ICMCTF2013 Session BP: Syposium B Poster Session

We investigated the mechanical and physicochemical properties of CrN/Si₃N₄ multilayered coatings in the period interval 2 to 10 nm, produced by depositing the thin film multilayer structure at substantially higher substrate temperatures than in previously reported works. This resulted in an appreciable increase in hardness at a multilayer period around 4 nm, as well a corresponding increase in the resistance to plastic deformation of the coating for multilayer periods around 4 to 6 nm. The various physicochemical characterization techniques used here revealed that the individual CrN and Si₃N₄ layers were stoichiometric and the interfaces were abrupt, while the Si₃N₄ layers were amorphous and the CrN ones crystalline. Furthermore, Si is mainly bonded to N as Si₃N₄ and maybe some other non-stoichiometric Si-N compound, whereas Cr was bonded as CrN and chromium oxides.

Keywords: Multilayers; Hardness; Si₃N₄/CrN

The physical, electrical and reliability characteristics of the HfO₂ gate stack fabricated by a single-step and a multiple-step deposition-annealing method are compared in this study. After the same high temperature (750^oC) annealing, the single-step HfO₂ has transformed into a polycrystalline phase, while the multi-step HfO₂ is found to remain in a nanocrystalline phase, indicating that a multi-step deposition-annealing method could significantly improve the thermal stability of the high-k HfO₂ film with respect to the grain formation process. Additionally, the density and composition of the high-k HfO₂ film are enhanced by multi-step deposition-annealing process. These changes lead to an improvement in the electrical characteristics, breakdown voltage, and reliability of the multi-step HfO₂ film. The reliability characteristics of multi-step deposition-annealed HfO₂ dielectric under unipolar and bipolar AC stresses were also evaluated. Dielectric breakdown failure time of bipolar AC stress becomes longest in comparison to the other two stresses. Moreover, as the number of deposition-annealing steps increases, a larger lifetime enhancement is detected due to the effective charge de-trapping for multi-step deposition-annealed HfO₂ dielectrics under bipolar stress.

The paper presents the comparison of the structures of the zirconium modified aluminide coatings deposited on pure nickel by the CVD and PVD processes.

In the CVD process, zirconium was deposited from the ZrCl₃ gas phase at the 1000 ºC. In the PVD process, the zirconium layer 7 μm thick and the aluminum layer 0.5 μm thick or zirconium layer 7 μm thick and the aluminum layer 0.7 μm thick were deposited by the Electron Beam Evaporation method. Deposition velocity was about 1 μm/min. The layers obtained by the Electron Beam Evaporation method were subjected to diffusion heating at 1050 ºC for 2 h in the argon atmosphere. The obtained coatings were examined by the use of an optical microscope (microstructure and coating thickness ) a scanning electron microscope ( chemical composition on the cross-section of the modified aluminide coating) and XRD phase analysis. Microstructures and phase compositions coatings obtained by different methods are differ significantly. NiAl(Zr), Ni₃Al and Ni(Al) phases were found in the CVD aluminide coatings, whereas Ni₅Zr and γNi(AlZr) were observed in coatings obtained by the PVD method. The results indicate, that the microstructure of the coating is strongly influenced by the method of manufacturing.

Alloying Ti-Al-N with Ta has proven to enhance the hardness, thermal stability and oxidation resistance of sputter deposited coatings. To meet a balance between all these requirements for protecting tools during drilling and cutting applications, an optimized chemical composition of Ti, Ta and Al within the cubic stability range is necessary. However, only limited information is available on arc-evaporated Ti-Al-Ta-N coatings. Therefore, coating developments with an industrial scaled INNOVA Oerlikon Balzers plant, using powder metallurgical (Ti_0.50Al_0.50)_0.95Ta_0.05, (Ti_0.50Al_0.50)_0.90Ta_0.10, (Ti_0.34Al_0.66)_0.95Ta_0.05 and (Ti_0.34Al_0.66)_0.90Ta_0.10 targets, were carried out and investigated with respect on their phase stability, mechanical properties as well as thermal stability and oxidation resistance. Vacuum annealing treatments exhibit retarded film decomposition by the addition of Ta. Consequently, the formation of the stable wurzite AlN phase is shifted to higher annealing temperatures of ~1200°C, accompanied by the formation of hexagonal Ta₂N. Furthermore, alloying Ta to Ti-Al-N promotes the formation of a dense oxide scale. Therefore, the Ti-Al-Ta-N coating is still intact under a protective oxide, even when treated at 950°C for 20h in ambient air.

In this work two different superhard coatings that improve the corrosion resistance were prepared, Nb-N-Si and Ta-N-Si.

The coatings were deposited using a reactive dual magnetron sputtering system, using two targets, one metallic target (Nb or Ta) and a silicon target, in a reactive mixture of gases (argon and nitrogen). Coatings with different concentrations of silicon were grown, which was controlled by varying the RF-power applied on the silicon target.

The microstructural properties, measured using X-ray diffraction, showed the growth of crystalline coatings presenting the FCC phase of the metallic nitrides (NbN or TaN). The composition of the films was measured using x-ray photoelectron spectroscopy (XPS). The hardness was obtained using the nanoindentation technique, finding the maximum values of hardness around to 5% at. of Si in both systems (Ta-N-Si and Nb-N-Si), with values higher of 35 GPa for the Nb-N-Si, and higher of 40 GPa for the Ta-N-Si.

The hardest films of Nb-N-Si and Ta-N-Si were grown on stainless steel substrates and evaluated using two different electrochemical techniques: DC polarization and electrochemical impedance spectroscopy. The films were compared with the substrate and with the NbN and TaN without silicon inclusion. The results showed a good improvement of the corrosion resistance in comparison to both the bare substrate and the metal nitride coating without silicon.

Scratch test was used to measure the adhesion of the coatings to the substrate, and the results showed that the Si inclusion in the TaN system improved the adherence of the coating compared with the TaN. However in the system of the Nb-N-Si there were not significant changes in the substrate-coating adhesion relative to the NbN coatings.

The most important conclusion of this research was that it was possible to design coatings presenting both properties; corrosion resistance and high hardness.

Acknowledgements: We wish to acknowledge the financial support from DGAPA-UNAM IN103910. G. Ramírez acknowledges CONACYT for his PhD scholarship.

The paper deals with characteristics of ternary (M₁M₂N) and quaternary (M₁M₂M₃N) metal nitrides (M = Ti, Zr, Hf, V, Nb or Ta) of various compositions obtained by ab-initio calculations. We focus on comparison of formation energies (E₀), bulk moduli (B), shear moduli (G) and an improvement of B and G over weighted average of B and G of binary metal nitrides (ΔB and ΔG) with electronegativities and atomic radii of the constituent elements.

For elastic moduli of M₁M₂N we find that ΔB (up to 19 GPa), ΔG (up to 20 GPa) and G itself increase with increasing difference between atomic radii of M₁ and M₂. In parallel, higher E₀ leads to higher ΔB (but lower B), and higher |E₀| leads to higher ΔG.

For formation energies of M₁M₂N we find that (i) close atomic radii of M₁ and M₂ are sufficient for close to zero or highly negative E₀, while (ii) close electronegativities of M₁ and M₂ are necessary for highly negative E₀. The solubility of M₁N and M₂N surprisingly increases (formation energy of M₁M₂N decreases) with increasing difference between electronic structures of M₁N and M₂N. The lowest E₀ values were observed for Ta-containing M₁M₂N compositions.

For formation energies of quaternary M₁M₂TaN we show that in agreement with the above statement, E₀ is in all cases lower compared to M₁M₂N (at higher B). The drop in E₀ (improved solubility) resulting from Ta incorporation is more significant for lower atomic radius and higher electronegativity of the other metals M₁ and M₂.

