TiCN/TiNbCN multilayer coatings with enhanced mechanical properties

Enhancement of mechanical properties by using a TiCN/TiNbCN multilayered system with different bilayer periods (Λ) and bilayer numbers (n) via magnetron sputtering technique was studied in this work. The coatings were characterized in terms of structural, chemical, morphological and mechanical properties by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nanoindentation. Results of the X-ray analysis showed reflections associated to FCC (1 1 1) crystal structure for TiCN/TiNbCN films. AFM analysis revealed a reduction of grain size and roughness when the bilayer number is increased and the bilayer period is decreased. Finally, enhancement of mechanical properties was determined via nanoindentation measurements. The best behavior was obtained when the bilayer period (Λ) was 15 nm (n = 200), yielding the highest hardness (42 GPa) and elastic modulus (408 GPa). The values for the hardness and elastic modulus are 1.6 and 1.3 times greater than the coating with n = 1, respectively. The enhancement effects in multilayer coatings could be attributed to different mechanisms for layer formation with nanometric thickness due to the Hall-Petch effect; because this effect, originally used to explain the increase in hardness with decreasing grain size in bulk polycrystalline metals, has also been used to explain hardness enhancements in multilayers taking into account the thickness reduction at individual single layers that make the multilayered system. The Hall-Petch model based on dislocation motion within layers and across layer interfaces, has been successfully applied to multilayers to explain this hardness enhancement.     

Improvement of mechanical and tribological properties in steel surfaces by using titanium-aluminum/titanium-aluminum nitride multilayered system

Improvement of mechanical and tribological properties on AISI D3 steel surfaces coated with [Ti-Al/Ti-Al-N]_n multilayer systems deposited in various bilayer periods (Λ) via magnetron co-sputtering pulsed d.c. method, from a metallic binary target; has been studied in this work exhaustively. The multilayer coatings were characterized in terms of structural, chemical, morphological, mechanical and tribological properties by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), scanning electron microscopy, nanoindentation, pin-on-disc and scratch tests, respectively. The failure mode mechanisms were studied by optical microscopy. Results from X-ray diffraction analysis revealed that the crystal structure of TiAl/TiAlN multilayer coatings has a tetragonal and FCC NaCl-type lattice structures for Ti-Al and Ti-Al-N, respectively, i.e., it was found to be non-isostructural multilayers. An enhancement of both hardness and elastic modulus up to 29 GPa and 260 GPa, respectively, was observed as the bilayer periods (Λ) in the coatings were decreased. The sample with a bilayer period (Λ) of 25 nm and bilayer number n = 100 showed the lowest friction coefficient (∼0.28) and the highest critical load (45 N), corresponding to 2.7 and 1.5 times better than those values for the coating deposited with n = 1, respectively. These results indicate an enhancement of mechanical, tribological and adhesion properties, comparing to the [Ti-Al/Ti-Al-N]_n multilayer systems with 1 bilayer at 26%, 63% and 33%, respectively. This enhancement in hardness and toughness for multilayer coatings could be attributed to the different mechanisms for layer formation with nanometric thickness such as the novel Ti-Al/Ti-Al-N effect and the number of interfaces that act as obstacles for the crack deflection and dissipation of crack energy.     

Bilayer period effect on corrosion-erosion resistance for [TiN/AlTiN]n multilayered growth on AISI 1045 steel

The aim of this work is to study the electrochemical behavior, under a corrosion-erosion condition, of [TiN/AlTiN]_n multilayer coatings with bilayers periods of 1, 6, 12 and 24, deposited by a magnetron sputtering technique on Si (1 0 0) and AISI 1045 steel substrates.The TiN and AlTiN structure for multilayer coatings were evaluated via X-ray diffraction (XRD) analysis. Silica particles were used as an abrasive in the corrosion-erosion test within a 0.5 M H₂SO₄ solution at an impact angle of 30° over the surface. The electrochemical characterization was carried out using a polarization resistance technique (Tafel), in order to observe changes in the corrosion rate as a function of the bilayers number (n) or bilayer period (Λ). Corrosion rate values of 359 mpy in uncoated steel substrate and 1.016×10⁻⁶ mpy for substrate coated with [TiN/AlTiN]₂₄ under impact angle of 30° were found. This behavior was related with the mass loss curve for all coatings and the surface damage was analyzed using SEM images. These results indicate that TiN/AlTiN multilayer coatings deposited on AISI 1045 steel provide a practical solution for applications in erosive-corrosive environments.     

