ICMCTF2014 Session BP: Symposium B Poster Session

About solid lubricant development for aerospace application, three issues are crucial to obtain good tribological performance: wear resistance related with fretting during the satellite launch, high adhesion on the substrate, and high lubricant life associated with low friction coefficient environment (less than 0.3) and its resistance in atomic oxygen.

This paper presents comparative studies on amorphous diamond-like carbon (DLC) containing silver nanoparticles (DLAg) and Silicon oxide bonds (DLSiO) obtained via automated plasma enhanced chemical vapor deposition (PECVD) using methane, silver cage, and Hexamethyldisiloxane, as carbon, silver, and silicon precursors. The films were produced in order to obtain repeatability and traceability on tribological behavior for aerospace use associated with high corrosion resistance in atomic oxygen atmosphere.

The DLAg and DLSiO were deposited on titanium alloy surfaces and the growth parameters (work pressure, temperature, discharge power, and duty cycle) were controlled to guarantee repeatability and traceability of the films. Friction, wear and adhesion tests were run out in a Bruker Tribometer. The corrosion resistance was evaluated by atomic plasma oxygen etching and chemical structure degradation was analyzed with Raman spectra.

Production research for industrial coatings from thermochemical processes plays an important role in materials science. Thermoreactive Diffusion deposition technique (TRD), to obtain homogeneous, continuous and resilient coatings for a simple procedures at cost.

The coating was deposited in gray iron pearlitic matrix with randomly distributed lamellar graphite and 3.5% total carbon percentage. The process was carried out in a salt bath of molten borax at 940 °C for 2 to 5 hours. Ferro-niobium is used as the carbide-forming element and aluminum as the reducing agent.

Microstructure and wetting character of radiation exposed hydrogenated amorphous carbon (a-C:H) films were evaluated by Raman spectroscopy, by measuring their contact angle with water droplets and by calculating their surface tension. a-C:H films were deposited by plasma enhanced chemical vapor deposition (PECVD) at room temperature from pure acetylene (C₂H₂) gas used as carbon and hydrogen atoms precursor. Samples were exposed to ultraviolet and gamma radiation and to alpha particles. They were analyzed as a function of the deposition pressure that ranged between 13 Pa and 400 Pa. Their microstructures were analyzed at two Raman excitation wavelengths, 514.5 nm and 1064 nm. Results show that the a-C:H structure is formed by a combination of sp and sp² carbon-carbon bonds and sp³ carbon-hydrogen bonds. Typical D and G bands at both excitation frequencies are presented in all spectroscopy data and different features could be observed depending on the Raman excitation energy. At green excitation an intermediate band between D and G bands and close to 1500 cm^-1 can be accessed. It is associated to sp³ carbon-hydrogen bonds. At 1064 nm a band close to 1850 cm^-1 is an evidence of the presence of sp carbon bonds. As-deposited a‑C:H film wetting character results show a very dramatic change in the contact angle between the surface and deionized water droplets. Samples deposited at C₂H₂ pressure as low as 26 Pa are hydrophilic, while those deposited at 400 Pa are super hydrophobic with contact angle above 160^o. Post deposition radiation changes the surface tension of all samples; although modifications are dependent on the radiation energy. It changes the surface structure of the samples, but the bulk microstructure remains the same.

Physical Vapour Deposition techniques, like magnetron sputtering or arc evaporation, are highly valued for industrial applications to synthesize hard protective coatings with superior performance. Generally, powder metallurgically prepared targets composed of e.g. metallic Al and Cr particles are used in a reactive nitrogen atmosphere to deposit Al_xCr_1-xN. For both deposition processes, the influence of various deposition parameters ─ like partial pressure, gas mixture, or temperature ─ on the coating performance is well investigated, but only little information is available concerning the impact of the target material itself. Therefore specially developed powder metallurgical prepared targets, with a comparable Al/Cr ratio, consisting of metallic Al and Cr, intermetallic Al₈Cr₅, and ceramic AlN and CrN powder were used to deposit Al_0.7Cr_0.3N films. Furthermore, due to the possibility to use a ceramic target material comparative investigations on the influence of a reactive (Ar/N₂ atmosphere) and non-reactive (Ar atmosphere) deposition were carried out. Detailed analysis of the resulting microstructure, mechanical properties as well as thermal stability and oxidation resistance indicate a strong influence of the different targets used. Changing from the metallic target materials to the ceramic-like target and from reactive to a non-reactive deposition process the preferred orientation of the Al_xCr_1-xN film can be altered from preferred (111) to (200). Further on, fracture cross sections indicate a more nano-crystalline-like morphology as well as a significantly increase in deposition rate from values between 11 and 16 nm/min to 23 nm/min, respectively, when using non-reactive deposition to prepare Al_xCr_1-xN. Hardness evaluations demonstrate that values around 25 GPa can be obtained when using the nitride target material, which is twice as high as for reactively deposited coatings from standard metallic Al/Cr targets using similar process parameters. Also, investigations on the thermal stability, especially with respect to the onset of Cr-N dissociation, indicate a clear shift of decomposition to higher temperatures for coatings prepared from optimized target materials.

A central subject of current protective coating development is the phase formation in low temperature physical vapour deposited, PVD, (Al_1-xCr_x)₂O₃ coatings. Experimental results have shown that magnetron sputtered or arc evaporated coatings synthesised at temperatures as low as 500 °C usually crystallise in an amorphous or metastable face centred cubic based phases, like the defect-spinel γ- or the B1-type. This is however in contradiction to ab initio phase stability predictions, which suggest the desired and industrially important corundum type solid solution α-(Al_xCr_1-x)₂O₃ to have lower energy of formation, thus being the stable phase and preferentially formed.

