc discharge

The X-ray diffraction technique was used to study the influence of the temperature on a crystal phase of W/WC bilayer produced by the plasma-assisted pulsed arc discharge. In order to grow the films, a target of W with 99.9999% purity and stainless-steel 304 substrate were used. For the production of W layer, the reaction chamber was filled up with argon gas until reaching a 300 Pa and the discharge was performed at 270 V with 3 pulses. The WC layer was grown in a methane atmosphere at 300 Pa and 275 V discharge voltage with 4 pulses. The active and passive times of the pulsed discharge were 1 and 0.5 s, respectively. The influence of post-annealing temperature of their crystal phases was studied at the post-annealing temperatures up to 600 °C. As-grown layer comprised of mixed phases WC, W₂C and W. The post-annealed layer also comprised of the mixed phases of WC, W₂C and W at annealing temperatures below 600 °C. At the annealing temperature above 600 °C, XRD diffractograms showed only substrate and W peaks, and tungsten carbide peaks were not observed, but the presence of WO phases were detected for an annealing temperature of 600 °C. XPS analyses showed the presence of WC before the annealing process and the existence of C-C bond that is considered responsible for the high polycrystallinity of the material was also detected. The XPS showed the formation of WO₂ and WO₃ without the presence of WC for post-annealing at 600 °C.     

Strong amorphization of high-entropy AlBCrSiTi nitride film

Amorphous coatings, particular nitride systems, are of interest for numerous practical applications. Nevertheless, at present only a few amorphous nitride coating systems have been considered, the most notably being the (TM, Si)N system (transition metal (TM) = Ti, Zr, W, Mo). The present study provides an alternative approach for producing amorphous nitride films with high thermal stability up to 700 °C for 2 h. Films are deposited from an equimolar AlBCrSiTi target in various argon/nitrogen atmospheres at different substrate temperatures. It is found that above the nitrogen flow ratio (i.e. R_N = N₂/N₂ + Ar) of 28.6% a near equal ratio between target elements and nitrogen is approached, thus indicating the coatings have the chemical formula of (AlBCrSiTi)N. The glancing-angle X-ray diffractometer and transmission electron microscope investigations indicate that the coatings, regardless of nitrogen concentration or deposition temperature (up to 500 °C), are amorphous. Thermal treatment shows that the amorphous structure of this (AlBCrSiTi)N coating is maintained up to 700 °C when annealing for 2 h in vacuum. At annealing temperatures of 800 °C and above, the amorphous films transform into a simple NaCl-type face-centered cubic solid solution. Even after annealing at 1000 °C for 2 h, the grain size is only 2 nm. High entropy effect, large lattice distortion effect, and sluggish diffusion effect are proposed to account for the formation of amorphous nitrides.     

Structure and mechanical properties of low temperature magnetron sputtered nanocrystalline (nc-)Ti(N,C)/amorphous diamond like carbon (a-C:H) coatings

This paper reports on the structure and mechanical properties of ~ 2 μm thick nanocomposite (nc-) Ti(N,C)/amorphous diamond like carbon (a-C:H) coatings deposited on 100Cr6 steel substrates, using low temperature (~ 200 °C) DC reactive magnetron sputtering. The carbon content was varied with acetylene partial pressure in order to obtain single layer coatings with different a-C:H carbon phase fractions. The nanocrystalline Ti(N,C) phase is approximately stoichiometric for all coatings and the a-C:H phase fraction increases from 31 to 47 at.% as the coatings stoichiometry changed from TiC_1.34 N_0.51 to TiC_2.48 N_0.48, respectively. TiC_1.34 N_0.51 coatings showed the highest nanoindentation hardness (H) of ~ 14 GPa and a modulus (E_r) of ~ 144 GPa; H reduced to < 6 GPa and E_r to < 70 GPa for TiC_2.48 N_0.48 coatings. nc-Ti(N,C)/a-C:H coatings are promising candidates for applications where better matching of the modulus between a relatively low modulus substrate, hard loading support layer and low modulus-high H/E ratio top layer is required.     

