ICMCTF2015 Session BP: Symposium B Poster Session

In aluminum die casting applications corrosion and wear resistance have significant influence on tool life and product quality. Multilayer coatings based on transition metal nitrides such as CrN and AlN deposited via physical vapor deposition (PVD) have shown great advantage as protective coatings on tools and components subject to high loads in tribological conditions. Al₂O₃ coatings offer high potential to be used as protective coatings on die casting applications due to their high hardness, high chemical inertness and thermal stability. However, the deposition of Al₂O₃ onto steel substrate demands the use of a bond coat such as CrN/AlN in order to improve its adhesion on the substrate. The present work deals with the investigation of CrN/AlN and CrN/AlN/Al₂O₃ coatings deposited at 250 °C using pulsed cathodic arc evaporation on plasma nitrided AISI H11 (1.2343) hot work steel. The chemical composition, morphology and structure were analyzed by means of EPMA (Electron Probe Micro Analysis), SEM (Scanning Electron Microscopy), TEM (Transmission Electron Microscopy) and XRD (X-ray Diffraction), respectively. Mechanical properties were determined by means of nanoindentation. The coating adhesion was studied using the Rockwell (HRC) indentation method and scratch test. The wear and corrosion resistance of the coated substrates were investigated using a rotating immersion test in aluminum melt at 680 °C for two and six hours. The results revealed that a high adhesion of the CrN/AlN and CrN/AlN/Al₂O₃ coatings to the steel substrate was achieved. The CrN/AlN/Al₂O₃ showed a reduced adhesion affinity to the aluminum melt and a high wear resistance. Furthermore, the Al₂O₃ top layer prevented metal physical corrosion between the aluminum melt and the hot work steel substrate. Based on these results the CrN/AlN/Al₂O₃ coating is a promising candidate to be applied on aluminum die casting tools.

CrAlSiN hard coatings with Cr/Al atomic ratio ~1.00 were deposited on WC/Co substrates with different thickness and negative substrate bias by the LAteral Rotating Cathodes Arc (LARC^®) technology. The principal aim of this work is to contribute to the actual knowledge about CrAlSiN coatings, especially in terms of the bias voltage and thickness influence on structure, texture, residual stresses, hardness and adhesion within the relation with coating properties. The X-ray diffraction, nanoindentation and scratch tests were performed for the coating’s analysis.

Al₂O₃ alloyed with Cr is part of coating development for the cutting tool industry. It is commonly synthesized in a vacuum arc discharge from Al-Cr compound cathodes in an oxygen atmosphere. Due to formation of Al-rich oxide islands on the cathode surface, the process stability is highly sensitive to the oxygen pressure. For improved stablity, use of Al_0.70Cr_0.25Si_0.05 cathodes have been reported, suggesting that Si reduces the formation of such islands. In addition, no Si was found in the coating, explained by possible formation of volatile metastable SiO species.[1]

To increase the understanding of the effect of Si in the cathode on plasma generation and thin film deposition, we have characterized the cathode surface, the plasma chemistry, and the resulting thin film for Al_0.7Cr_(0.3-x)Si_x (x=0 and 0.05) cathodes used at different oxygen and argon pressures in a dc vacuum arc system. Vacuum plasma analysis shows a plasma ion composition consistent with the cathode composition for the Al_0.70Cr_0.25Si_0.05 cathode, with average ion energies of 30, 58, and 32 eV for Al, Cr, and Si, respectively. Introducing O₂ to a pressure of 3x10^-2 Torr, the energies are reduced to 16, 20, and 17 eV, and the relative Si ion content in the plasma is slightly reduced from 5 % to about 3 %. Furthermore, analysis of neutrals in the plasma shows a significant amount of Si and SiO species, supporting previous suggestions in the literature. Also in Ar there is a reduction of Si ions, from 5 to 2%. The here presented plasma characterization will be correlated to results from XRD and EDX analysis of the cathode surface as well as of the film.