Within our investigations of three phases (corundum α, defect-spinel γ, and B1-like fcc) across all Al compositions, x, of (Al_xCr_1-x)₂O₃ we find that the α solid solution is more sensitive to randomly generated defects than the γ-type and B1-type. We propose that these findings in addition to exceptionally high surface energies for certain terminations of the corundum structure can explain the favoured formation of γ- and B1-(Al_xCr_1-x)₂O₃ during low temperature PVD processes, which generally lead to high defect densities and small crystallite sizes.

In this work thin films doped with cobalt were prepared by Metal – Organic Chemical Vapor deposition. Photocatalytic activity of TiO2 particles has been investigated extensively because of their strong oxidizing power, high chemical durability, and nontoxicity. It is well known that nanometer-sized anatase particles with high crystallinity have a high photocatalytic activity [1]. However, the absorption wavelength of anatase (λ≤385 nm) does not fit with the solar spectrum; the solar energy above 3.0 eV (λ≤410 nm) is less than 5%.

In this study, thin films of TiO2 doped with cobalt deposited on glass and silicon substrates were synthesized using the technique of vapor phase chemical deposition from metal-organic precursors such as titanium isopropoxide and cobalt acetylacetonate , the films were doped with different concentrations of cobalt 2 %, 4% 6 %, 8% and 10 %.

With the synthesis and characterization of our material is achieving a better understanding of the synthesis methodology also improved to some extent on the different physical and chemical properties of the material. The crystal structure of all prepared samples were characterized by X-ray diffraction to confirm the existence of anatase phase of TiO2; Raman spectroscopy results were complemented observing the characteristic vibrational modes of TiO2 in its anatase phase.

The morphology and growth of the films was characterized by electronic microscopy (SEM) observed a flower-like growth in all samples. Finally the optical characterization of the samples was performed by UV-Vis spectroscopy obtained with these results a value of bandwidth allowed for each sample obtained and the relationship between the amount of impurities in each sample and its improvement in their electronic properties.

References

[1] Tada, H., and Tanaka, M., Langmuir 13, 360 (1997) Anpo, M., Ichihashi, Y., Takeuchi, M., and Yamashita, H., Res. Chem.Intermed. 24, 151 (1998).

Nb-V complex carbide coatings were produced onto AISI D2 steel by the thermo-reactive diffusion (TRD) process to improve the surface hardness and corrosion resistance of this tool steel. The carbide coating treatment was performed using molten borax added with ferroniobium, ferrochrome and aluminum at temperatures of 1223, 1293 and 1363 K during 2, 3, 4 and 5 h. The coating layers were characterized by optical and Scanning Electron Microscopy Microscopy (SEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS) and X-ray fluorescence spectrometry (XRF). The coating growth rates were studied, and a kinetically model of the layer thickness as a function of the treatment time and temperature was established. The hardness of the coating was measured by nanoindentation and its resistance to corrosion was evaluated with electrochemical tests of potentiodynamic polarization. The carbide layers produced a homogeneous thickness as well as an improved hardness and corrosion resistance as compared to the uncoated steel.

Niobium-Chromium carbide coatings were deposited by thermo-reactive diffusion (TRD) deposition technique on three different tool steels (AISI D2, 1045 and H13). The carbides were obtained using salt baths composed of molten borax, aluminum, and ferro-niobium or ferro-chromium. All steels were treated through TRD process performed at 1020 °C for 4 hours. The thickness and morphology of the coatings were characterized by optical and Scanning Electron Microscopy (SEM) and the crystalline structure was studied through X-ray diffraction (XRD). Chemical composition was evaluated by energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Hardness of the coatings was measured by nanoindentation, and its wear resistance was studied by bole on disk test. The rate of corrosion was assessed with potentiodynamic polarization and the corrosion resistance was evaluated via electrochemical impedance spectroscopy (EIS) tests. The XRD results confirmed the formation of NbC and Cr_xC_y phases in all carbides. SEM results shows good homogeneity in the coatings thickness, and nanoindentation results showed that the coatings have higher hardness in comparison to the uncoated steel. XPS results indicated that the coatings are formed by carbides of chromium and niobium and the corrosion resistance is higher compared to the uncoated steel.

Atomic layer deposition (ALD) is a chemical vapor deposition (CVD) based method for growing thin films with high precision.¹ The growth proceeds through alternating and saturating surface reactions of two or more gaseous precursors. Because the precursors are pulsed in the reaction chamber alternately and separated by inert gas purging, excellent conformality even on high aspect ratio structures can be achieved. The films grow one atomic layer per cycle and thus both the thickness and composition can be controlled down to nm level. ALD thin films are known to have low defect density already at <10 nm thicknesses.

In the present work three types of ALD corrosion protection coating systems were studied on low alloy steel. Firstly, single 50 nm ALD coatings combining the excellent barrier properties of Al₂O₃ and chemical stability of Ta₂O₅ were considered. The aim was to optimize the coating structure for best sealing properties and durability. Secondly, a 10 nm filtered cathodic arc deposited (FCAD) film was grown under the optimized 50 nm ALD coatings. The FCAD layer homogenized the steel surface for a more ideal ALD growth, which led to improved protective properties. Thirdly, the conformality of ALD was utilized in sealing pinhole defects in physical vapor deposited (PVD) CrN coatings. The corrosion protection properties of the coatings were studied with electrochemical measurements (LSV and EIS) and neutral salt spray (NSS) testing. Additionally, the morphology and composition of the coatings were analyzed to gain insight into the protection mechanism. The ALD coatings had excellent barrier properties, reaching a decrease of three orders of magnitude in the corrosion current density of the steel. The long-term durability of the single ALD coatings was found to be insufficient but could be improved with the FCAD sublayers. Moreover, the NSS durability of CrN coated steel could be increased from 2 to 168 hours with ALD sealing.