Influence of bilayer periods on structural and mechanical properties of ZrC/ZrB2 superlattice coatings

ZrC/ZrB₂ multilayered coatings with bilayer periods ranging from 4.4 to 35.5 nm were synthesized by r.f. magnetron sputtering. X-ray diffraction, scanning electron microscopy and nanoindention were employed to investigate the microstructure and mechanical properties of the nanoscale multilayers. The results indicated that all coatings had the clear multilayered structure with mixed ZrB₂(0 0 1), ZrB₂(0 0 2) and ZrC(1 1 1) preferred orientations. The maximum hardness (41.7 GPa) was observed in the multilayer with 27.5-nm thick period, which is about 25% higher than the rule-of-mixture value of the monolithic ZrC and ZrB₂ coatings. It also exhibited the best adhesion. Its critical load was over 70 mN. While through insert ZrB₂ into ZrC layer periodically, higher residual stress built in ZrC layer can be released.     

The effects of Si3N4 interlayer on the thermal stability and hardness of Ti/TiNx (x = 0.5-1) nanolayered coatings

The polycrystalline Ti/TiN_x multilayer films were deposited by magnetron sputtering, and the as-deposited multilayer coatings were annealed at 500-800 °C for 2-4 h in vacuum. We investigated the effects of annealing temperature and annealing time on the microstructural, interfacial, and mechanical properties of the polycrystalline Ti/TiN_x multilayer films. It was found that the hardness increased with annealing temperature. This hardness enhancement was probably caused by the preferred crystalline orientation TiN(1 1 1). The X-ray reflectivity measurements showed that the layer structure of the coatings could be maintained after annealing at 500 °C and the addition of the Si₃N₄ interlayer to Ti/TiN_x multilayer could improve the thermal stability to 800 °C.     

Comparative study of titanium carbide and nitride coatings grown by cathodic vacuum arc technique

Titanium nitride (TiN), titanium carbide (TiC) thin films and TiC/TiN bilayers have been deposited on AISI 304 stainless steel substrates by plasma assisted physical vapor deposition technique—reactive pulsed vacuum arc method. The coatings were characterized in terms of crystalline structure, microstructure and chemical nature by X-ray diffraction and X-ray photoelectron spectroscopy, respectively. Tribological behavior was investigated using ball on disc technique. The average coefficient of friction was measured, showing lower values for the TiN/TiC bilayer. Dynamic wear curves were performed for each coating, observing a better wear resistance for TiN/TiC bilayers, compared to TiN and TiC monolayers. On the other hand, the TiCN formation in the TiN/TiC bilayer was observed, being attributed to the interdiffusion between TiN and TiC at the interface. Moreover, the substrate temperature influence was analysing observing a good behavior at T_S = 115 °C.     

Heterostructures design for Hf-Nitride/V-Nitride system

The multilayered films were grown via reactive r.f. magnetron sputtering technique by systematically varying the bilayer period (Λ) and the bilayer number (n), while maintaining constant the total coating thickness (~2.4 μm) on silicon(100) substrates. The multilayers were characterized through high-angle X-ray diffraction (HA-XRD), low-angle X-ray diffraction (LA-XRD), HfN and VN layers were analyzed via X-ray Photoelectron Spectroscopy (XPS) and electron and transmission microscopy (TEM). The HA-XRD results showed preferential growth in the face-centered cubic (111) crystal structure for HfN/VN multilayer systems with the (111)[100]_HfN//(200)[100]_VN epitaxial relation. The maximum coherent assembly was observed with presence of satellite peaks.     

Structure and mechanical properties of titanium nitride/carbon nitride multilayers

The structure and mechanical properties of the multilayers consisting of 5-73 nm thick titanium nitride (TiN) and 4.6 nm thick carbon nitride (CN) have been investigated. It has been found that the CN layers are amorphous and the TiN layers thinner than 17 nm are amorphous. The TiN layers become crystallized as the thickness is increased to 30 nm or thicker. The hardness from the composite response of the multilayered films and their substrates determined using continuous stiff measurement is smaller than the film-only hardness (without substrate effects) calculated using Bhattacharya-Nix empirical equation. The hardness increases with raising the thickness of TiN layers. With the crystallization of the TiN layer, the multilayers become even harder than that calculated based on the rule of mixtures. However, no enhancement in hardness has been observed when the TiN layers are amorphous.     