[1] Paulitsch, J., et al., Vacuum, 2014. 100: p. 29-32

This study employed artificial intelligence methods such as the Taguchi Method to determine the optimal parameters for CoMoCrSi alloy coatings using a thermal spray technique. We determined the optimal parameters to produce coatings and investigated CoMoCrSi alloy coatings by observing and analyzing changes in the microstructure and properties. These artificial intelligence methods comprised two stages. In the first stage, orthogonal arrays (OA) were used to distribute test parameters, and the Taguchi Method was used to optimize the parameters. In the second stage, investigate the microstructure and properties of the specimen of CoMoCrSi alloy variations of the coating, an attempt is made to produce high quality coatings by optimizing the thermal spraying process parameters using Taguchi techniques. The microstructure of the CoMoCrSi alloy coating on Ti-6Al-4V substrate, which exhibited did not undergo any change in phase. In addition, the experiments are conducted using ASTM specimens to produce coatings which have high cohesive strengths that these data will serve as a practical reference for aviation power plant systems in the future.

There is an increasing need of light material in automotive, aerospace, biomedical application and electronic industries. Due to the low density and low price, magnesium and magnesium alloys have been widely used as structural materials in these industries. However, the application of magnesium and its alloys is limited because of their low corrosion and wear resistance. Coating the magnesium alloy surface with transition metal nitrides based on Ti, Cr and V using magnetron sputter is an effective method to overcome these problems. [1, 2]

In this study, TiN, TiVN and TiN/VN multilayers were coated on AZ91D magnesium alloys using RF magnetron sputter technique and the influence of these coatings on the mechanical properties of Mg alloys was investigated. The composition, surface morphology and corrosion resistance of the coated magnesium alloy were analyzed by x-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and electrochemical measurements, respectively. TiN and TiVN hard coatings improved the corrosion resistance of the AZ91D magnesium alloy in 3.5 wt% NaCl solution in the same way. However, TiN/VN multilayer coatings deposited at the same sputtering power showed higher corrosion resistance and low surface roughness in comparison with the TiN and TiVN coated films. XPS results showed that at the early stages, the coating was mainly consisted of TiN, TiON and TiN_x; however as the coating thickness increases it is dominated by TiN. Forming two bilayers of TiN and VN with the same thickness improved the roughness of the film surface and increased the corrosion resistance of the coated films. TiN/VN codeposition films deposited at the same parameters showed low corrosion resistance comparison with TiN and TiN/VN multilayer film deposited. These results suggest that magnetron sputtered TiN/VN multilayer film coatings enhances the mechanical properties of AZ91D alloys. This study is supported in part by The Scientific and Technological Research Council of Turkey.

1. Seal, S., Transition metal nitride functional coatings. Jom-Journal of the Minerals Metals & Materials Society, 2001. 53(9): p. 51-54.

2. Altun, H. and S. Sen, The effect of DC magnetron sputtering AlN coatings on the corrosion behaviour of magnesium alloys. Surface & Coatings Technology, 2005. 197(2-3): p. 193-200.

Aluminium based oxides are prominent representatives of functional coatings for protective application. Depending on the crystallographic constitution and growth conditions, a broad spectrum covering chemical, mechanical, and thermal performance can be attained. Particularly, the thermodynamically stable corundum phase attracts attention and is of great interest for industrial application. Typically synthesised by CVD, an increasing demand for low temperature PVD deposition is given. However, the growth of single-phased α-Al₂O₃ coatings at deposition temperatures lower than 600 °C turns out to be challenging. On this account the alloying of Cr to form a solid solution (Al,Cr)₂O₃, or the utilisation of a Cr₂O₃ and Cr-rich (Cr,Al)₂O₃ as seed layer are promising approaches, which, however, are not entirely satisfactorily for high Al-concentrations.

In this work we extend the concept of a bilayer architecture to an alternating multilayer arrangement. The (Cr,Al)₂O₃ seed layer processed from powder metallurgically produced Cr_0.75Al_0.25 targets is followed by either (Al,Cr)₂O₃ or (Al,Cr,Fe)₂O₃ layers for which we used Al_0.7Cr_0.3 and Al_0.675Cr_0.275Fe_0.05 targets, respectively. Variations in the layer periodicity is realised by the arrangement of mounted cathode materials as well as slight variations in cathode powering.

X-ray diffraction analyses suggest the growth of multi-phased films consisting of a hexagonal and cubic phase. However, in contrast to the Al-rich (Al,Cr)₂O₃ coating—representing our benchmark system—the amount of cubic phase fractions can be significantly reduced. Thereby, an alternating arrangement of Cr_0.75Al_0.25 and Al_0.7Cr_0.3 (or Al_0.675Cr_0.275Fe_0.05)₂O₃, hence smallest bilayer period, shows the most pronounced XRD peaks with only marginal cubic reflections. Supplementary transmission electron microscopy investigations confirm the XRD results and reveal a predominant and well-defined hexagonal morphology. Predominant metastable cubic phase fractions could only be determined at the interface to the substrate, hence where initial film growth occurs.