[1] V. Miikkulainen, M. Leskelä, M. Ritala and R. Puurunen, J. Appl. Phys. 113 (2013) 021301

Crystalline PVD alumina coatings offer a high potential for application as protective coating material on cutting tools due to their high hot hardness, high chemical inertness, high thermal stability and good wear resistance. Especially over the last decade the High Power Pulsed Magnetron Sputtering (HPPMS) technology has gained a growing interest. This technology offers possibilities to improve the coating properties such as microstructure and mechanical properties.

In the first part of this work the hysteresis behavior of Al target sputtered in a HPPMS discharge and a Kr/Ar/O₂ mixture was investigated for various HPPMS pulse lengths (30, 50, 100, 200 μs) at constant pulse frequency and average power in an industrial scale unit. Cathode current and voltage were recorded for the different pulse lengths. In a second step, aluminum oxide coatings were deposited on cemented carbide substrates at a constant pulse length of 50 μs and various bias voltages (-100, -200 and -250 V). The coating thickness and morphology are determined using SEM (Scanning Electron Microscopy). Hardness and Young’s modulus were measured using nanoindentation. Phase composition was investigated by using XRD (X-ray Diffraction). Decreasing of pulse length from 200 to 30 μs at constant average power leads to a considerable increase of cathode current from 76 A to 468 A, respectively. It could be observed that the peak current has a strong influence on the amount of maximum allowable oxygen flow in the reactive process. Longer pulse lengths and so lower peak current allow a higher oxygen flow in the coating process compared to short pulses. The characterization of deposited coatings shows that at higher bias values a dense fine grained crystalline morphology is observed. However, a decrease of the deposition rate was observed with increasing bias from -100 V (1,26 μm/h) to -250 V (0,77 μm/h). Regarding the phase composition, peaks of crystalline γ-Al₂O₃ were detected for all deposited HPPMS aluminum oxide coatings.

Fracture toughness is one of the most important mechanical properties for both bulk and thin film materials. For bulk materials, fracture toughness can be easily measured through ASTM standard procedures. In contrast, fracture toughness measurement of thin films is still problematic. Many kinds of testing methods have been developed and used to evaluate the fracture toughness of thin films. Recently, our group proposed an energy-based method without using the external stress, but employed the residual stress as the stress source to induce cracking. The proposed method has been applied on both TiN and ZrN hard coatings, and the results showed that the fracture toughness of random-textured TiN hard coating was 16.5 that was a reasonable value compared with previous literatures. On the other hand, the results of ZrN hard coatings showed an anisotropic variation with crystal orientation. In this research, TiZrN ternary nitride film was chosen for a model material because TiZrN is a single phase material when deposited at temperatures lower than 500°C. According to Griffith criterion, fracture toughness is the release of elastic energy that can create two new surfaces of a crack for brittle materials, which is associated with atomic bonding energy of the fracture surface. In TiZrN thin film, the bonding energy may change with Ti/Zr ratio, and thus composition may strongly affect the fracture toughness. The objective of this study was to investigate the effect of composition on the fracture toughness of TiZrN hard coatings. TiZrN coatings with different Ti/Zr ratio were prepared by unbalanced magnetron sputtering. Following our previous testing method, residual stress was used as the stress source for the toughness measurement, which could be measured by the laser curvature method. For the proposed energy-based method, the average storage energy (Gs) was evaluated from the residual stress before crack initiation, and then the fracture toughness (G_c) of the TiZrN coatings can be obtained from Gs.

Keyword: Fracture toughness, TiZrN, residual stress

ZrO₂ is commonly used as a protective coating for metal substrates owing to its excellent corrosion resistance, while ZrO₂ coating is difficult to be deposited on the stainless steel because of the wettability problem. The purpose of this research was to overcome the wetting issue by producing ZrO₂ coatings on the stainless steel using ion plating or by heat treating ZrN coatings in vacuum. In this study, we used two approaches to deposit ZrO₂ films on stainless steel. One approach is to directly deposit ZrO₂ on stainless steel substrate using hollow cathode discharge ion-plating (HCD-IP) method, where the HCD-IP provided high ionization rate and solved the wetting issue. The other one was to deposit ZrN films on the stainless steel substrate, and then oxidize the ZrN films by heat treated the specimens in vacuum at 1000°C converting part of the ZrN to ZrO₂. The growth mechanisms of ZrO₂ are different in these two methods. In the former method, the ZrO₂ film grows in the way of the columnar grain growth from bottom-up direction. However, in the latter method, the ZrO₂ film grows inside the ZrN film from top-down direction and the ZrO₂ layer becomes nano-granular structure in the vacuum heat treatment. The 500-hr salt spray tests indicated that the ZrO₂ coatings produced by both methods shows excellent corrosion resistance. The corrosion resistance of the ZrO₂ films was further evaluated by AC impedance and potentiodynamic polarization scan. The AC impedance wa s undergone in the 1N H₂SO₄ and potentiodynamic polarization scan was carried out in 5% NaCl and in 1N H₂SO₄.