Ti/TiN multilayer thin films deposited by pulse biased arc ion plating

In this work, the effect of modulation period (Λ) on Ti/TiN multilayer films deposited on high-speed-steel (HSS) substrates using pulse biased arc ion plating is reported. The crystallography structures and cross-sectional morphology of Ti/TiN multilayer films were characterized by X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM), respectively. Their mechanical properties were determined via nanoindentation measurements, while the film/substrate adhesion via the scratch test. It was found that the highest hardness value reached 43 GPa for the modulation period of 54 nm, while the film/substrate adhesion also reached the highest value of 83 N. Furthermore, the hardness enhancement mechanism in the multilayer films is discussed.     

Effect of annealing temperature on microstructure, hardness and adhesion properties of TiSixNy superhard coatings

A series of TiSi_xN_y superhard coatings with different Si contents were prepared on M42 steel substrates using two Ti and two Si targets by reactive magnetron sputtering at 500 °C. These samples were subsequently vacuum-annealed at 500, 600, 700, 800 and 900 °C, respectively. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), microindenter, Rockwell hardness tester and scratch tester were applied to investigate the microstructure, phase configuration, hardness and adhesion properties of as-deposited and annealed samples. The results indicated that there were two bonds, TiN and Si₃N₄, in all presently deposited TiSi_xN_y thin films, that structure was nanocomposite of nanocrystalline (nc-) TiN embedded into amorphous Si₃N₄ matrices. Annealing treatment below 900 °C played a little role in microstructure and hardness of the coatings although it greatly affected those of steel substrates. The film-substrate adhesion strength was slightly increased, followed by an abrupt decrease with increasing annealing temperature. Its value got to the maximum at 600 °C. Annealing had little effect on the friction coefficient with its value varying in the range of 0.39-0.40.     

Growth, microstructure, and mechanical properties related to modulation period for ZrAlN/ZrB2 superlattice coatings

ZrAlN/ZrB₂ multilayered superlattice coatings with modulation periods ranging from 20 nm to 60 nm were grown in magnetron sputtering chamber. X-ray diffraction (XRD), scanning electron microscopy (SEM) and nanoindention were employed to investigate the influence of modulation period on microstructure and mechanical properties of the multilayers. The sharp interfaces and nanoscale multilayered modulation were confirmed by SEM and XRD. The coating with modulation period of 40 nm and modulation ratio of 1:3 showed a marked polycrystalline structure with the strong mixture of ZrAlN (1 1 1), ZrB₂ (0 0 1) and ZrB₂ (1 0 1) textures. Meanwhile, it also possessed the highest hardness (36.4 GPa), elastic modulus (477 GPa), critical fracture load (76.48 mN), and lower residual stress, compared to those with other modulation periods and monolithic coatings.     

Enhanced ferroelectric properties of (Pb0.90La0.10)Ti0.975O3 multilayered thin films prepared by RF magnetron sputtering

The (Pb_0.90La_0.10)Ti_0.975O₃/PbTiO₃ (PLT/PT), PbTiO₃/(Pb_0.90La_0.10)Ti_0.975O₃/PbTiO₃ (PT/PLT/PT) multilayered thin films with a PbO_x buffer layer were in situ deposited by RF magnetron sputtering at the substrate temperature of 600 °C. With this method, highly (1 0 0)-oriented PLT/PT and PT/PLT/PT multilayered thin films were obtained. The PbO_x buffer layer leads to the (1 0 0) orientation of the films. The dielectric, ferroelectric and pyroelectric properties of the PLT multilayered thin films were investigated. It is found that highly (1 0 0)-oriented PT/PLT/PT multilayered thin films possess higher remnant polarization 2P_r (44.1 μC/cm²) and better pyroelectric coefficient at room temperature p (p = 2.425 × 10⁻⁸ C/cm² K) than these of PLT and PLT/PT thin films. These results indicate that the design of the PT/PLT/PT multilayered thin films with a PbO_x buffer layer should be an effective way to enhance the dielectric, ferroelectric and pyroelectric properties. The mechanism of the enhanced ferroelectric properties was also discussed.     