Composition, structural and electrical properties of thin films prepared by laser ablation of neodymium-doped potassium gadolinium tungstate

Thin films were grown on (001) SiO₂, SiO₂/(100) Si or (100) MgO substrates by laser ablation of neodymium-doped potassium gadolinium tungstate (Nd:KGW) single crystal target. The films were deposited at temperatures between room temperature and 750 °C and pressures between 1 × 10^− 4 Pa and 50 Pa of oxygen ambient. The influence of the deposition conditions on the composition, structure, morphology and electrical properties of the films was investigated. Special attention was paid to the films deposited in vacuum (1 × 10^− 4 Pa) or at very low oxygen pressures. Under such conditions, the potassium (K), gadolinium (Gd) and oxygen (O) content decreased strongly as the temperature was increased. At room temperature, the films were K and O stoichiometric, in contrast with Gd, which showed a concentration twice higher. The films were polycrystalline, with the exception of those deposited at temperatures below 500 °C, which were amorphous. However, all were smooth and dense. The films grown in vacuum and at temperatures between 500 and 700 °C consist mainly of “â-tungsten” - tungsten oxide (W₃O) phase. The films grown on SiO₂/Si possessed the best surface quality with nano-size relief. The resistivity measurements as a function of the temperature showed that the films produced in vacuum and at temperatures below 500 °C were highly insulating, whereas at 600 °C they exhibited semiconducting behavior or a metallic one at 700 °C. This behavior can be attributed to the existence of various valence states for tungsten below W⁶⁺ in the films and to their crystal structure.     

Effect of post-deposition annealing on phase formation and properties of RF magnetron sputtered PLZT thin films

In this work, we report the preparation of lanthanum-modified lead zirconate titanate (PLZT) thin films by RF magnetron sputtering on platinized silicon (Pt/Ti/SiO₂/Si) substrate. Sputtering was done in pure argon at 100 W RF power without external substrate heating. X-ray diffraction studies were performed on the films to study the effect of post-deposition furnace annealing temperature and time on the perovskite phase formation of PLZT. Annealing at 650 °C for 2 h was found to be optimum for the preparation of PLZT films in pure perovskite phase. The effect of different annealing conditions on surface morphology of the films was examined using AFM. The dielectric, ferroelectric and electrical properties of these films were also investigated in detail as a function of different annealing conditions. The pure perovskite film exhibits better properties than the other films which have some fraction of unwanted pyrochlore phase. The remanent polarization for pure perovskite film was found to be ∼29 μC/cm² which is almost double compared to the films having mixed phases. The dc resistivity of the pure perovskite film was found to be 7.7 × 10¹⁰ Ω cm at the electric field of ∼80 kV/cm.     

Piezoelectric properties of Bi4Ti3O12 thin films annealed in different atmospheres

Bismuth titanate (Bi₄Ti₃O₁₂—BIT) films were evaluated for use as lead-free piezoelectric thin-films in micro-electromechanical systems. The films were grown by the polymeric precursor method on Pt/Ti/SiO₂/Si (1 0 0) (Pt) bottom electrodes at 700 °C for 2 h in static air and oxygen atmospheres. The domain structure was investigated by piezoresponse force microscopy (PFM). Annealing in static air leads to better ferroelectric properties, higher remanent polarization, lower drive voltages and higher piezoelectric coefficient. On the other hand, oxygen atmosphere favors the imprint phenomenon and reduces the piezoelectric coefficient dramatically. Impedance data, represented by means of Nyquist diagrams, show a dramatic increase in the resistivity for the films annealed in static air atmopshere.     