Overall [1], we present trends which allow one to understand and predict which materials form (stable) solid solutions, and which materials exhibit enhanced elastic moduli. There is a special role of tantalum in stabilizing the solid solutions. The phenomena shown can be tested experimentally, and examined for a wider range of materials.

[1] V. Petrman and J. Houska, J.Phys: Condens. Matter, submitted (2012)

Nb–Ru multilayer coatings with various chemical compositions were deposited on silicon wafers by using a direct current magnetron co-sputtering system. By varying the substrate-holder rotation speeds, the Nb–Ru coatings exhibited distinct nanolaminated structures with various periods. The annealing treatments were conducted at 400^oC, 500^oC, and 600^oC under atmospheres of 50-ppm O₂–N₂ and 1% O₂–Ar, respectively. The Nb oxidized preferentially when annealed in oxygen-containing atmospheres. The oxidized Nb–Ru coatings formed a nanolaminated oxide/metal structure, attributed to the internal oxidation behavior. The maintenance of nanolaminated structure for various Nb–Ru coatings after annealing was studied. The variations in crystalline structure, nanohardness, surface roughness and chemical composition of Nb–Ru coatings caused by annealing were widely investigated.

In order to improve the mechanical properties, wear resistance and high temperature oxidation resistance of CrN coatings, alloying with other group IIIB-VIB transition metal (TM) elements (e.g., Y, Ti, Zr, Hf, V, Nb, Ta, Mo, W) becomes an important concept in the industrial area, and hence attracts also attention of the scientific community. In this paper with present an extensive first principles study of the phase stability, structural and elastic properties of Cr-containing cubic TM nitrides, where Cr substitutes for TM (i.e. Cr_1-xTM_xN). The calculated equilibrium lattice parameters exhibit a deviation from Vegard’s linear interpolation to larger values. An addition of a small amount of TM elements into CrN results in softening of the material as measured by the bulk modulus, while significant increase in bulk modulus is predicted for Ta- and Nb-rich Cr_1-xTM_xN alloys (x>0.6). The phase stability is studied as a function of the TM valence electron concentration and thus linked with the electronic structure. Finally, the single crystal elastic constants of Cr_0.5TM_0.5N are calculated using the stress-strain method. Employing some representative sample textures allows us to discuss the influence of the TM on the polycrystalline elastic behavior of CrN. All these compositional trends are compared with the available experimental data.

Al_xCr_1-xN coatings are highly valued for various industrial applications based on their outstanding mechanical properties and oxidation resistance. Even though deposition parameters like partial pressure, gas mixture or temperature are well investigated and optimized; only little information is available on the influence of the target material itself. Therefore, Al_xCr_1-xN coatings were deposited by reactive and non-reactive unbalanced magnetron sputtering using three different powder-metallurgically prepared targets: a metallic Al/Cr target, an intermetallic AlCr_x target and a ceramic AlN/CrN target. XRD analyses indicate for all targets tested a single cubic microstructure. The coatings deposited from the metallic and intermetallic target demonstrate a columnar structure with a pronounced (111) orientation whereas the coating deposited from the ceramic target is fine crystalline with (200) orientation. Furthermore, the hardness is highest for those coatings prepared from the ceramic target material.

Mechanical properties, thermal stability and oxidation resistance of Ti_1-xAl_xN coatings are well investigated and recent studies indicated that these properties can considerably be improved by alloying elements such as Cr, Ta or Y to form quaternary nitrides. However within this study we want to focus on an architectural approach by depositing multilayer arrangements of TiAlN and TaAlN. Further on, combined processing of reactive arc-evaporated Ti_1-xAl_x targets with either arced (arc) or sputtered (rsd) Ta_1-yAl_y targets are carried out opening the possibility to deposit coatings with variable chemical and structural modulations.

Our investigations show that the TiAlN_arc/TaAlN_arc multilayers exhibit enhanced thermal phase stability with peak hardness values of ~ 35 GPa up to T_a=1200 °C, whereas the TiAlN_arc/TaAlN_rsd multilayers exhibit hardness values of ~35 GPa up to T_a=800 °C which decrease to ~32 GPa when T_a=1100 °C. However, oxidation investigations clearly demonstrate the advantage of this hybrid arc/rsd process as the TiAlN_arc/TaAlN_rsd nitride coatings still remain intact after oxidising in air at 850 °C for 20 h, whereas the TiAlN_arc/TaAlN_arc multilayer coatings are completely oxidised.

Advanced tribological properties, high temperature oxidation resistance, excellent corrosion performance of Ti alloy coatings (such as TiN, TiAlN and TiAlN/CrN) make them an important candidate to be utilized in many applications such as tool coatings. In actual working environments one of the main degradation causes of thin films is corrosion; therefore its evaluation processes have high importance. In the present study, TiAlN/TiCrN multilayer coatings were deposited by closed field unbalanced magnetron sputtering from two Cr, one Al and one Ti targets. The structural properties of coatings have been analyzed by electron microscopy (SEM), X-Ray diffraction (XRD) and energy dispersive spectrometry (EDS). Additionally, corrosion properties of these coating were investigated by using polarization test unit.

Brominated amorphous hydrogenated carbon films were produced by the plasma polymerization of bromoform-acetylene mixtures. There is little extant literature on this type of film. Varying the proportion of bromoform in the mixture allowed the production of non-brominated to highly brominated films (up to about 43 at% Br); thus the main parameter of interest was the degree of bromination, R_B. The films were characterized by Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photo-electron Spectroscopy (XPS). Ultraviolet-visible Near-Infrared Spectroscopy was employed to allow calculation of the optical properties, such as the refractive index, n, absorption coefficient, α(E), where E is the photon energy, and the optical gap, E_g, as a function of R_B. Semi-empirical modeling of E_g as a function of R_B was applied. In addition, nano-indentation studies revealed the hardness, modulus and stiffness of the films.

We employ Density Functional Theory modelling to study the effect of early transition metal (TM) elements (Y, Zr, Nb, Hf, and Ta) on the structural and mechanical properties of Ti–Al–TM–N and Cr–Al–TM–N systems.

While Y decreases significantly the maximum solubility of AlN in the cubic phase of the alloy, the other elements have only a negligible effect when their amount is less than ~10at.% on the metallic sublattice. The lattice parameter bows out to larger values as compared with Vegard's linear interpolation, owing to a gradually changing character of the bonds in the alloy with composition. The chemical strengthening is most pronounced for Ta and Nb, although also causing smallest elastic distortions of the lattice due to their atomic radii being comparable with Ti and Al. This is further supported by the analysis of the electronic density of states.

Mixing enthalpy, used as a measure of the driving force for decomposition into the stable constituents, is enhanced by adding Y, Zr and Nb, suggesting that the onset of spinodal decomposition will appear in these cases for lower thermal loads than for Hf and Ta alloyed Ti_1-xAl_xN.

Recently, we developed a novel method for the preparation of several micrometer thick super-hard tetrahedral amorphous carbon (ta-C) films with low internal stress. The method is a combination of excimer laser ablation for film deposition and excimer laser irradiation of as-deposited sub-layers for the reduction of the high stresses.

We will show that the variation of the laser beam spot size on the target surface influences the creation of particulates in the ta-C layers. With this the mechanical properties are affected. For the investigations ta-C layers have been deposited on hard metal substrates using only the nearly perpendicularly from the target surface ablated species. With the SEM, the particulates will be characterized. Nanoindentation was used for the measurement of hardness and the scratch test shows the critical loads.

Furthermore the influence of the repetition rates of the laser beam during the ablation process was analyzed. It was found that mechanical properties are not affected by the change of the repetition rates.