Due to their excellent mechanical properties, t itanium nitride (TiN) coatings have been widely utilized in tool industry as wear resistant and protective coatings. The usage of hard coatings can not only protect the substrate, but also significantly extend the service life of the products. The major requirements of wear resistant coatings are high hardness with substantial thickness, a least a few mm. However, with the increment of film thickness, the internal residual stress may accumulate, and lead to film spallation. The objective of this study was to deposit thick TiN coatings (> 5mm) on AISI D2 tool steel substrates without using Ti interlayer, and to investigate the influence of different processing parameters on wear resistance and mechanical properties of the coatings. TiN coatings were deposited on AISI D2 steel substrates using unbalanced magnetron sputtering at different deposition parameter s. The main controlling deposition parameter s to produce thick TiN coatings were the opening of gate valve between turbomolecular pump (TP) and deposition chamber and the pumping speed of TP. The flux of argon and nitrogen was at a fixed ratio. X-ray diffraction (XRD) was used to determine the preferred orientation of the TiN films. The hardness of the TiN coatings was measured using nanoindentation. The residual stresses of the TiN coatings were determined by cos²α sin²ψ XRD and laser curvature method. The adhesion between the coating and substrate was evaluate d by scratch test. The influence of deposition parameter on wear resistance of the coatings was evaluated using pin-on-disk wear test. By adjusting deposition parameters, we could successfully produce thick TiN films on D2 steel with low residual stress and superior wear resistance. In addition, the deposition process consumed much less energy than traditional processes, and therefore the results will be useful for industrial appl ications.

Keyword: titanium nitride, AISI D2 tool steel, wear resistance, micrometer size

Ternary TiZrN thin films were deposited by DC unbalanced magnetron sputtering from dual guns(Ti,Zr) targets onto Si (100) substrates. In this work, we investigate the effect of substrate bias on the structure and properties of ternary TiZrN thin films (exchanging bias from -20V to -100V). The substrate bias primarily affected the properties and structure containing hardness, preferred orientation, packing factor, etc. Consequently, substrate bias is a sensitive factor for process parameters of TiZrN coating. The crystal structure and preferred orientation of TiZrN films were characterized using X-ray diffraction (XRD). Experimental results indicate that the preferred orientation of TiZrN films is changed from (200) to (111) with increasing substrate bias. Zr adatoms are re-sputtered more easily than Ti adatoms during film growth. However, the experimental results show that Ti / Zr ratio did not vary obviously with different substrate bias. The crystallinity and packing factor, which associated with hardness, were enhanced by increasing substrate bias. TiZrN films had maximum hardness 32GPa as the bias voltage reached the critical value. Due to strengthening mechanism of the TiZrN are solid solution strengthening and grain boundary strengthening, the optimal solid solution strengthening effect(greatest inhomogeneous stain) can be obtained by controlling the ratio of Ti/Zr close to 1 for all the specimens. Both hardness and packing factor decreased as the bias voltage exceeded the critical value. Resistivity increased with increasing bias and with decreasing packing factor.

The objective of the study is to investigate effects of temperature on BiFeO₃(BFO)/FePt epitaxial bi-layers system structure. In this paper, we prepared the BFO (10 nm) / FePt (10 nm) thin films epitaxially grown on (111) SrTiO₃ (STO) single crystal substrates and systemically study effect of deposition temperature of FePt. The formation of epitaxial films structure was confirmed from the x-ray diffraction and (00L) Bragg reflection of x-ray. A slight partial relaxation of out-of-plane strain in epitaxial systems was observed. Synchrotron radiation XRD results display c lear six fold symm etries and (111) FePt/BFO films by using (111 ) azimuthally sc an, unambiguously indicating that the present samples are epitaxially thin films. Large exchange bias of 150 – 360 Oe at room temperature were obtained for the epitaxial (111) FePt (10 nm)/BFO (10 nm) films at different growth temperatures (400 – 700 ºC). The exchange bias for the samples grown on (111) STO subs trate is high er than those of samples deposited on (100) STO substrate. An intuitive and reasonable explanation for this discrepancy is the surface spin configuration of BFO layer, because BFO (111) has an uncompensated surface and (001) has a compensated surface. With regard to temperature of FePt, there have exchange bias for the samples with FePt temperature below 600 ºC. As FePt temperature excesses the blocking temperature, the exchange bias decreases dramatically. The effect of surface roughness of BFO layers on exchange bias in the present samples was also investigated. In conclusion there has a large exchange bias on BFO/FePt bi-layers due to well epitaxial structure.

Keywords: epitaxial, BFO/FePt, excha nge bias

Several micrometer thick super-hard tetrahedral amorphous carbon (ta-C) films have been deposited by pulsed laser deposition (PLD) using an excimer laser (248 nm wavelength) onto polished tungsten carbide and silicon substrates.

The aim was to investigate the optical properties (e.g. the optical band-gap as well as the refractive and absorption index in the visible and near-infrared wavelength range) of these layers in dependence of the laser fluence on the target. It will be shown that the refractive index of 2 µm thick ta-C films varies between 2.3 and 2.8 at 632 nm wavelength in dependence of the sp³-content. Besides the absorption index is as low as 0.03 at the highest sp³ content of some 80 %.

The partial transparency of these ta-C layers in the visible range results in interference even at a film thickness up to 2 µm.

Furthermore, it will be shown that the ta-C films have low background fluorescence in the wavelength range of 380 - 750 nm, which may be used, as we are going to show, for optical and biotechnological applications.

One possible application is Lab-on-Chip (LOC). Thereby, the ultrasensitive detection of fluorescence markers and of dyes is one challenge in LOC applications. In order to increase the signal-to-noise-ratio, we developed a setup, which uses the specific optical properties of ta-C films produced by PLD. An integrated ta-C film based reflector combines the low background fluorescence, the low reflectivity at the excitation wavelength and the high reflectivity at the emission wavelength.