ZnO is a hexagonal n-type semiconductor with a band gap energy of 3.2eV; Al-doped ZnO (AZO) would increase the electron concentration via the substitution of Zn²⁺ by Al³⁺ (~1.6wt% Al of the AZO target). In this work, carbon-doped AZO thin films have been successfully deposited on glass substrates by reactive pulse-DC magnetron sputtering, using AZO ceramic target under flowrate of C₂H₂ (0, 3, and 5 sccm). AZO is one of the transparent conductive oxide (TCO) thin film and much stable in hydrogen plasma than ITO, low cost, and nontoxic. C-doped AZO would further increase the electron concentration through the dissolved carbon atoms, which creating more anion vacancies by the formation of CO bonding. Both substitutional Al atoms and interstitial C atoms could effectively increase the negative charge carrier in the C-doped AZO. Higher concentration of the mobile electrons would reduce the electronic resistivity, but still lower than the critical concentration for the visible light (400-800nm), n_c ~10²¹cm^-3 according to the relation:

n_c=ω²ε₀ m_e /e²≧ n_e (~10²⁰cm^-3) thus facilitating the transmission of visible light through the C-doped AZO.

There are two major peaks of (002) and (103) observed on the XRD pattern with a trend of decreasing intensities as the flowrate of C₂H₂ increases, accounting for the gradual build-up of amorphous carbon films on the surface of AZO. Raman spectra clearly indicate the bonds of C-O, Zn-O, and C-Zn appearing at 275, 510, and 575 cm^-1, respectively; no signals of disordered and/or graphitic carbon respectively on ~1300 and ~1500 cm^-1 were detected. Intrinsic carbon is always detected in the high vacuum system, which appears at 284.1eV. However, a nearby extra peak of 285.1eV could be resolved when 5 sccm C₂H₂ was admitted to the reactor. This result is apparently due to the incorporation of the interstitially dissolved carbon atoms to the AZO. Optoelectronic performances, as the results of characterization, were obtained and derived from the evaluation are: the optical transparency (400-800nm): 87%; carrier mobility and concentration: 19.5 cm²/V-s and 6×10²⁰ cm^-3; and resistivity: 5.58×10^-4 ohm-cm . It is worth noting that better optoelectronic properties appear at the condition when the XRD intensity of (103) > (002); both intensities tend to decrease as the C₂H₂ flowrate increases.

Cubic molybdenum nitride coatings exhibit high hardness and thermal stability and thus have a high potential to be used as wear-protection for various high-demanding applications. However, the formation of volatile molybdenum oxides requires an improvement of their oxidation resistance. Here, alloying of MoNx thin films with aluminium is an ideal tool, since Al forms stable dense oxides preventing both, further oxygen inward and molybdenum outward diffusion.

Although face centred cubic fcc-Mo₂N (nitrogen deficient NaCl structure) and hexagonal close packed hcp-AlN (wurtzite ZnS structure) are thermodynamically not miscible, using non-equilibrium physical vapour deposition (PVD) techniques allows to synthesise their metastable solid solutions. We show, that by PVD single-phase fcc-Mo–Al–N coatings can be developed for Al-contents [x=Al/(Mo+Al)] up to 0.34, where also the hardness reached its maximum with 37.4 GPa. Furthermore, these coatings exhibit also a relatively high resistance against plastic deformation with H³/E*² = 0.24 GPa. According to X-ray diffraction analysis and ab initio calculations these single-phase fcc-Mo–Al–N coatings crystallize along the quasi-binary Mo₂N–AlN tie line.