We will show that this variation of the laser beam spot size with the particulates must be taken into account if the mechanical properties of the ta-C layers should be optimized and that the deposition rate can be increased by using higher laser beam repetition rates.

In this study, TiN/TaN and TiN/TaN doped CrY multilayer coatings were deposited on M2 substrates using Closed Field Unbalanced Magnetron Sputtering (CFUBMS). The structural properties of coatings were analyzed by using Xray Photoelectron Spectroscopy (XRD), (energy-dispersive spectroscopy) EDS, Scanning Electron Microscopy (SEM). The hardness values of coatings were determined with a microhardness tester. Friction and wear properties of the coatings were determined by using pin-on-disc tribometer at humid air and high temperature.

Key Words: TiN/TaN, CrY, multilayer coatings, CFUBMS

In static oxidation, the formed titanium oxide (TiO2) was found to have mainly anatase structure at temperatures between 500ºC to 600ºC and transform to rutile structure at temperature higher than 600ºC. Through this study, oxidation rate and activation energy of oxidation for each sample were evaluated. It is found the samples exhibited higher activation energy could have higher oxidation resistance. These results are consistent with those obtained from wear testing.

Metals foils have been increasingly used as alternative substrates for the flexible dye-sensitized solar cells (DSSCs) to overcome the limitations arising from the low sintering-temperature tolerance of the plastic substrates. However, the potential problem of metal corrosion in the iodide-based electrolytes threatens to degrade the performance and long-term stability of the metal-based DSSCs. To resolve this dilemma, we have employed unbalanced magnetron sputtering systems to prepare nanocrystalline TiN barriers on the metal substrates as a photo-electrode. The energy conversion efficiency of TiN deposited DSSC reaches about 4.5% under illumination with a light intensity of 100mW^-2. The improved durability of DSSC has also been observed as compared to uncoated metal based DSSC. The mechanism of enhanced efficiency and durability of TiN coated DSSC will be discussed in this talk.

Nano-structured carbon films with cross-linked graphitic sheets exhibited good mechanical and electrical properties. When applying the films in the ultra precision system, very smooth surface is needed. We studied that the nanostructure of carbon films was tailored by ion irradiation energy in electron cyclotron resonance (ECR) sputtering, and the surface morphology was smoothed simultaneously. The nanostructure and bonding configuration were characterized by transmission electron microscopy (TEM) observation, Raman and X-ray photoelectron spectroscopy (XPS) spectra analysis. Upon increasing of ion irradiation energy, the graphitic sheets in nanocrystalline graphite were cross-linked with sp³ bonds. XPS results and the peak density ratio of I_D/I_G from Raman spectra also showed the increase of sp³ bonds content. The surface morphology of the nano-structured carbon films were tested by atomic force microscopy (AFM). Results indicated thatthe mean surface roughness (Ra) was decreased from 0.2 nm to 0.03 nm when the nanostructure changed from graphite clusters to cross-linked graphitic sheets. Super smooth carbon films correlated with the cross-linked graphitic sheets nanostructure was obtained by ECR ion irradiation.

CrN/AlN multilayer coatings exhibit improved mechanical properties and thermal stability, especially when a superlattice structure is formed. To obtain this superlattice structure both layer materials (CrN and AlN) have to exhibit the same crystal structure and a similar lattice parameter. However, a systematic study on the influence of the individual layer thicknesses of CrN and AlN on structural and mechanical properties of CrN/AlN superlattice coatings is still missing. Therefore, CrN/AlN multilayer coatings were prepared by DC reactive magnetron sputtering with AlN layer thicknesses of 1, 2, and 3.3 nm and varying the CrN layer thicknesses from 0.9 to 10 nm. The thereby obtained bilayer period (Λ) and structure of the CrN/AlN coatings was investigated by low-angle and high-angle X-ray diffraction (LAXRD and HAXRD) as well as high-resolution transmission electron microscopy (HRTEM). The hardness as a function of Λ was determined with an ultra-micro-indentation system and the residual stresses were obtained by the substrate-curvature method at room temperature.

The results suggest that the minimum CrN layer thickness, necessary to stabilize the AlN layers in their metastable cubic structure, is in the range of the AlN layer thickness themselves. Hence, for the CrN/AlN coatings composed of 1, 2, and 3.3 nm thin AlN layers the CrN layers need to be at least 1, 2, and ~3 nm, respectively. For thinner CrN layers an X-ray amorphous structure or a multiphase arrangement of cubic, wurtzite-like, and amorphous phases is obtained. Exemplarily, the CrN/AlN superlattice coating composed of 1 nm thin AlN and 1.9 nm thin CrN layers (Λ = 2.9 nm) was investigated by cross-sectional HRTEM. These studies confirmed the superlattice structure–suggested by LAXRD and HAXRD–by the almost perfect hetero-epitaxial relationship between c-CrN and c-AlN. This CrN/AlN superlattice coating, as well as the one composed of 2 nm thin AlN and 3.5 nm thin CrN (Λ = 5.5 nm) exhibit a hardness maximum of ~31 GPa. If the AlN layer thickness is ~3.3 nm the hardness peak is obtained only with ~28.5 GPa for a bilayer period of Λ = 6.3 nm. The resulting hardness-peak as a function of the bilayer period becomes broader with increasing AlN layer thickness. A corresponding dependence on the bilayer period is also obtained for the compressive stresses.

In this study, the Mo thin films were deposited on soda lime glass substrates through varies sputtering current by DC magnetron sputtering system. The structure of Mo films showed (110) preferred orientation. The electrical properties of Mo films indicated well conductive in this study. The mechanical properties of Mo thin films which were measured by nano-indentation, and the adhesion properties of interface between glass substrate and Mo film were investigated by nano-scratch. We were found that interface adhesion energy between Mo film and glass substrate was enhanced from 0.06 to 9.48 J/m², as sputtering current was increased. In this study, we were offered quantitative method to analysis adhesion properties, also including verify the feasibility in tribological application.

Si-doping (AlCrTaTiMo)N coatings were deposited onto Si substrate by the radio-frequency (RF) magnetron sputtering of a AlCrTaTiMo alloy target under direct current bias in a N₂/Ar atmosphere. The crystal, microstructural, mechanical, and electrical properties at different N₂-to-total (N₂+Ar) flow-rate ratios (R_N) values were investigated. As the silicon content reached 7.43 at%, the nitride remained as a simple NaCl-type face-centered cubic (FCC) structure. The lattice decline occur, implying that the incorporated silicon atoms can dissolve into the (AlCrTaTiMo)N lattice by substitution. The silicon incorporation significantly improved the mechanical properties and oxidation resistance of (AlCrTaTiMo)N coatings, however, deteriorated the electrical properties.

TiO₂ coatings are still widely studied because of numerous potential industrial applications especially in the environmental fields such as water purification technology, due to its chemical stability, low toxicity, corrosion resistance and low cost [1].

In this study, TiO₂ thin films are deposited by reactive magnetron sputtering at high pressure on heated glass slides substrates (from 250 to 550 °C). All of the substrates are covered by 250 nm SiN_x barrier layer to avoid the alkali elements diffusion of glass and degradation of TiO₂ photocatalytic activity [2-3]. X-ray diffraction, scanning electron microscopy, water angle contact measurement and Orange G decomposition upon UV irradiation are used as characterization technics.

Synthesized films were crystallized in anatase phase and their morphology exhibits a porous structure. The study of the photo-induced properties shows an activity maximum at 450 °C.

Finally, microstructural and photocatalytic properties of the TiO₂ coatings in-situ crystallized are compared with those of the films prepared under the same conditions but crystallized ex-situ.

The aim of the present work is to study the thermal stability, under vacuum and air annealing, of quaternary transition metal nitride films, namely TiZrAlN, with emphasis on the role of Al content on the structure and phase formation.