Microstructure and tribological behaviour of super-hard Ti-Si-C-N nanocomposite coatings deposited by plasma enhanced chemical vapour deposition

In this study, a series of new quaternary Ti-Si-C-N nanocomposite coatings have been deposited on HSS substrate at 550 °C using an industrial set-up of pulsed direct circuit plasma enhanced chemical vapour deposition (PECVD) equipment with a gas mixture of TiCl₄/SiCl₄/H₂/N₂/CH₄/Ar. The composition of the coatings can be controlled through the adjustment of CH₄ flow rate and the mixing ratio of the chlorides. Detailed structural and chemical characterisations using transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) suggest the formation of a Ti (C, N)/a-C/a-Si₃N₄ nanocomposite structure. Ti (C, N) films show a (200) texture, which change to random orientation of the crystallites when the silicon content reaches about 9 at.%. The tribological behaviour of these coatings was investigated at room and elevated temperature. The results show that the nanocomposite Ti-Si-C-N coatings with low Si and high C contents have a lower friction coefficient of 0.17-0.35 at room temperature. The Ti-Si-C-N nanocomposite coating containing 12 at.% Si and 30 at.% C shows excellent tribological properties with a low friction coefficient of 0.30 and a low wear rate of 4.5 × 10⁵ mm³ N^− 1m^− 1 at 550 °C.     

Sputter deposition from a Ti2AlC target: Process characterization and conditions for growth of Ti2AlC

Sputter deposition from a Ti₂AlC target was found to yield Ti-Al-C films with a composition that deviates from the target composition of 2:1:1. For increasing substrate temperature from ambient to 1000 °C, the Al content decreased from 22 at.% to 5 at.%, due to re-evaporation. The C content in as-deposited films was equal to or higher than the Ti content. Mass spectrometry of the plasma revealed that the Ti and Al species were essentially thermalized, while a large fraction of C with energies > 4 eV was detected. Co-sputtering with Ti yielded a film stoichiometry of 2:0.8:0.9 for Ti:Al:C, which enabled growth of Ti₂AlC. These results indicate that an additional Ti flux balances the excess C and therefore provides for more stoichiometric Ti₂AlC synthesis conditions.     

Effects of O addition on the thermal behaviour of hard W-N sputtered coatings

The structural thermal behaviour of three W-O-N sputtered coatings with similar metalloid to metal ratio (∼2.1) was investigated up to 900 °C after annealing in a vacuum tube furnace as well as in-situ HT-XRD under a controlled atmosphere of Ar-5%H₂. The as-deposited microstructure of the coatings consisting in a nanocomposite of low-order W-O and W-N phases evaluated differently as a function of the oxygen content. The W-O-N film containing more than 27 at.% O delaminated severely from the steel substrates for temperatures as low as 500 °C. In opposite, for the coatings with less O content, the low range order of the as-deposited structure was maintained up to 800 °C and with further annealing crystallized into a mixture of WO₂ and W₂N. The thermal behaviour of the oxynitride films overcame that observed for oxygen-free nitride ones. This is due to the greater N content retaining during annealing treatment, in opposite to the W-N films which give rise to the single metallic α-W phase. The structural and compositional evolution supported the hardness behaviour obtained by the thermal treatment in protective ambiance.     

CexAlyOz/TiN stack analysis for Metal-Insulator-Metal applications: Effect of annealing and the metal electrode deposition method

Ce_xAl_yO_z thin films were deposited on TiN metal electrode by metalorganic chemical vapour deposition method at 400 °C. The detailed physical characterization on Ce_xAl_yO_z/TiN stack upon annealing at different temperatures (600 °C and 850 °C) and for different deposition methods (Atomic vapour deposition (AVD) and Physical vapour deposition (PVD)) of electrode material were done for possible Metal-Insulator-Metal applications. X-ray diffraction results exhibited that the dielectric and TiN(AVD) are amorphous while TiN(PVD) is crystalline for the as deposited stacks. Annealing on Ce_xAl_yO_z/TiN(AVD) at 600 °C, initiates CeO₂ crystallization in the dielectric with composition of Ce:Al = 0.5 as obtained by X-ray photoelectron spectroscopy. In Ce_xAl_yO_z/TiN(PVD) stack, the dielectric remains in its amorphous state until 850 °C. However, TiO₂ crystallization is formed at 600 °C in Ce_xAl_yO_z/TiN(PVD). Time of flight secondary ion mass spectroscopy depth profiling data proves that the annealing at 600 °C caused the oxidation of both the metal electrodes and the inter-diffusion of Ti from the bottom metal electrode through the dielectric layer.