L1₀ FePt thin films have attracted considerable attention for application of high-density recording media due to its high magnetocrystalline anisotropy. L1₀ ordering accompanied with lattice distortion can induce extrinsic compressive stress in FePt thin films. In the previous study, we reported that densification reaction could induce a tensile stress, which facilitates the nucleation of L1₀ ordering for the films with small initial stress (σ_i). The purpose of this paper is to clarify the microstructure and internal stress evolution during the densification in the FePt films with different σ_i. A considerable variation in e_r was observed before L1₀ ordering for the films with different σ_i (Fig. 1). As annealing temperature (T_a) was increased, e_r increased dramatically to a maximum (e_max) toward the tensile direction, then subsequently relieved to a local minimum, after that e_r gradually increased again with T_a to 700 ^oC. The accumulation of tensile stress results from the densification reactions during annealing, evidenced by microstructural observation (not shown here). Fig. 2 shows the TEM images of the samples with exhibiting e_max at different σ_i. The SADs connect the drop of e_r to the nucleation of L1₀ phase for the FePt films with different σ_i, confirmed by the appearance of diffraction (110) spots. We also found a grain growth from about 5 nm for the as-deposited state to ~50 nm after nucleation for the films with σ_i < –0.5 GPa (fig. 2a and 2b). On the contrary, for the films with σ_i = –1.01 GPa, the grain size after nucleation is about 5 nm, similar to that of as-deposited films (Fig. 2d). This indicates the fact that compressive σ_i suppresses growth of the disordered grains, which leads to a smaller densification stress and further sluggish L1₀ ordering transformation.

The CrZrN coatings have been paid much attention to cutting tool’s coating due to their high hardness, low surface roughness and excellent tribological property. The adhesion strength between substrate and coating is essential property to protect cutting tool, and could be improved by addition of interlayer. The Cr-N coatings were reported to show various crystalline phases and properties with various nitrogen contents in coatings. Therefore, the Cr-N coatings of various properties can be controlled with various nitrogen contents.

In this study, the CrZrN coatings with the Cr-N interlayer with various N₂ partial pressures in the range from 1.1×10^-1 to 2.3×10^-1 Pa were synthesized using the unbalanced magnetron sputtering system on WC-6wt.% Co disc type substrate. The crystalline phase, microhardness and elastic modulus, microstructure, and adhesion properties of the CrZrN/Cr-N coatings were evaluated by x-ray diffractometer, Fischer scope, field-emission scanning electron microscopy, scratch tester and optical microscopy, respectively.

The crystalline phase of Cr-N interlayers varied from single-phase Cr₂N to CrN+Cr₂N, and then single-phase CrN with increasing N₂ partial pressure. The microhardness and elastic modulus of all the coatings gradually decreased from 28.5 to 23.3 GPa and 357.5 to 340.2 GPa, respectively. The critical load (Lc3) of the CrZrN/Cr₂N and CrZrN/(CrN+Cr₂N) coatings ranging from 26.8 to 28.7 N showed similar values. However, the critical load (Lc3) of the CrZrN/CrN coating significantly increased to 46.1 N. It could be attributed to the interlayer’s hardness to elastic modulus ratio (H/E) between the WC and CrZrN coating. The H/E ratio that is related to elastic strain to failure influences to adhesion strength. In this case, the H/E ratio of the CrN interlayer (0.068) showed a suitable median value between the WC (H/E=0.045) and CrZrN coating (H/E=0.090) comparing with Cr₂N (H/E=0.079) and CrN+Cr₂N (H/E=0.077). The results showed that the single-phase CrN interlayer reduced stress gradient effectively. Detailed experimental results will be presented.

The development of plasma sources for various types of plasma processing, such as, etching and thin film deposition show that one important parameter for effective plasma processing is high plasma density [1]. One type of high density plasma source is Microwave sheath-Voltage combination Plasma (MVP) [2-6]. MVP allows a tremendous increase in productivity for the deposition of Diamond-like carbon (DLC) coatings [7-9] since hard coatings of Si-DLC can be deposited with more than 100 micrometer/hr. A design tool for optimizing the reactor is highly welcomed by the industry. The MVP device requires the combination of well known microwave surface wave plasma with a resolution of the superimposed DC-plasma sheath.

We present a better design of MVP source, in which the input microwave power couples with plasma very efficiently through an extended antenna and over-dense plasma is generated for low input microwave powers. This design would replace the challenging of building ever bigger coatings tools by using eco-friendly and low budget fast one-to-one automated deposition systems. Also we report on first qualitative agreements of the plasma modeling using the commercial COMSOL multi-physics plasma module. The simulation results are agreed with experimental results. The results suggest that this MVP device can be used for ultra-high-speed DLC coating.

Acknowledgement

This work was supported partly by DAIKO Foundation RESEARCH FELLOWSHIP PROGRAM in FY2014 and a “Grant for Advanced Industrial Technology Development (No. 11B06004d)” in 2011 from the New Energy and Industrial Technology Development Organization (NEDO) of Japan.

References

[1] M. A. Lieberman and A. J. Litchenberg, Principles of Plasma Discharges and Materials Processing, Wiley, New York, 1994.