(Ti,Zr)_1-xAl_xN films with thickness of 300 nm have been deposited onto Si (001) wafers by reactive unbalanced magnetron co-sputtering from individual metallic targets under mixed Ar+N₂ plasma discharges. Ti and Zr targets were operated in dc mode, at fixed power of 300 and 220 W, respectively, while an RF power was applied to the Al target. The working pressure during deposition was fixed at 0.19 Pa. Varying the RF power of the Al target from 20 to 200 W resulted in metallic atomic fraction of aluminum, x, in the films to increase from 0.026 to 0.364, while the Ti:Zr concentration ratio was kept constant to ~1.0. RBS analysis revealed that N content decreased from ~50 at.% for low Al content (x<0.10) to ~30 at.% for x>0.25.

XRD, AFM, SEM and TEM analyses revealed a structural and morphological evolution upon Al incorporation in the TiZrN lattice. Three growth regimes were identified: i) nanocrystalline TiZrAlN solid solutions with cubic structure for x< 0.11, ii) dual-phase nanocomposites consisting of cubic TiZr(Al)N nanograins surrounded by amorphous TiAlN matrix for 0.11 < x < 0.25, and iii) XRD amorphous films for x> 0.25.

Annealing in vacuum (~10^-4 Pa) at the temperature of 600°С doesn't cause any structural changes of TiZrAlN films. After annealing in vacuum at 950°С, the structure of the films depends essentially on the aluminum content. Cubic TiZrAlN films with x=0 and 0.048 remained stable, while phase decomposition into c-TiN and c-ZrN was revealed for x>0.10.

Annealing under air atmosphere was carried out for temperature intervals ranging from 400 to 950°С using in situ temperature XRD. For low Al content (x<0.13), oxidation started at 500°C. Interestingly, an intermediate oxidized amorphous phase was found in the 600-700°C temperature range, followed by crystallization of the orthorhombic (ZrTi)O₄ oxide phase at 780°C. For x>0.25, the reduction of oxide formation can be explained by the passivating role of the Al₂O₃ outer layer. Thus, amorphous TiZrAlN films with high Al content are desirable for a better oxidation resistance.

Tetrahedral amorphous-carbon (ta-C) is hydrogen-free and high-density diamond-like carbon (DLC) film. In particular, chemical inertness, since it is able to prevent the adhesion of glass at high temperature and, focused as a protective film of glass lens mold. A Vacuum arc deposition, DLC is able to produce commercially, including ta-C. On the other hand, the vacuum arc plasma has a problem that the cathode emits a plenty of macrodroplets as well as ions and electrons. The macrodroplets deteriorates the film properties; uniformity, surface roughness, friction coefficient, hardness, etc. In order to overcome this droplet problem, the filtered arc method has been developed to remove the droplet from the plasma, as the most powerful method. However, the droplets emitted from the graphite cathode are in solid phase so that the conventional filtered arc system is hard to filter them. The one of authors has been developed the T-shape filtered arc deposition (T-FAD) system, in which the droplets are separated from the plasma at the 90 degree bent position. Though, the ta-C preparation to semi-spherical object was difficult by T-FAD until now. In this study, new preparation technique by T-shaped filtered-arc deposition (T-FAD) system has been developed for ta-C preparing to semi-spherical object.

First, number of droplets was reduced for capable large-aperture lens. A few droplets were attached film that prepared by T-FAD. Droplets were crash the duct wall, it was reflection and exploding, and it was flied to the substrate. Therefore, substrate position was set in the line of sight non-visible from the duct wall by controlling the plasma beam deflection. As a result, it was improved removing droplets performance. Plasma beam was deflected at about 15° upward from the horizontal line of duct exit, number of droplets was one-third.

Second, plasma beam was irradiated on normal axis of the substrate for uniform film thickness. So, we developed a multi-motion substrate holder which is able to move in direction of vertically and rotatory. Ta-C was coated to object simulated semi-spherical object, the film thickness distribution was confirmed. So, α is the angle between the normal axis of object and plasma beam center line. α is 0° (downward of object) and 40° (upward of object). A swing motion pattern in the vertical direction was programmed under the distribution of film thickness. As a result, uniform thickness ta-C film was coated on polished semi-sphere object in this condition, a uniform coating of the semi-sphere object was realized.

A ternary transition metal carbide of Cr₂AlC, also referred to as MAX-phase, is known to exhibit both the properties of metals and ceramics, providing high stiffness, high hardness, high oxidation resistance, thermal-shock resistance, and machinability. Due to the unique mechanical and chemical properties, Cr₂AlC is a promising candidate for protective hard coatings on tools or components operated in severe mechanical and thermal load conditions.

Growth of BN at high temperature (1500-1800°C) on various substrates (lab-made AlN templates on c-sapphire and c-sapphire alone) in a cold wall HTCVD reactor has been studied using NH3 and BCl3 as nitrogen and boron sources, and H2 as carrier gas. The experiment set-up consists of a vertical water-cooled quartz reactor with a graphite susceptor covered with AlN and heated by induction. Temperature of the substrate, N/B ratio in the gas phase and reactor pressure influence on the growth layer has been investigated. As-grown BN layers have been characterized by Field Emission Scanning Electron Microscopy (FE-SEM), X-ray diffraction (XRD) and Raman spectroscopy.

The study shows that the t-BN phase is systematically obtained at high growth rates as expected, whatever the temperature in the range investigated. To stabilize the h-BN growth on hetero substrate, a very low partial pressure of BCl3 should be used, leading to very low growth rates.

[1] M. Chubarov, H. Pedersen, H. Högberg, V. Darakchieva, J. Jensen, P.O.Å. Persson, A. Henry, Phys. Status Solidi RRL 5 (2011) 397.

[2] G. Younes, G. Ferro, M. Soueidan, A. Brioude, V. Soulière, F. Cauwet, Thin Solid Films 520 (2012) 2424.

In this contribution, microstructure and properties of Ti_1-xAl_xN coatings with x > 0.9 prepared using moderate temperature chemical vapour deposition are described. The coatings characterization was performed by X-ray diffraction and transmission electron microscopy techniques. The coatings consisting of fcc-Ti_1-xAl_xN, fcc-TiN and hexagonal AlN phases exhibit a special nanolamellar microstructure and an extraordinary high oxidation resistance up to 1.100 °C (air / 1h), which is considerably higher than it is known for Ti_1-xAl_xN- and even Cr_1‑xAl_xN grown by physical vapour deposition techniques.

The performance and tool lifetime of cemented carbide tools (WC:Co) can be significantly improved by chemical vapor deposited thin film diamond (CVD diamond). As the cobalt binder of the cemented carbides leads to graphitization during diamond deposition, the tools are usually pretreated by chemical etching procedures which remove the cobalt binder from the boundary zone of the tool substrate. This pretreatment may have a detrimental effect on the mechanical integrity of the tool and is highly time-consuming and costly.

A promising method to achieve good adhesion of diamond films on cemented carbides is to deposit a carbide interlayer, such as silicon carbide. This interlayer acts as a diffusion barrier and thereby protects the diamond film against the cobalt binder phase. The interlayer strategy is not only beneficial for the properties of the layer system but also reduces costs and time effort during tool coating. Furthermore, these interlayers enable to deposit diamond on cemented carbides with higher cobalt content than the conventional 6 to 10 wt-%.

Investigations on hot-filament activated chemical vapor deposited (HFCVD) SiC/diamond systems were performed without chemical etching of the cemented carbide tools with Co content of 6‑13 wt-%.