In this paper, we will show how we can improve the detection of fluorescence photons and with it the resolution of the fluorescence images by using ta-C films.

We will show that ta-C films, which are produced by PLD, have a high potential for optical applications.

20 kinds of amino acids were added to Ni electroplating bath in order to the effect on the characteristics of electroplated nickel films, i.e., surface morphology, film composition, crystal structure, and hardness.

Tantalum nitrides, TaN, were deposited by magnetron sputtering technique with sequential crystalline and amorphous layer stacking to form heterostructurally nanolayer films. The single component TaN layers with amorphous and crystalline phases could be controlled by N₂/(Ar+N₂) inlet gas ratio during fabrication. The amorphous TaN layer was formed under a N₂/(Ar+N₂) ratio over 0.25, while the TaN layer crystalized at a ratio lower than 0.10. Sharp and intact interfaces between amorphous and crystalline layers could be observed through detailed microstructure analysis. Electrochemical tests, including potentiodynamic scanning and A.C.(alternating current) Impedance, were utilized to evaluate the chemical stability of the TaN nanolayer films. The single layer crystalline and amorphous TaN coatings were also investigated for comparison. The amorphous TaN layer exhibited a highest non-negative corrosion potential, E_corr, around 0.3 V, while the nanolayer coating with amorphous/crystalline stacking possessed a lowest corrosion current, I_corr, of 2.0*10^-6 A/cm₂. Furthermore, the impedance of the crystalline TaN single nitride coating was enhanced by the heterostructural nanolayer feature.

Computational studies such as finite element methods (FEM), molecular dynamics or ab initio calculations are integral parts of state of the art materials design. While FEM is commonly used to investigate flow behavior, strain and temperature profiles in various machining processes, this work focuses on utilization of ab initio calculations for an atomistic insight into material transfer phenomena during metal machining.

Material transfer from the workpiece onto the coated tool surface is generally considered as troublesome in machining operations, as the tool and/or work piece surface can severely lack quality over operational time. However, the material adhesion results from a complex interaction of machining conditions, workpiece and coating material. As one crucial parameter we focussed on the tribological contact between nitride coating and work piece material and employed ab initio calculations to estimate the chemical driving force for the formation of transfer material build-up at the coated tool surface.

We thereby investigated the adsorption energies of iron and aluminum with respect to different coating systems (TiN, AlN, TiAlN, TiSiN, CrN, and CrSiN) and were thus able to describe the energetic interplay between workpiece and coating material. The obtained results propose that especially Si containing coatings clearly decrease the adsorption energy for Al, but have less effect on Fe.

The present study introduces a methodology to thoroughly understand tribosystems at the atomic level, which further enables for an efficient coating material screening and selection as an alternative to cost and time consuming experiments.

Recently, high speed dry machining without coolant in the milling application is an important issue in the cutting tool industry to reduce the machining cost and the environmental problems.

One candidate for achieving this goal is deposition of PVD coating layer on the cutting tool which has the rigid low friction property for easy lubrication and high wear resistance in the high speed dry machining conditions.

For that reason, Vanadium Nitride (VN) hard coating has been widely investigated for various cutting tools applications as end mills, drills and various inserts, because of its excellent sliding wear resistance with low friction coefficient (μ=0.4).

Several previous studies have reported that low friction of VN hard coating is come from formation of surface oxide phase, such as V₂O₅, where the suitable heat and pressure generating conditions are satisfied, and self-lubrication by easy sharing of oxide phase.

In this study, VN films were grown on the commercial cemented tungsten carbide substrate via Arc Ion Plating (AIP) method. And the influence of nitrogen partial pressure and negative substrate bias voltage effects for the microstructure and mechanical properties of VN films were investigated. Additionally, the oxidation behavior of the VN coated layer was also evaluated.

Microstructure, phase and chemical bonding analysis of each coating layer are done by Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS), respectively.

And a ball-on-disc type tribometer was used to identify the fiction characteristics and behaviours of various VN films at the dry sliding condition.

From the research results, VN hard coating in this study can be a potential candidate of the lubricious materials for improving the machining performance at high speed with the dry cutting condition.

Multilayer hard coatings are used routinely for metal cutting because they can withstand the extreme conditions that usually prevail. Such coatings need to be hard, have a chemical inertness towards the working piece and they must have an excellent adhesion. In the case of CVD coated cutting tools multilayer coating system is usually used where one or more components is composed of Ti(C,N), often in combinations with Al₂O₃. It is of importance to understand the nucleation and growth of Ti(C,N) on different substrate surfaces. By increased knowledge and control of nucleation and growth of Ti(C,N), properties such as wear resistance and adhesion can be tailored.

In this work growth of MT-CVD Ti(C,N) on (001) sapphire substrates has been studied by means of X-ray diffraction and electron microscopy. The coatings were extremely fine grained and smooth and were found to have a preferred orientation of (211) despite a large lattice mismatch with the (001) oriented substrate. However, a low intensity peak originating from the (111) plane was observed by XRD suggesting that, at an initial stage, the growth of Ti(C,N) was affected by the substrate. At a later stage, the process switched to growth in the <211> direction.

The reason for this two-step transformation is probably kinetically driven where growth in the <211> direction was favored by a fast growth rate and growth in the <111> direction was favored by an initial matching epitaxy to the sapphire substrate. By changing the process parameters to lower the growth rate, the initial epitaxial growth direction of the T(C,N) could be maintained and coatings having a growth along the <111> direction could be grown.