[2] H. Kousaka, J. Q. Xu and N. Umehara, Jpn. J. Appl. Phys.44 (2005) L1054.

[3] H. Kousaka, H. Iida and N. Umehara, J. Vac. Soc. Jpn. 49 (2006) 183 [in Japanese].

[4] H. Kousaka and N. Umehara, Vacuum80 (2006) 806.

[5] H. Kousaka, J. Q. Xu and N. Umehara, Vacuum80 (2006) 1154.

[6] H. Kousaka and N. Umehara, Trans. Materials Research Soc. Jpn31 (2006) 487.

[7] H．Kousaka, T. Okamoto, N. Umehara, IEEE Trans. Plasma Sci.41 (2013) 1830.

[8] X. Deng, H. Kousaka, T. Tokorayama and N. Umehara, Surf. Coat. Technol. 238 (2014) 80.

[9] X. Deng, H. Kousaka, T. Tokorayama and N. Umehara, Tribology Online8 (2013) 257.

Nowadays, magnetron sputtering is a commonly used method for the deposition of thin films with industrial applications. Experimental observations reveal that deposition parameters, such as the substrate's nature, growth rate, deposited energy, interfacial effects [1], strongly influence the final material properties.

In this framework, we performed a multi-scale modelling of the growth of thin Molybdenum film sputtered onto a silicon substrate, based on a Monte Carlo algorithm. This system (MoSi) is widely used as a back contact for CIGS-based (Copper-Indium-(Gallium)-Diselenide/Disulfide) solar cells or those based on Silicon. Thus, the multi-scale strategy used helps to shed light on the complex links between the crystalline nucleation of the metal layer and the deposition process in real experimental conditions.

This contribution is focused on the first step of a kinetic Monte Carlo (kMC) code, i.e. a comprehensive ab initio study of the elementary mechanisms which occur during the first stages of the growth. We will first consider molybdenum adsorption and diffusion on Si (100) surface as well as on Mo (110) surface. The most reactive surface sites will then be found. They consist in strong binding sites such as interstitial sites of the first silicon layer. The influence of a second Mo atom on the possible diffusion pathways of the deposited atoms on the two surfaces will be also investigated. The high diffusion barriers found on the silicon surface confirm the low mobility of Mo atoms. The incorporation into the Si subsurface will also be discussed. Results show that, under experimental deposition conditions, Mo migration in the bulk is thermodynamically favorable. We will conclude with some preliminary kMC results.

[1] A. Fillon, G. Abadias, A. Michel, C. Jaouen, P. Villechaise, Phys. Rev. Lett,104 (2010), 096101

It is well known that the Zn-Mg coating has higher corrosion resistance compared with the pure Zn coating due to the formation of the simonkolleite phase on the surface of the Zn-Mg coating. Therefore the Zn-Mg coating has been studied extensively for the corrosive protection coating in the automobile applications. To obtain Zn-Mg coating, an induction evaporation process is considered to be one of the strong candidates due to its high deposition rate and low energy consumption.

In this study, the effect of the design of the induction coil and size of droplet on the efficiency of high-frequency induction heating was investigated. This investigation first utilized electromagnetic and thermal simulation using MagNet, ThermNet software to predict the electric field and temperature distribution during the induction heating process. The finite element method was then adopted to determine the best combination of process parameters with various induction coils. The most efficient coils were produced for the application of the atmospheric evaporation test. The results of the atmospheric test were measured against the simulation results to draw the best induction heating condition.

The simulation results indicated that the heat value of droplet and induction coil by high-frequency induction heating increased linearly with decreasing the coil gap of turns from 7 mm to 3 mm. When the coil and the droplet were similar size, the heating efficiency was the highest at all turns of coil. For the highest heating efficiency of droplet with reducing heat value of induction coil, the coil with medium gap were produced. At the atmospheric evaporation test, the heating efficiency increased by 50% or more with increasing the size of droplet. However, when the droplet was larger than induction coil, the efficiency decreased contrastively. The results for the atmospheric evaporation test corresponded well to those of the simulation results and the conditions of high-frequency induction heating for the highest efficiency could be utilized for the synthesis of Zn-Mg coating in high vacuum environment.

Acknowledgement

This work was financially supported by the Smart Coating Steel Development Center operating for the execution of WPM (World Premier Materials) Program funded by the Ministry of Trade, Industry and Energy, Republic of Korea.