Tetramethylsilane (TMS) was used as a precursor gas which delivers both silicon and carbon species. Diamond and silicon carbide were deposited in separate coating processes (ex-situ). An in-situ deposition of both silicon carbide and diamond coating in the same batch will be developed by performing experiments on optimization of the SiC coating and on diamond in‑situ nucleation.

The performance of the tools coated with SiC interlayers and CVD diamond was tested in cutting tests as well as in model wear tests. The turning tests on the workpiece material AlSi17Cu4Mg, with regard to the tool life and wear form, were conducted without any coolant. The results of the experiments were compared with conventional CVD diamond tools. Additionally, the wear mechanisms adhesion, abrasion and surface fatigue of the innovative coating systems were investigated in model wear experiments.

The study was focused on the development of AlCrN hard layers for high speed machining applications since during the last years, it was proved that commercially available coatings present high abrasion and oxidation resistance over 800°C, thus increasing the tool lifetimes. Recently, the addition of alloying elements such as silicon, tungsten and boron are believed to be suitable for enhancing the oxidation resistance at high temperatures, as reviewed by many authors [1, 2].

In this study nitride-based coatings have been deposited by vacuum cathodic arc deposition (CAD). This technique has been chosen due to its versatility, allowing easily the industrial up-scaling.

The results were discussed taking into account the role played by the stratification and the silicon and oxygen content in AlCrN coatings. It is believed that surface and bulk oxides are sufficiently plastic to sustain abrasive wear at high temperatures without spalling effects [3]. Moreover, they are supposed to increase the wear resistance as they reduce the friction coefficients [4].

Arc evaporation is a powerful process for the deposition of very hard nitride coatings due to the high ionization rate of the discharge which allows a tuneable control of the impinging species energy. In particular, this technique is suitable to improve machining efficiency of carbide tools. Both mono- and nano-layer coatings based on Al, Ti and Cr nitrides have already been involved to coat machining tools.

In this paper, we first describe the industrial prototype used for the deposition of nitride single or nanolayer coatings. This device allows the deposition of nano-layer coatings with periods if about 5 to 50 nm by controlling the rotation speed of the triple-rotation substrate holder.

The structural, mechanical and tribological characteristics of different nitride coatings such as (Al,Cr)N, (Al,Ti)N monolayers and TiN-CrN, (Al,Ti)N-TiN, (Al,Cr)N-CrN nano-layers are then presented in relation with the coatings their deposition.

Finally, instrumented machining tests are performed using carbide tools coated with those different coatings to compare their ability to high speed machine several hard materials.

CrN/TiN multilayer coatings with different bilayer periods (l)were synthesized by using the combination of modulated pulsed power magnetron sputtering (MPPMS) and pulsed dc magnetron sputtering (PDCMS) in a close field unbalanced magnetron sputtering system. The structure and properties of the coatings were investigated by means of X-ray diffraction, transmission electron microscopy, nanoindentation and ball-on-disc wear test. The corrosion resistance of the coatings was evaluated by anodic polarization measurement in 3.5 wt% NaCl aqueous solution. The coatings showed face centered cubic nanolayered structure. Although no oriented TiN or CrN layer were prepared as an adhesion layer prior to the coating depositions, the coatings with relatively large l (e.g. 8.9 nm and 13.5 nm) exhibited a dominated (111) texture, while the coatings with relatively small l (e.g. 4.7 nm and 2.2 nm) exhibited a strong (200) peak. With a decrease in the l from 13.5 to 2.2 nm, the hardness and the elastic modulus of the coatings increased and achieved the highest values of 22.8 GPa and 276 GPa at a l of 2.2 nm, respectively. The anodic polarization curves of CrN/TiN multilayer coatings in a 3.5 wt% NaCl aqueous solution showed excellent pitting corrosion resistance with an increase in corrosion potential and a decrease in passive current as compared with untreated AISI 304L substrate.

Key words: CrN/TiN; Modulated pulsed power (MPP); High power pulsed magnetron sputtering (HPPMS); Pulsed dc magnetron sputtering (PMS); Multilayer coatings; Corrosion

TiAlN has been used as an effective protective coating for cutting tools since the 1980’s. Recently and triggered by the demands for improved high temperature protection, research on different alloying concepts have been explored, e.g. Cr-TiAlN and Y-TiAlN. Some of these alloy compositions have shown improved high temperature properties and better cutting performance. Here we build on this concept and explore the Zr-TiAlN system and to systematically investigate how Zr-additions to TiAlN affects thermal stability and hardness. The background for choosing Zr as the alloying element is ab initio calculations of the Gibb’s free energy of mixing that points out the possibility to tailor the driving force for spinodal decomposition though Zr-additions.

For this study we have used Ti₅₀Al₅₀N as the reference material and then added Zr resulting in the following compositions: Ti_0.44Al_0.40Zr_0.17N, Ti_0.25Al_0.24Zr_0.51N, Ti_0.09Al_0.07Zr_0.84N, and Ti_0.04Al_0.04Zr_0.92N. The coatings were deposited on hard metal (WC-Co) substrates with cathodic arc evaporation. After deposition the coatings were isothermally annealed for two hours at 800°C, 900°C, 1000°C and 1100°C respectively.

X-ray diffractometry shows that Ti_0.44Al_0.40Zr_0.17N decomposes isostructurally into cubic (c)-TiZrN and c-AlN, which is consistent with theoretical predictions. It also shows the unstable nature of this composition resulting in a driving force for spinodal decomposition. As a consequence of the decomposition age hardening occurs at 800°C. In contrast, for high additions of Zr, i.e. Ti_0.09Al_0.07Zr_0.84N and Ti_0.04Al_0.04Zr_0.92N, no decomposition occurs at the investigated temperatures. Instead the alloys remained in their original cubic state after annealing. This result is also in agreement with the theoretical predictions, which indicate a very weak driving force for decomposition for these compositions. Instead the heat treatments resulted in an annihilation of the lattice defects present from the deposition and a significant drop in hardness already after 900°C of annealing.

The diamond-like carbon (DLC) film has been widely used for molds and components protection in automotive and aerospace industries with its high hardness, low friction coefficient, high wear resistance, and chemical inertness. For medical applications such as the protective coating for artificial implants, typical DLC films are suffered by concentrated corrosion at pin holes and associated corrosion cracking which leads to the premature implant failure. In this study, the improved DLC film was synthesized by using the high power impulse magnetron sputtering (HIPIMS) technology to assess the feasibility of producing a pin-hole-free, low internal stress, and chemically stable DLC coating by the characteristic HIPIMS high energy plasma impingement during the coating process. The HIPIMS deposited DLC coatings were characterized for structural integrity and tribological behaviors. Additional in-vitro test, which emulates the actual bio-chemical and mechanical conditions, will be conducted.

Alumina (Al₂O₃) is being studied as a radiation resistant coating for various applications. The surface modification and irradiation effects on aluminum alloy 7407 after coating with alumina (Al₂O₃) was carried out using electrochemical and sol–gel method. Alumina coatings, synthesized by a sol–gel route, were deposited on Al7407 substrates by spin coating. Other series of samples were prepared electrochemically by varying DC voltage in the range 1 – 5 volts. Coatings are optimized by controlling various deposition parameters. For comparison purposes RF Magnetron sputtering technique is also used. The various characterization results indicate that relatively smooth coatings can be achieved by simple and scalable techniques such as electrodeposition and sol-gel. Coated substrates were then irradiated with Ni⁺, H⁺ and Ar⁺ ion beams by using Pelletron accelerator at several KeV to a few MeV. The nature and fluency of ions was varied to correlate to different environments. The surface modifications and structure of the coated surfaces before and after ion beam irradiations were characterized by FTIR, XRD, SEM, AFM and XRD, whilst the mechanical properties of modified surfaces were determined using nano-indentation. The results showed that the alumina xerogel films coated on the Al7407 substrates are successfully converted into crystalline alumina ceramic coatings by ion beam irradiations. Electrodeposited alumina films also show recovery and improved crystalline structure after ion beam exposure. Structure of resulting coatings is observed to be strongly depending on the ion beam types and dose conditions. By increasing dose intensity of Ar⁺ and Ni⁺ ion beams, γ-Al₂O₃ was observed which transformed to α-Al₂O₃ at higher energy. Nano-indentation results reveal that significant improvement in hardness and Young's modulus of the alumina -coated surface at optimized conditions can be achieved even after recovery from irradiations.