Vanadium carbide coatings onto tool steel AISI H13 and AISI D2 were obtained using thermoreactive deposition/diffusion process (TRD). Four different percentages of ferroalloy were used and Corrosion resistance of vanadium carbide layers was evaluated using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in a solution with 3.0% of NaCl . The microstructure was characterized by X -ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that the coatings thickness increases between 2μm and 10μm with vanadium content. The corrosion resistance increases with increasing the percentage of ferroalloy. Coatings with 20% of ferrovanadium on AISI D2 had the highest corrosion resistance with respect to the layers analyzed. These details are discussed in this research.

Production research for industrial coatings from thermochemical processes plays an important role in materials science. Thermoreactive Diffusion deposition technique (TRD), points to obtain homogeneous coatings, continuous and resilient simple procedures at cost.

The coating was deposited in gray iron pearlitic matrix with randomly distributed lamellar graphite and 3.5% at total carbon. The process was carried out in a salt bath of molten borax at 940 ° C for 2 to 5 hours. Ferro-Vanadium is used as the carbide-forming element and aluminum as the reducing agent.

The coatings obtained were characterized by scanning electron microscopy (SEM), Auger Electron Spectroscopy (AES), and X-ray diffraction (XRD). SEM showed compact, continuous, homogeneous coatings and smooth interface. From XRD was observed with a composition consisting of VC, with preferential orientation in the (222) and (400). From AES was verified the presence of Vanadium at 471,8 eV and carbon in 266.8 eV. It also determined a significant increase in the Vickers hardness of 510 for a casting to 2506 ± 46 Vickers for Vanadium carbide coating. They found values of surface roughness of 694 microns.Finally it was found that the corrosion resistance and adhesion to the substrate increases, when evaluated by the technique of potenciodimnamic polarization and resistance by the Scratch.

The BFO sulayer in the artificial superlattice is under biaxial compressive stress whereas the LNO sublayer is under biaxial tensile stress. The smaller is the thickness of the sublayer, the greater is the crystalline quality and the strain state. The hysteresis loops show a large leakage current at frequencies 0.5 and 1 kHz; the polarization decreases with increasing frequency. An intrinsic remanent polarization of the superlattices was observed at the thickness of a sublayer in the range 1.7 – 8.5 nm at 5 kHz. The rounded shape of the hysteresis loop at frequency ≦ 2 kHz resulted from large dc leakage and extrinsic interface effects.

The thermal spray are a technique of deposit coatings in industrial application for the dimensional recovery surfaces, improve properties corrosives and properties of wear, this technique is easy to apply in different metallic substrates because; the aderencia is done by assembling mechanical by molten particle-propelled by an air stream to speeds of 150 m/s , which is applied after which a pair of wires are melted by an electrical arc. With this technique are deposited coatings from Low Carbon alloys to high engineering alloys as you contain nanocoposites; is important the surface preparation according the NACE 01 for adequate adherence. We studied erosion-corrosion of Nanocomposite coatings (Fe, 25Cr, 5B, 6Mo, 15W, 3Mg, 4C, 12Ni, 2Si) and, stainless steel (Fe, 0.3C, 1Si, 1mn, 13Cr) alloy iron and cobal (Fe, 15CO, 0.8 Mn, 0.2Si), deposited through arc thermal spraying deposited on steel AISI- SAE 4340, each separately and a nanocomposite coating mixing the stainless steel and iron cobalt, respectively. We used the manufacturer's recommended settings in individual coatings and made approximation to the optimal parameters for mixtures, depositing layers of 1mm with a base layer of 95Ni, 5Al. The erosion-corrosion test was conducted in suspension composed of 3.5% NaCl and 10% Si with particle size 50-70 AFS in deionized distilled water and varying the speed and angle of impact at room temperature, we determinated electrochemical parameters from potentiodynamic polarization curves TAFEL in static conditions and under the influence of the jet The mechanism of failure was evaluated through SEM analysis and the surface chemical composition was analyzed by spectroscopy of electrons Auger (SAE).

The transition metal carbides have an unusual combination of physicochemical properties, the among best known are high melting temperatures and hardness, for instance, the vanadium carbide (VC) is a hard transition metal and exhibit some other properties like good corrosion resistance. In the same way, Niobium carbide (NbC) studies have shown that it has a good corrosion resistance at high temperatures. Nevertheless, the studies in production and characterization of ternary carbides of these transition metals (VXNbYCZ) have been very few. Therefore, the aim of this work is to present an experimental study of the structural evolution of VXNbYCZ coatings produced by thermo-reactive diffusion (TRD). The treatments were carried out in a molten mixture constituted of borax, ferro-niobium, ferro-vanadium and aluminum, at 1313 K for 3 hours, using a resistance heating furnace. The crystallographic structure of the coatings was determinated by X-ray diffraction (XRD), the morphology of coatings was observed by cross-sectional optical microscopy and the corrosion resistance was analyzed by potenciodynamic polarization test (Tafel Extrapolation). The XRD analysis shows that the coatings are polycrystalline. The optical microscopy exhibited that the coatings grew in homogeneous form with a regular thickness, and potenciodynamic polarization evidenced that the resistance corrosion enhancement with respect than the bare substrate, because the corrosion current (icorr) is less, and the corrosion potencial (Ecorr) is approximately equal to the reference electrode (SCE).