In recent years, the application of AlCrN-type coatings in processes which involve attrition, chipping and/or cracking due to the impacts, such as the industrial metal forming has increased [1]. The cutting edge of coated tools may exceed 1000°C, therefore the oxidation resistance is a very important issue [2]. The oxidation resistance and high temperature mechanical properties of AlCrN are improved comparing with other ternary nitride such as AlTiN [3]. On the other hand, to increase the tribological properties of AlCrN, nanolayered coatings containing vanadium are an interesting solution [4]. Indeed, when vanadium-based coatings are submitted to high loads and high temperature conditions, the formation of so-called Magnéli-phases V_nO_2n-1 is induced and the latter allow the reduction of friction coefficient (µ<0.1) at high temperature [4].

In this study, AlCrN/VN nanolayered coatings were prepared by vacuum cathodic arc deposition (CAD). The mechanical tests including nano-indentation and nano-scratching tests were performed and the results are discussed as a function of the bilayer period and the deposition temperature. Ball-on-disc tests were performed at RT and 700°C. The oxides evolution during dry sliding was studied by XRD. Finally, the film characterizations were completed by SEM observation correlating the different phenomena at both temperature regimes.

References

[1] G.S. Fox-Rabinovich et al., Surf. Coat. Technol. 200 (2006) 5738.

[2] H.O. Gekonde et al., Surf. Coat. Technol. 149 (2002) 151.

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

[ 4] K. Bobzin et al. Surf. Coating Technol. 205 (2011) 2887.

CVD α-Al₂O₃ is one of the most suitable outermost coating materials to apply the cutting tool application which is based on cemented tungsten carbide system, and recent researches and cutting tool manufacturer’s products are focused on the properties control of α-Al₂O₃ such as texture and microstructure. Because the upper layer properties of the complex coating layers are significantly affected by lower layers, understanding of underneath layer so-called bonding layer is essential for the α-Al₂O₃ layer deposition.

This study is focused on the CO gas added TiCNO bonding layer which is well known underneath layer of α-Al₂O₃. From the previous XRD, SIMS and microstructure results, it was confirmed that the CO gas changes the lattice parameter, composition and microstructure of CH₄ based high temperature TiCNO significantly but could not revealed the detailed texture conditions of the CO gas added TiCNO grains [1, 2]. So, to identify the relationship between the lower moderate temperature TiCN and the CO gas added TiCNO grains, very careful EBSD analysis was done for the CO gas added TiCNO bonding layer which direction is normal to the coating substrate. 6 vol% CO gas addition made lenticular type TiCNO grains and most of the grains were divided by two along the longitudinal direction. Grain misorientation angle of two separated grains were ~ 50 degree and it is assumed that most of the grains have same CSL grain boundary. TEM analysis for cross section of the randomly selected grain showed {111} termination and boundary plane was {113}. As revealed at previous XRD data, TEM analysis also confirmed the lattice parameter increment of 6 vol% CO gas added TiCNO which compares to lower layer moderate temperature TiCN, and TEM EDS showed that oxygen from CO was homogeneously distributed in the grain. At the condition of 24 vol% CO gas addition in the TiCNO, CSL grain boundary was collapsed and more homogeneous texture was obtained.

[1] S. Na, J. Kim et al., 40^th ICMCTF. BP26.

[2] S. Na, E. Lee et al., 40^th ICMCTF. BP27.

So, physical and chemical machining for diamond is difficult to obtain any shape diamond because it has high hardness and chemical inertness. On the other hand, nucleation density of during diamond synthesis using CVD method on the silicon oxide substrate is lower than that of on the pre-treated silicon substrate with diamond powders. Therefore, Silicon oxide can be used as a mask for selective growth of diamond.

Investigation was examined on the preparation of three-dimensional structure CVD diamond by control of the nucleation site using the silicon oxide film as a mask.

Polycrystalline diamond films were synthesized on silicon substrates using microwave plasma CVD apparatus. Substrates were scratched with diamond powders and then cleaned ultrasonically in acetone solution. Reaction gas was used mixture of CO (20 SCCM) and H₂(100 SCCM). Pressure was 5.4kPa and microwave power was 400W. Reaction time was 5h. Silicon oxide was deposited on diamond substrates by vacuum evaporation. After diamond growth, Silicon oxide was deposited narrow area again and then diamond growth was performed for 3h in the same condition. The surface and cross-sectional morphologies of deposits were observed by SEM. Qualities of the deposits were estimated by Raman spectroscopy.