Tetragonal zirconia (ZrO₂) ceramics find a useful application in human dentures for reconstruction and filling purposes because of their unusual combination of strength, fracture toughness, hardness, and low thermal conductivity. These attractive characteristics are largely associated with the stabilization of tetragonal phase through alloying with aliovalent ions. The high fracture toughness exhibited by many of zirconia ceramics is attributed to the tetragonal to monoclinic phase transformation and its release during crack propagation. However, tetragonal phase of zirconia is not stable at room temperature. A number of ways are being sought, and we are investigating Fe₂O₃ addition in ZrO₂ for stabilization purposes. RF magnetron sputtering and Sol-Gel techniques have been used for preparation of the coatings, whereas XRD, SEM/EDX, AFM and IS techniques are used for characterization purposes. The optimized conditions are shown to lead to a stable tetragonal phase of ZrO₂ at room temperature. In sol-gel synthesis temperature, pH, nature of solvent and synthesis conditions played critical role in the size reduction and stabilization of zirconia at room temperature . ZrO₂ and Fe₂O₃ targets were used to prepare coatings by RF sputtering. Layer by layer growth of ZrO₂ and Fe₂O₃ was optimized for the preparation of stable zirconia coatings. Post annealing was done to investigate the alloys conditions and properties. X-ray diffraction (XRD) results show formation of tetragonal phase at 300^oC when sample was heated for 60 minutes. Coatings, prepared by sol gel, at 500^oC exhibit crystallite size as low as 11 nm as revealed by XRD results, whereas grain size ~30 nm was observed by scanning electron microscopy (SEM). Vickers Hardness measurements showed ~564 HV hardness of ZrO₂ samples prepared by sol-gel. Thus, sol-gel has proven to be a low cost, reliable and application oriented technique for the preparation of ZrO₂ coatings.

Thin films of copper indium gallium aluminum selenide Cu(In,Ga,Al)Se₂ (CIGAS) are prepared by sequential elemental layer deposition in vacuum at room temperature. The as-deposited films were heated in vacuum for compound formation. These films were concurrently studied for their structural properties by X-ray diffraction (XRD) technique. The XRD analyses include phase transition studies, grain size variation and microstrain measurements with the reaction temperature and time. It is also seen that the compound formation starts at 250^oC, with ternary phases appearing at 350^oC or above. Whereas, there is another phase shift, at 450^oC, with preference to the quaternary and / or pentenary compound. CdS is used as a window layer for the solar cell fabrication, whilst zinc-aluminate has been used as transparent conducting layer. The current-voltage results, at various illumination levels, are used to calculate the internal and external parameters of these solar cells; the internal parameters being obtained by a simple one-diode fitting of the experimental data. A maximum efficiency of around 9% is reported with a poor fill factor of 60%. Analytical calculations have also been performed and the analytical results point out towards loss of fill factor due to high series resistance.

CrC–NiCr coatings have been extensively employed in high temperature applications and automotive industries to improve high temperature corrosion resistance of component surfaces, improve their wear resistances and decrease the friction coefficient between varying sliding parts. With the recent technological advancement in the mining industries and the need to develop improved materials for the varying harsh mine environments, the need to investigate the tribological and corrosion behaviour of these coatings in both dry and wet environments, typical of mine conditions is very imperative. The present study described and compared the corrosion and tribological properties of HVOF sprayed coatings from two types of CrC-40NiCr feedstock powders and WC-40NiCr powders. Reciprocating sliding wear test was performed using the CETR UMT-2 test system under a load of 25 N and sliding velocity of 0.4 mm/s for 1000 seconds while wet abrasion test using the same wear parameters as well as electrochemical behaviour of the coatings were carried out in synthetic mine water environments. The morphology and microstructures present from the as sprayed, polished cross-section, wear and corroded coatings were examined using FE-SEM while the different phases present where analysed by XRD. The microhardness value was obtained using Vickers microhardness tester at a load of 100g. Hardness value obtained from the WC-NiCr coating is significantly higher than that of CrC-40NiCr. Results obtained from wear analysis showed that WC-NiCr coated steel substrate gave a higher wear depth of 0.93 mm when compared to CrC-NiCr 0.7 mm and this could be attributed to the presence of WC in the coating and also the use of WC ball which is a harder phase carbide than CrC. From the corrosion results, there is no much significant difference in the E_corr and I_corr observed. However, CrC-NiCr coatings showed more corrosion resistant with a negative shift in I_corr.

The present study explored the in-situ deposition of TiCrN/NiMnSb thin film heterostructures using magnetron sputtering. Room temperature nanoindentation was performed to obtain the mechanical and damping properties of these heterostructures and results were compared with pure NiMnSb films. A significant improvement in the hardness and elastic modulus was observed in TiCrN/NiMnSb films, which is due to the presence of superhard TiCrN thin layer. Creep and Impact test performed using berkovich and spherical indenter revealed better damping in surface modified NiMnSb ferromagnetic shape memory alloy (FSMA) thin films. The improved damping in surface modified FSMA was attributed to the good adhesion and strong combination of TiCrN and NiMnSb damping layers. The novel TiCrN/NiMnSb heterostructure with enhanced mechanical and damping properties would be a potential material for vibraton damping applications in MEMS.

Hollow cathodes are widely used for a variety of applications from intense light sources to for thin film deposition. The particular characteristics of the hollow cathode are that the geometry reduces the loss of electrons by the oscillative motion them between the sheaths on each side of the cathode, with this resulting in the production of high density plasmas. Sputtered atoms from the cathode normally travel from one wall to the other but can be carried toward the substrate through the use of a high gas Ar flow and this can be used to control the deposition rate. It has also been reported that under high pressure operation, the high density plasma can be used to generate nanoparticles in the gas phase; diameters in the range of 10-50 nm. We have developed a new version of the traditional hollow cathode based on the cylindrical planar design. The geometry is similar to a toroidal electrode which is open at the interior surface. In this way the “hollow” discharge occurs between the upper and lower electrode surfaces and the only way that electrons can leave the discharge is via the upper or lower apertures. We have studied the electrical characteristics of the discharge as a function of the applied electrical power and gas pressure, and we have used the system to deposit thin films as a function of the plasma power and gas flow. This hollow cathode was also successfully used to deposit thin films of nanoparticules of bismuth. By varying the different operating parameters, such as pressure (6.7 – 267 Pa), power (40 -120 W) and gas flow (20 – 120 sccm), it is possible to control the size of the nanoparticles (10 – 150 nm), as well as it is possible to control the deposition rate (0.4 – 4.0 nm/min) and the size particles with the applying of a bias (60 – 240 V) to the substrate.

The size and morphology of the nanoparticles were measured by SEM images. X-ray diffraction and XPS were used to determine the structure and composition of the deposits.