Nanolayered multilayer coatings of CrN/CrAlN prepared by reactive DC magnetron sputtering

Single-phase CrN and CrAlN coatings were deposited on silicon and mild steel substrates using a reactive DC magnetron sputtering system. The structural characterization of the coatings was done using X-ray diffraction (XRD). The XRD data showed that both the CrN and CrAlN coatings exhibited B1 NaCl structure with a prominent reflection along (2 0 0) plane. The bonding structure of the coatings was characterized by X-ray photoelectron spectroscopy and the surface morphology of the coatings was studied using atomic force microscopy. Subsequently, nanolayered CrN/CrAlN multilayer coatings with a total thickness of approximately 1 μm were deposited on silicon substrates at different modulation wavelengths (Λ). The XRD data showed that all the multilayer coatings were textured along {2 0 0}. The CrN/CrAlN multilayer coatings exhibited a maximum nanoindentation hardness of 3125 kg/mm² at a modulation wavelength of 72 Å, whereas single layer CrN and CrAlN deposited under similar conditions exhibited hardness values of 2375 and 2800 kg/mm², respectively. Structural changes as a result of heating of the multilayer coatings in air (400-800 °C) were characterized using XRD and micro-Raman spectroscopy. The XRD data showed that the multilayer coatings were stable up to a temperature of 650 °C and peaks pertaining to Cr₂O₃ started appearing at 700 °C. These results were confirmed by micro-Raman spectroscopy. Nanoindentation measurements performed on the heat-treated coatings revealed that the multilayer coatings retained hardness as high as 2250 kg/mm² after annealing up to a temperature of 600 °C.     

The ferroelectric and ferromagnetic characterization of CoFe2O4/Pb(Mg1/3Nb2/3)O3-PbTiO3 multilayered thin films

The multiferroic (PMN-PT/CFO)_n (n = 1,2) multilayered thin films have been prepared on SiO₂/Si(1 0 0) substrate with LNO as buffer layer via a rf magnetron sputtering method. The structure and surface morphology of multilayered thin films were determined by X-ray diffraction (XRD) and atom force microscopy (AFM), respectively. The smooth, dense and crack-free surface shows the excellent crystal quality with root-mean-square (RMS) roughness only 2.9 nm, and average grain size of CFO thin films on the surface is about 44 nm. The influence of the thin films thickness size, periodicity n and crystallite orientation on their properties including ferroelectric, ferromagnetic properties in the (PMN-PT/CFO)_n multilayered thin films were investigated. For multilayered thin films with n = 1 and n = 2, the remanent polarization Pr are 17.9 μC/cm² and 9.9 μC/cm²; the coercivity H_c are 1044 Oe and 660 Oe, respectively. In addition, the relative mechanism are also discussed.     

Microstructure and properties of Ni-Co/nano-Al2O3 composite coatings by pulse reversal current electrodeposition

Ni-Co/nano-Al₂O₃ (Ni-Co/Al₂O₃) composite coatings were prepared under pulse reversal current (PRC) and direct current (dc) methods respectively. The microstructure of coatings was characterized by means of XRD, SEM and TEM. Both the Ni-Co alloy and composite coatings exhibit single phase of Ni matrix with face-centered cubic (fcc) crystal structure, and the crystal orientation of the Ni-Co/Al₂O₃ composite coating was transformed from crystal face (2 0 0) to (1 1 1) compared with alloy coatings. The hardness, anti-wear property and macro-residual stress were also investigated. The results showed that the microstructure and performance of the coatings were greatly affected by Al₂O₃ content and the electrodeposition methods. With the increasing of Al₂O₃ content, the hardness and wear resistance of the composite coatings enhanced. The PRC composite coatings exhibited compact surface, high hardness, better wear resistance and lower macro-residual stress compared with that of the dc composite coatings.     

Microstructure, mechanical properties, and oxidation resistance of nanocomposite Ti-Si-N coatings

Ti-Si-N coatings with different silicon contents (0-12 at.%) were deposited onto Si(1 0 0) wafer, AISI M42 high speed steel, and stainless steel plate, respectively. These coatings were characterized and analyzed by using a variety of analytical techniques, such as XRD, AES, SEM, XPS, nanoindentation measurements, Rockwell C-type indentation tester, and scratch tester. The results revealed that the hardness was strongly correlated to the amount of silicon addition into a growing TiN film. The maximum hardness of 47.1 GPa was achieved as the Si content was 8.6 at.%. In the mechanical and oxidation resistance measurements, the Ti-Si-N coatings showed three distinct behaviors. (i) The coatings with Si contents of no more than 8.6 at.% performed good adhesion strength quality onto the HSS substrates. (ii) The fracture toughness of the coatings decreased with the increase in Si content. (iii) The Ti-Si-N coating with 8.6 at.% Si showed the excellent oxidation resistance behavior. The cutting performance under using coolant conditions was also evaluated by a conventional drilling machine. The drills with Ti-Si-N coatings performed much better than the drills with TiN coating and the uncoated drills.     