As a result of the SEM observation, deposits were not observed on the silicon oxide masking area. Borderline of deposits and silicon oxide film was observed clearly. And, deposits on non-masking area of diamond substrate is thicker than that of on the silicon oxide masking area of diamond substrate.

Peak of diamond at 1333cm⁻¹ was observed in Raman spectra of diamond substrate and non-masking area.

The investigation proved the feasibility of preparation of three-dimensional structure CVD diamond by control of the nucleation site by using the silicon oxide film.

Carbon nitride has fascinate properties such as high hardness and high current density of field emission and so on. In addition, if c-C₃N₄ or β-C₃N₄ structure can be synthesized, it is possible to obtain high hardness exceeding that of diamond. Authors tried to obtain crystal carbon nitride, crystalline deposits were obtained from a CH₄-N₂ reaction gas system using microwave plasma CVD. However, the deposits was included Si because substrate temperature was too high such as 1473K. On the other hand, low substrate temperature, improvement of the film quality and higher growth rate can be obtained by using of pulsed plasma CVD. Investigation was carried out on the effect of pulse frequency of microwave plasma on carbon nitride synthesis.

Carbon nitride was synthesized using improved microwave plasma CVD apparatus. This apparatus equipped water-cooled substrate holder and can be change microwave radiation mode to continuous or pulse. Si was used as the substrate. The mixture of CH₄-N₂ gas was used as a reaction gas. CH₄ flow rate was fixed to 2 SCCM, and N₂ flow rate was fixed to 200 SCCM. Synthesis pressure was fixed to 4.0 kPa, and microwave power was fixed to 400 W. Reaction time was fixed to 7h. Pulse frequency was varied from 30 to 3000Hz, keeping a constant duty cycle of 20%. Surfaces of the deposits were observed using SEM. The deposits were estimated by Raman spectroscopy, AES, and XPS. To estimate of plasma state, the emission species of plasma were measured by OES.

As a result of SEM observation, crystalline deposits similar to the rods of hexagonal were observed for 300Hz of microwave frequency. The deposits similar to the ball were observed for CW, 30Hz and 3000Hz. From raman spectra, only the peak of silicon is observed at 300Hz of microwave frequency. On the other hand, DLC peak was observed at CW, 30Hz and 3000Hz. From XPS measurement, SiC, C-N, C=N and Si₃N₄ bond was observed in all sample. From OES spectra, the all spectrum was dominated by emission of CN radical. In addition, peak height of 336 nm related to NH and N₂ is increased with higher of pulse frequency.

Currently are known many technologies dealing with deposition of thin layers on any kind of basic material and helping to solve the problems of short-term life of tools [1,2]. Thin, hard and wear resistant PVD coatings have the greatest impact on the properties of cutting tools, which include for example lifetime and durability of the cutting tool, the cutting performance, etc. The structure and properties of thin films are especially given by character and technological parameters of the deposition process, in particular the pressure of the working gas, the temperature of the substrate and the size of the bias voltage and the deposition time [3,4]. Among the properties of the coating, which can be influenced by changing the deposition parameters, include the thickness of coatings, their structure, surface morphology, nanohardness, wear resistance, adhesion to the base material and the presence of internal stresses as well [5]

The contribution deals with analysis of AlTiN monocoating layers deposited onto AISI M35 high speed steel surfaces at different values of substrate biases (concretely: 20 V, 60 V, 100 V, 140 V, 180 V) and an influence of laser treatment of substrates before deposition process and deposited coatings as well. LAteral Rotating Cathodes (LARC^®) process was chosen for evaporation of individual AlTiN layers. The influence of substrate bias and laser treatment on AlTiN layers morphology, presence of residual stresses not only inside the layers, but also in substrates and their adhesion behavior between layers and base material will be studied. Scanning electron microscopy fitted with EDX spectroscopy will be used for evaluation of microstructure and surface morphology of coatings. XRD analysis will be employed for detection of phases present in deposited AlTiN coatings and residual stresses measurements as well. Indentation testing, nanohardness measurements, scratch and wear tests will be performed to characterize the mechanical properties of this type of coatings. The aim of this contribution is an assessment of aforementioned AlTiN layers properties on different values of substrate biases and influence of laser treatment on some coatings properties.

References

[1] Richter, A.: Recipe for Enhancement. In: Cutting Tools Engineering, October 2005, Vol. 57, No. 10.