This study evaluates the performance of magnetron-deposited Cr- and Al-doped TiSiCN coatings, which were previously reported to have an excellent tribological properties, enhanced thermal stability and high-temperature oxidation resistance. Here, the behavior of these coatings during scratch tests, dynamic impact and electrochemical tests was studied and compared with that of the TiCN and TiSiCN reference coatings. The structure, elemental and phase compositions of coatings were studied by means of X-ray diffraction, scanning electron microscopy, and glow discharge optical emission spectroscopy. The coatings were characterized in terms of their hardness, elastic modulus, elastic recovery, and adhesion strength. To evaluate their electrochemical characteristics, the coatings were tested in 1N H₂SO₄ and 0.9% NaCl solutions. The coatings were also subjected to a range of impact tests, first in air, and then in normal saline (to assess a tribocorrosion effect) and distilled water (to assess a hydrodynamic effect in liquid). Under dynamic impact load, the coatings showed different impact resistance improving along the row TiCN→TiSiCN→TiCrSiCN→TiAlSiCN. In air, the TiSiCN, TiCrSiCN, and TiAlSiCN coatings endured a dynamic impact force as high as 1000 N with a minimum impact wear observed for the TiCrSiCN and TiAlSiCN coatings. The accelerated degradation of the TiCN, TiSiCN, and TiCrSiCN coatings in distilled water and normal saline was attributed to both the NaCl-induced corrosive processes and hydrodynamic effect resulting in accelerated abrasive wear. The TiAlSiCN coating was the only sample to sustain a repetitive impact load of 500 N for 10⁵ cycles both in distilled water and normal saline.

In recent years, great attention has been devoted to the development of a new class of thin films with a special structure and unique properties against thermal stability and wears damage. The high metastability of the amorphous structure is the most striking aspect of ternary nitride alloys and is one of the reasons for their successes as thin-film diffusion barriers in semiconductor metallization technology.

Zirconium tungsten nitride (Zr_xW_1-xN_y) nanocrystalline films represent a new class of ternary metal nitride coating material. In the present work, films were deposited onto Si substrates using DC/RF reactive magnetron sputtering. The temperature dependence of the structure, morphology, stability and mechanical properties have been studied of the films under two different conditions; (i) Films have been deposited in-situ at various substrate temperatures (room temperature ~ 30⁰C to 600⁰C). (ii) Ex-situ annealing have been done up to 600⁰C in the ambient atmosphere of films deposited at 30⁰C. It was found from the first kind of treatment that (i) there is a strong correlation between crystallization and deposition temperature and (ii) the thickness and hardness of the films have dual trend depending on the phases present in the films. (iii) the maximum hardness achieved is ~ 25 GPa of the films deposited at 300⁰C, while,the outcome of lateral treatment were (i) No significance of oxide phase formation except the broadening of hump.(ii) The O₂ start to incorporate above 200⁰C with increasing tendency up to 600⁰C. (iii) The RMS roughness (δ_rms) and thickness of the films increases with annealing temperature (iv) The hardness decreases (~11GPa) as the percentage of O₂ increases in the films.

TiN and TaN coatings widely used due to excellent mechanical and tribological properties. Specifically, TiN/TaN multilayer coatings have been exhibit superior mechanical and chemical properties, such as hardness, adhesion and wear resistance, when compared to single layer nitride coatings. Therefore, in recent years, multilayer coatings composed of two kinds have been investigated. For this reason, in this study, TiN/TaN multilayer films were deposited on Mo-alloy substrate and Cu-alloy substrate by Closed-Field Unbalanced Magnetron Sputtering (CFUBMS). The structural and mechanical properties of these films were analyzed by using XRD, SEM and microhardness tester, respectively. The adhesion and fatigue properties of the coatings were evaluated via a scratch test in two modes. A sliding-fatigue multimode operation was used that involved multi-pass scratching in the same track at different fractions of the critical load (unidirectional sliding), and a standard mode with progressive loading was also utilized. Adhesion and fatigue properties of TiN/TaN multilayer coatings deposited on different substrates were discussed according to microscopic image examinations of the scratch tracks.

Key Words: TiN, TaN, multilayer films, CFUBMS, adhesion, fatigue

TaN–(Cu,Ag) nanocomposite films were deposited by reactive co-sputtering with Ag/Cu=6.5/3.5 in atomic %. The total amount of soft metal contents is 7 and 11 at.%. After PCA, the films were characterized using XRD, FESEM, nano-indentation. The tribological properties and antibacterial behaviors were also examined. The results show that the increase of pulse frequency and the reduction of ON/OFF ratio would enlarge substrate-film temperature difference. Therefore the substrate could be protected better. Through the anti-wear and anti-bacteria studies, it was found that the film/substrate system, after PCA, could maintain low frication and low wear rate, and high antibacterial efficiency against E. Coli. All these properties were related to pulse frequency and ON/OFF time ratio.

Recently, zinc oxide (ZnO) thin films have attracted increasing attention due to their excellent properties and their potential applications in various fields; gas sensors, piezoelectric devices, transparent conductive electrodes …. The performance of ZnO coatings in a number of modern devices and especially as gas sensors is strongly linked to their specific surface that can be tuned by controlling their morphology. ZnO nanostructures such as nanowires/nanorods, nanobelts, and nanodots are the object of intensive studies. Most of nanostructured ZnO materials are synthesized by vapour transport based on vapour–liquid–solid (VLS) growth mechanism using a noble metal as catalyst such as Au and Cu. However, some studies show that Au is not necessary for nanowire growth. Among the different deposition methods, the technique used in this study is the reactive magnetron sputtering.

In this paper, we investigate the feasibility of ZnO coatings with different morphologies (dense, porous, nano-wire and nano-tree) by reactive magnetron sputtering. After a short description of the experimental devices used for the deposition stage and the hydrocarbon sensing bench, a first part will be dedicated to the chemical, microstructural and structural characterization (SEM, XRD,…) of coatings in relation with their deposition parameters. We will the report the performance as dodecane-sensors of ZnO coatings with different morphologies as a function of dodecane concentrations and sensor surface temperature.

TiAl6V4 and other titanium alloys are high-performance alloys used for lightweight and high strength applications due to their low density (ρ_Ti = 4,51 kg/dm³) in combination with a high yield strength of about 1’000 MPa. However, titanium alloys are considered as difficult to machine materials due to their high strength, the low Young’s modulus, the low thermal conductivity and the high tendency to sticking during the cutting process.

The present work shows how the lifetime and productivity of a coated state-of-the-art thread cutter can be improved. Crucial for the tapping is to ensure a reliable process, since the thread cutting in a component is usually one of the last machining steps conducted, and thus tool failure at this point would lead to the loss of an already highly valuable work piece.

The parameters used to optimize the performance of the reference tool were the cutting edge pre- and post-treatment as well as the coating type. Since first experiments showed that the sticking of titanium on the flank of the thread cutter is the lifetime limiting factor, a tribological experiment was used to evaluate the affinity of various nitrides, oxynitrides and DLC coatings to titanium. Measurements were done at 400°C on coated test plates against a TiAl6V4 pin and the build-up was then quantified using a profilometer. The results identified different behavior for the investigated coating types, which will be discussed and correlated to the cutting performance of the coated tools.

By selecting an appropriate coating as well as using optimized pre- and post-treatment the lifetime of the newly developed thread cutter could be more than doubled compared to the reference tool and further on this new generation tool was capable to work at faster cutting speeds in production.