Effect of plasma treatment on interface property of BCN/GaN structure

Interface properties of BCN/GaN metal-insulator-semiconductor (MIS) structures are investigated by X-ray photoelectron spectroscopy (XPS) and capacitance versus voltage (C-V) characteristics measurements. The BCN/GaN samples are fabricated by in situ process consisting of plasma treatment and deposition of BCN film in the plasma-assisted chemical vapor deposition (PACVD) apparatus. XPS measurement shows that the oxide formation at the BCN/GaN interface is suppressed by nitrogen (N₂) and hydrogen (H₂) plasma treatment. The interface state density is estimated from C-V characteristics measured at 1 MHz using Terman method. The minimum interface state density appears from 0.2 to 0.7 eV below the conduction band edge of GaN. The minimum value of the interface state density is estimated to be 3.0 × 10¹⁰ eV⁻¹ cm⁻² for the BCN/GaN structure with mixed N₂ and H₂ plasma treatment for 25 min. Even after annealing at 430 °C for 10 min, the interface state density as low as 6.0 × 10¹⁰ eV⁻¹ cm⁻² is maintained.     

Surface characteristics of TiN/ZrN coated nanotubular structure on the Ti-35Ta-xHf alloy for bio-implant applications

In this study, we investigated the surface characteristics of the TiN/ZrN-coated nanotubular structure on Ti-35Ta-xHf ternary alloys for bio-implant applications. These ternary alloys contained from 3 wt.% to 15 wt.% Hf contents and were manufactured in an arc-melting furnace. The Ti-35Ta-xHf alloys were heat treated in Ar atmosphere at 1000 °C for 24 h, followed by water quenching. Formation of the nanotubular structure was achieved by an electrochemical method in 1 M H₃PO₄ electrolytes containing 0.8 wt.% NaF. The TiN coating and ZrN coating were subsequently prepared by DC-sputtering on the nanotubular surface. Microstructures and nanotubular morphology of the alloys were examined by FE-SEM, EDX and XRD. The microstructure showed a duplex (α′′ + β) phase structure. Traces of martensite disappeared with increasing Hf content, and the Ti-35Nb-15Hf alloy had an entirely equiaxed structure of β phase. This research has shown that highly ordered, high aspect ratio, and nanotubular morphology surface oxide layers can be formed on the ternary titanium alloys by anodization. The TiN and ZrN coatings formed on the nanotubular surfaces were uniform and stable. The top of the nanotube layers was uniformly covered with the ZrN film compared to the TiN film when the Ti-35Ta-xHf alloys had high Hf content.     

Coating formation by plasma electrolytic oxidation on ZC71/SiC/12p-T6 magnesium metal matrix composite

Plasma electrolytic oxidation (PEO) of a ZC71/SiC/12p-T6 magnesium metal matrix composite (MMC) is investigated in relation to coating growth and corrosion behaviour. PEO treatment was undertaken at 350 mA cm⁻² (rms) and 50 Hz with a square waveform in stirred 0.05 M Na₂SiO₃.5H₂O/0.1 M KOH electrolyte. The findings revealed thick, dense oxide coatings, with an average hardness of 3.4 GPa, formed at an average rate of ∼1 μm min⁻¹ for treatment times up to 100 min and ∼0.2 μm min⁻¹ for later times. The coatings are composed mainly of MgO and Mg₂SiO₄, with an increased silicon content in the outer regions, constituting <10% of the coating thickness. SiC particles are incorporated into the coating, with formation of a silicon-rich layer at the particle/coating interface due to exposure to high temperatures during coating formation. The distribution of the particles in the coating indicated growth of new oxide at the metal/coating interface. The corrosion rate of the MMC in 3.5% NaCl is reduced by approximately two orders of magnitude by the PEO treatment.     

Λ-Doubling investigation of the 5Πg Rydberg state of Na2 using optical-optical double resonance spectroscopy

The splitting of Λ-doubling in the 5¹Π_g Rydberg state of Na₂, which dissociates to Na(3s) + Na(4d), has been measured using the high-resolution cw optical-optical double resonance technique. The observed data are in the range of 0 ? v ? 22 and 11 ? J ? 83 with Λ-doubling revealed. A set of Dunham coefficients with Λ-doubling constants has been obtained from the experimental results. The splitting of Λ-doubling increases quadratically with the rotational quantum number J and weakly depends on the vibrational quantum number v. These splitting constants are much larger than those in the Na₂B¹Π_u state, which dissociates to Na(3s) + Na(3p). This indicates that the splitting of Λ-doubling in the 5¹Π_g state is affected by both the perturbations by adjacent Σ states and the L-uncoupling.