This paper reports on the improving nickel recovery of electroless Ni-P coating process. At present in electroless nickel coating process the nickel recovery efficiency is only in the order of 25%. Remaining 75% of unrecovered nickel is present in the electrolyte bath as waste. Due to poor nickel recovery from the bath the coating cost of electroless nickel is very high. Hence in spite of having unique advantages of electroless nickel coatings such as improved hardness, wear and corrosion resistance, uniform coating thickness etc., the coating process is not much popular among commercial coating industries. To overcome the above problem an attempt is made in the present study to improve the nickel recovery of electroless coating process. Earlier researchers had tried to recover nickel from the used bath and some of them got success in their attempt by further improving the nickel recovery from 25% - 60%. However no attempts have been made to recover nickel during the coating process. First time in the present study the nickel recovery was improved during the coating process by adding excess amount of reducing agent from 25% to 100% in the bath. In order to find out the influence of reducing agents at different coating intervals, the excess amount of reducing agent was added after 30 minutes, 60 minutes and 90 minutes of start of coating process. Nickel chloride and sodium hypophosphite were used as source of nickel and reducing agent respectively. Coating was carried out on mild steel specimens. Coating was done for two hours and volume of bath was fixed as 200ml. The coating parameter pH was varied at three different ranges as follows: 4-5, 6-7 and 8-9. Anionic surfactant sodium dodecyl sulphate was varied at three different concentrations such as before, at and after critical micelles concentration values and added in the bath. The influence of adding excess amount of reducing agent on nickel recovery efficiency, surface finish, micro hardness, coating thickness, rate of deposition and % of nickel and phosphorous on coated samples were investigated. The result showed that after adding 100% of excess amount of reducing agent at 90 minutes of start of coating the nickel recovery was significantly increased from 25% to 65%. The various coatings parameters used in the electroless bath were optimized using taguchi technique. The complete experimental details, their results and analysis are reported in this paper.

Keywords: electroless plating, nickel recovery efficiency, reducing agent, coating parameters, optimization, surfactant

Newly developed TiAlSiCN coatings with specific structure, in which TiAlCN columnar grains 10-30 nm wide are separated by a SiCN amorphous tissue, demonstrate combination of high hardness in a range of 40-50 GPa, elastic recovery >60%, good impact and wear resistance in different environments, corrosion resistance in alkaline solutions, and high thermal stability up to 1300⁰C [1-4]. Even after annealing at 1500⁰C TiAlSiCN exhibits acceptable hardness of 20 GPa, and crystallite size <50 nm. However practical application of TiAlSiCN is still limited by a relatively low oxidation resistance: complete oxidation at temperatures > 1000⁰C [3]. Addition of optimal amount of Y drastically improves the oxidation behavior of the Ti-Al-N-based coatings and promotes grain refinement resulting in lower residual stresses in the coatings. Hf-alloyed TiN and Ti-Al-N coatings show improved oxidation resistance and high-temperature tribological characteristics. The aim of the present work is to study the structure of Y- and Hf-doped Ti-Al-Si-C-N coatings produced by magnetron sputtering and magnetron sputtering combined with metal ion implantation.

The TiAlSiCN composite target for sputtering was produced by self-propagating high-temperature synthesis. High energy bombardment by Hf⁺ and Yⁿ⁺ ions was implemented at the initial stage of deposition or assisted during the whole process. Accelerating voltage and current of the MEVVA type ion implanter were kept constant at 30 kV and 10 mA, respectively. Doped coatings were also produced using mosaic cathodes composed of TiAlSiCN and Y or Hf segments. The structure of coatings were studied by means of glow discharge optical emission spectroscopy, X-ray diffraction, X-ray photoelectron, Raman and electron energy loss spectroscopy, high-resolution transmission and scanning electron microscopy. Influence of Y and Hf additives on chemical and phase composition, texture, crystallites geometry, morphology, and topography of TiAlSiCN coatings are discussed. Preliminary results of structural investigation of alloyed coatings after air annealing at T> 1000⁰C are also presented.

[1] F.V. Kiryukhantsev-Korneev et al. Russ. J. Non-Ferr. Met. V. 54, №4 (2013) 330–335.

[2] D.V. Shtansky et al. Surf. Coat. Technol. 206 (2012) 4840–4849

[3] D.V. Shtansky et al. Surf. Coat. Technol. 205 (2011) 4640–4648

In this work, we report on the preparation of Ti1-xAlxN thin films by a novel way, namely Reactive Chemical Vapor Deposition (R-CVD). Recently we have grown Ti1-xAlxN films by R-CVD from titanium tetrachloride, hydrogen and c-plane (0001) monocrystalline hexagonal aluminium nitride layers at varied temperature between 800°C and 1200°C. Onemicron-thick monocrystalline AlN layers have been prepared at 1500°C with a gas mixture of NH3 and AlCl3 on c-plane (0001) monocrystalline sapphire substrate1. The Ti1-xAlxN thin films have been analyzed by Field Emission Gun Scanning Electron Microscopy (FEG-SEM), Transmitting Electron Microscope (TEM), and X-ray Diffraction (XRD). Additionally,thermodynamic simulations have been carried out to predict the influence of the major operating parameters.

In this presentation, we focus on the chemical processes between the Ti1-xAlxN solid phase and the chlorine-based gaseous phase. The effect of the process conditions such as temperature, composition of the gas phase, deposition time on the thin films’ properties (composition, thickness) will be discussed regarding both experiments and thermodynamic calculations. As a typical result, 70-nm-thick layer with (111)-oriented cubic Ti1-xAlxN (0.1≤x≤0.45) has been obtained. Work is going on to propose the best conditions for preparing Ti1-xAlxN thin films by reactive CVD.