Evaluation of the corrosion behaviour and the protective properties of Al-based PVD coatings in aqueous solution have been carried out by Salt Spray Testing (SST) and Electrochemical Impedance Spectroscopy (EIS). SST offers many advantages, including the fact that it is a standardised method for conducting exposure to a corrosive environment and evaluating the results. However, SST has been criticised for its lack of reproducibility from one test to another, and for failure to provide a quantitative measure of corrosion degradation. The EIS method is a well-established technique and a powerful tool to determine a quantitative, numerical value for corrosion damage of coatings, and to investigate the electrochemical reactions mechanisms of the corrosion process in a short period of time. Coatings produced by physical vapour deposition (PVD) techniques can increase the lifetime and service quality of the system. Two main objectives are taken into account in this study; firstly, to evaluate the corrosion behaviour of Al-based PVD coatings after SST exposure and in 3.5% NaCl solution at different exposure times, by EIS. Secondly, to obtain a correlation between SST and EIS test results for Al-based PVD coatings. SST experiments were carried out after exposure times of 24, 48,123, 216 and 384hrs for ten test panels of PVD AlCr coatings deposited at 300oC & 400oC. EIS experiments of PVD AlCr coatings deposited at 300oC & 400oC have been carried out after open circuit potential (OCP) stabilisation, as a function of the immersion time for 24, 48,123, 216 and 384hrs in 3.5wt% NaCl solution. EIS data was obtained using an electrochemical cell instrument and then the experiments is complemented by scanning electron microscopy (SEM), Energy Dispersive X-ray (EDX) composition analysis and phase analysis by X-Ray Diffraction (XRD).

Titanium and chromium nitrides were deposited by means of two high energetic deposition techniques such as cathodic arc deposition and high-power impulse magnetron sputtering (HIPIMS) [1,2].

The aim was to establish a correlation between these techniques and the resulting morphological-mechanical properties. Firstly, a physicochemical characterization was conducted employing X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), glow discharge optical emission spectroscopy (GDOES) techniques.

Subsequently, the mechanical-tribological characterization allows the comparison of the different chemical-morphological properties. The resulting properties were strongly depending on the processing routes and their specific parameters. For instance, the differences in terms of surface roughness affected the final tribological properties.

The built-up of material at the edge of the wear tracks found after ball-on-disc tests is in good agreement with higher droplets’ density. Indeed, the better surface state (no droplets) in the case of HIPIMS leads to the reduction of the coefficient of friction (COF). It is well known that macroparticles emission creates defects (droplets) in non-filtered cathodic-arc evaporation processes. These droplets act as cutting edges, thus increasing the COF as reported by several studies [3].

Taking into account that until now, HIPIMS has few industrial applications, a final aspect concerning the industrial up-scaling feasibility was investigated. To accomplish this aim, several aspects such as the deposition rates and the measured final properties were considered. Finally, the machining performances on the developed coatings were measured, in order to justify the advantages of HIPIMS if compared with the cathodic-arc process.

References

[1] F. Sanchette et al. Surf. Coat. Technol. 205 (2011) 5444.

[2] A.P. Ehiasarian et al. Surf.Coat. Technol. 163-164 (2003) 267.

[3] O. Banakh et al. Surf.Coat. Technol. 163-164 (2003) 57.

Shape memory alloy (NiTi) thin films coupled with graded AlN/Al multilayers produce an intelligent material having improved mechanical and tribological properties. In the present study [AlN/Al]_n/NiTi/Si heterostructures have been deposited on Si substrate using magnetron sputtering technique. AlN/Al multilayers were grown on NiTi/Si in a graded pattern with bilayer period n=1, 4, 8 & 12 and the effect of bilayer period on different properties of heterostructure was evaluated. The heterostructures were characterized in terms of structural, electrical, morphological, mechanical and tribological properties by X-ray diffraction (XRD), four probe resistivity method, atomic force microscopy, field emission scanning electron microscopy, nanoindentation, and scratch tests. The bilayer period of AlN and Al had great influence on the hardness and the toughness properties of the heterostructure. This enhancement in hardness and toughness of the heterostructure could be attributed to the different mechanisms for layer formation with nanometric thickness such as the Hall–Petch effect and the number of interfaces that act as obstacles for the crack deflection and dissipation of crack energy.

Keywords : NiTi, Magnetron Sputtering, Shape memory, Nanoindentation

Plasma immersion assisted deposition (PIAD) is an effective deposition technology for synthesising high quality carbon thin films. A graded layer structure which can mitigate delamination and improve adhesion can be achieved by this combined implantation and deposition technique. Hydrogen containing diamond like carbon (a-C:H) films exhibit an ultra-low sliding coefficient of friction (CoF) in dry or inert (e.g. vacuum) environments; however, the CoF of a-C:H changes dramatically with increasing humidity. Silicon-doped a-C:H (Si-DLC) films can show better humidity adaptability compared with a-C:H films. In this study, diamond-like carbon films with different silicon doping contents were deposited by PIAD with different experimental parameters. Nano-indentation and impact testing were used to investigated the mechanical properties e.g. hardness, elastic modulus and adhesion of Si-DLC coatings. Pin-on-disc wear tests were applied in an environmental chamber with humidity control, to examine the friction and wear properties at different RH% values. The chemical compositions are also examined by Energy Dispersive X-ray (EDX) analysis and Raman Spectroscopy.

Based on the first-principles calculations, the properties of TiAl(Zr, Hf)N system have been systematically investigated and the calculated results are compared with the available experimental data. The predicted structural, phonon, electronic, and thermodynamic properties of cubic binary nitrides MN (M= Ti, Al, Zr and Hf) can give an accurate prediction for the high temperature thermodynamic properties, especially for the thermodynamic data which are difficult to determine by experiments. The temperature dependence of elastic constants are computed for the first time by first-principles quasiharmonic approach and efficient stress-strain method and is beneficial to the determination of residual stress of coatings. The effects of both lattice vibration and pressure on the thermal decomposition of TiAlN, ZrAlN and TiZrN have been first considered in the present work. It is found that the pressure increasing make the temperature of predicted binodal and spinodal curves increase, while the vibration contribution significantly decreases the temperatures. In addition, the study indicates that the improved age hardening of cubic Ti-Al-N coatings by adding Zr is because of the enlarged composition range of binodal and spinodal curves. Finally, the quaternary SQS models have been developed in the present work to describe the disordered solid solution, based on which the mechanical properties of Ti-Al-Zr-N and Ti-Al-Hf-N coatings are calculated. Additionally, the effect of addition of Zr and Hf on the spinodal decomposition is studied. It is concluded that Zr and Hf are effective in influencing the age-hardening as they promotes the coating spinodal decomposition. Present work allows the combination of theoretical predication and experiment research, which provide the theoretical guidance and useful information for the further research of coatings system.

Magnesium is a promising engineering material with a high strength-to-weight ratio which enables lighter products to be achieved. Moreover, the excellent castability and weldability of magnesium alloys contribute to this material’s suitability for prospective markets in the construction, automotive, aerospace and communications industries. However, several undesirable properties of magnesium alloys have prevented their widespread adoption; these include insufficient resistance to creep and poor corrosion and wear resistance.Depositing protective coatings onto magnesium alloy parts is an effective strategy to improve the corrosion and wear performance. In this work, duplex surface treatments incorporating novel PVD techniques are used to explore the wider application of magnesium alloys. To improve the durability of low-strength Mg-alloy products in tribological applications, a relatively soft and compliant, amorphous interface layer (rather than the hard – and brittle – AlMg intermetallic compound-containing layers so far explored in the literature), containing B, N, Zr, Ti or Cr elements (as well as Al), is deposited by plasma-assisted PVD. The introduction of an amorphous and/or nanocrystalline interface, with an elastic modulus closer to that of the underlying Mg-alloy substrate, accommodates substrate strain more effectively. In addition, on top of the interface layer, ceramic coatings such as TiN, CrN (or plasma electrolytic oxidation post-treatments) can be deposited to increase the hardness and corrosion resistance of the surface. Compared to hard coatings deposited directly onto Mg-alloy substrates, this design philosophy improves the matching of coating/substrate interfacial mechanical properties, such that coating toughness is enhanced by accommodation of the deformation energy without fracture. Overall, we show that such duplex layered treatments have potential to provide improved wear and corrosion protection to Mg-alloys.