Nanocrystalline CrZrN coatings with a Cr interlayer were deposited on AISI H13 steel substrate using unbalanced magnetron sputtering system. Although a metallic interlayer was generally used to improve adhesion property by reducing stress gradient between the coating and the substrate, the effect of the interlayer thickness on the adhesion property of the CrZrN coating has not been studied. In this work, the CrZrN coatings with various Cr interlayer thickness from 0 to 600 nm were deposited and the total thickness of the coating was 3 μm. The hardness, crystalline structure, microstructure, surface roughness, and adhesion property of the CrZrN coatings were evaluated by Fischer scope, X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), and scratch tester. The hardness of the CrZrN coatings, ranging from 32-34 GPa, did not show significant dependence on interlayer thickness. The preferred growth orientation of CrZrN coating without interlayer was CrZrN (111). As interlayer thickness increased, the growth orientation changed into CrZrN (220) and at the same time, the rms roughness of CrZrN coating increased from 2 nm with up to 450 nm thick interlayer to 7 nm with 600 nm. The critical load Lc3 showed the maximum value of 32 N at the interlayer thickness of 300 nm. The scratch failure mode changed from the buckling crack and spallation below 450nm to the wedging spallation at 600nm. This result could be attributed to that the shear failures at interlayer became dominant as the thickness of the soft metal interlayer increased.

Acknowledgement

“This research was supported by a grant from the Advanced Technology Center(ATC) Program funded by the Ministry of Trade, Industry& Energy of Korea”

A hollow cathode plasma discharge inside a blind hole has been evaluated concerning its electrical properties and its plasma stability. The governing parameters (i) gas pressure and (ii) exciting voltage were varied and conductivity curves were derived.

The experimental setup was an electrically contacted steel body that was isolated to the ground potential. The working gas Argon was supplied via a ceramic capillary. The dynamic pressure was measured at the end of the blind hole using a MEMS pressure sensor.

First experimental series investigated the relationships between gas flow rate, inner pressure and penetration depth of the capillary. Linear correlations were found (i) between gas flow rate and inner pressure and (ii) between capillary position and inner pressure. Furthermore, the experiments revealed the range of reliable, stable process and measurement conditions that were taken as experimental array for the subsequent investigations.

Oscilloscope measurements revealed the influence of the process input parameters frequency, duty cycle and voltage on the resulting ignition and stability behavior of the plasma. The maximum value of the voltage pulse was found to have the highest influence. This voltage pulse itself can be controlled by the average voltage, the off-time and the frequency.

Based on those results the conductivity curves for different capillary penetration depths, gas flows and voltages were established. The conductivity curves clearly revealed the range of the plasma stability: The lower limit is the transition to the normal glow discharge while the upper limit is the transition to the arc discharge that is detected by the power supply as a voltage drop. Additionally a strong influence of the capillary position not only on the pressure but also on the electrode surface area and hence on the resulting current was found.

Transition metal alloying of Cr_1-xAl_xN based coatings is commonly used to improve their mechanical properties and thermal stability. Recent reports show that Tantalum additions to Ti_1-xAl_xN type coatings positively influence their properties, but only little information is available on the effect of Ta on Cr_1-xAl_xN based coatings. Consequently, we have performed a combined experimental and ab initio based study on the influence of Ta additions (0, 2, 6, 12, and 26 at% on the metal sublattice) on structure and mechanical properties of arc evaporated Cr_1-x-yAl_xTa_yN coatings with Al/(Cr+Al) ratios > 0.61. With increasing Ta-content the droplet number density decreases and coating surface smoothens, which is much more pronounced as with increasing the bias voltage from ­­–40 to –120 V. Simultaneously, the columnar structure observed for Ta-free Cr_0.37Al_0.63N significantly changes into a fine grained structure (crystallite size ~5 nm) with clearly reduced columnar character. Additionally, increasing the Ta content favors the formation of a preferred 200 growth orientation resulting in a reduction of the indentation moduli from ~500 to ~375 GPa, which is in agreement with ab initio calculations. As the hardness of our coatings remains at ~35 GPa with increasing Ta content, this indicates an increase in fracture toughness at still high resistance against plastic deformation.

The challenging problem currently facing the scientific community in this 21^st century is design, fabrication and engineering of novel structural materials, which will have a technological impact on the development of next-generation nuclear reactors to secure current, emerging and future energy needs of the society. Specifically, the choice of structural materials and options for nuclear reactors is very challenging for the reason that these materials experience: (a) extreme conditions of temperature and pressure, (b) high levels of nuclear irradiation, and (c) high mechanical and thermo-mechanical stresses. Tungsten-based materials have been considered for nuclear reactor applications for many years. While pure W exhibits compatible properties, it has low fracture toughness at all temperatures [#] . In addition, it exhibits a high ductile to brittle transition, which depends on the chemical and microstructure. Therefore, alloying W with other metals has been considered to further improving the physical properties and mechanical properties. In this work, alloying W with yttium (Y) has been considered to develop the structural materials for nuclear applications. W-Y (Y<10 wt.%) coatings were deposited by RF sputtering. Characterization of these coatings is performed to derive an understanding of the micro-structure, thickness evolution, specific phase formation and/or transformation, and texturing with respect to deposition conditions. Coatings deposited at 3.4x10^-2 mbar exhibit better structural order with a completely dominant β-phase when compared to the samples deposited at sputtering pressure of 1.4x10^-2 mbar. The deposition rate (Γ) also decreases from 21 to 10 nm with increasing argon pressure from P_Ar=1.9E-2 mbar to 3.4E-2 mbar. Rutherford backscattering (RBS) spectroscopy of W-Y films demonstrated Y inclusion in the lattice [#] in the range of 1-5 wt%. The average grain size decreases with increasing pressure. Calculations were made using the Stopping and Range of ions in Matter (SRIM 2013) simulation package to understand the ion-irradiation damage as a function of time. The results will be presented and discussed.