[2] ANTONOV, m., HUSSAINOVA, I., SERGEJEV, F., KULU, P., GREGOR, A.: assessment of gradient and nanogradient PVD coatings behaviour under erosive, abrasive and impact wear conditions. In Wear, Vol. 267, Issue 5 – 8, p. 898 – 906. ISSN: 0043-1648.

[3] CHEN, J. K., CHANG, C. L., SHIEH, Y. N., TSAI, K. J., TSAI, B. H.: Structures and properties of (TiAlSi)N films. In Procedia Engineering, Vol. 36, p. 335 – 340. ISSN: ISSN: 1877-7058.

[4] MO, J. L., ZHU, M. H.: Tribological oxidation behaviour of PVD hard coatings. In Tribology International, Vol. 42, Issue 11 – 12, p. 1758 – 1764. ISSN: 0301-679X.

[5] BIROL, y., YUKSEL, b.: Performance of gas nitrided and AlTiN coated AISI H13 hot work tool steel in aluminium extrusion. In Surface and Coatings Technology, Vol. 207, 461 – 466. ISSN: 0257-8972.

Active Screen technique, as an additional cathode, is an advanced technology used for metal surface plasma nitrating with apparent advantages over conventional one. Side effects such as arcing or other way of plasma instability could be considerably reduced with the use of the active screen technique and thus dealing to an improved surface quality. Because of the absence of information concerning the active screen technique used for DLC growth, specially on different kinds of steels a new and deeper studies about the process will be considered.[1]

Active screen coupled to PECVD system allows obtaining DLC films with lower pressure, lower temperature and low power energy consumption, achieving an inferior production costs with higher adhesion and better quality films in terms of hardness, density and finishing [2]. Also, the homogeneity of the coating in large area is improved [3].

In this work cylindrical actives screens are home manufactured with the same diameter and different mesh sizes. The temperature variation on ss 420 substrate as a function of the time in argon plasma discharge, gas pressure inside of the chamber and screen mesh sizes were carefully measured.

Keeping constant the bias and gas flow, a very interesting results show that the temperature rise faster for higher screen mesh even at very low argon pressure in the plasma discharge and the threshold mesh size and lower pressure value was found. Also a strong dependence of the final temperature with the gas pressure reveal the possibilities of obtaining a better conditions for DLC growth than in the conventional PECVD system. In order to show a great performance of this new system a very good DLC films were obtained with good mechanical, trybological and chemical properties.

References

[1] C.X. Li, J. Georges, X.Y. Li, Surf. Eng. 18 (2002) 453–458.

[2] C.X. Li, T. Bell, H. Dong, Surf. Eng. 18 (2002) 174–181.

[3] S. Corujeira Gallo, H. Dong, Vacuum 84 (2009) 321–325.

Ti_1-xAl_xN is a well-established protective coating system, which is used for various industrial applications due to its excellent mechanical and thermal properties. Especially, the thermal stability and age-hardening effect in the high temperature range 700 – 1000 °C are key-factors for its outstanding performance and versatility. Recent investigations suggest that the grain size has a major influence on the decomposition process and the attainable hardness increase of Ti_1-xAl_xN. Nevertheless, a detailed study on grain size induced effects of spinodal decomposition of Ti Al N is still missing.

Therefore, we have deposited differently structured Ti_1-xAl_xN coatings by reactive magnetron sputtering using powder metallurgical produced Ti_0.50Al_0.50 targets. Through a variation of the deposition conditions - temperature, base pressure, bias voltage, and target power - we are able to deposit Ti_1-xAl_xN coatings with different grain sizes, reaching from a very fine grained/amorphous-like structure up to a crystallite size of more than 150 nm. The morphology and structure were investigated using X-ray diffraction, electron microscopy (scanning and transmission), as well as atom probe tomography. Coatings having the largest grains exhibit hardness values in the range of 21 GPa compared to 32 GPa for the finer-grained coatings. These coatings are vacuum annealed at T_a = 700, 800, and 900 °C for t_a = 1, 10, 100, and 1000 min. Increased diffusion pathways in the large grain-sized coatings lead to a retarded decomposition process. These coatings exhibit a hardness increase of about 8 GPa whereas the fine-grained counterparts only exhibit an increase in hardness by 3 GPa due to spinodal decomposition.

Based on our results we can conclude that the grain size has a pronounced effect on the decomposition kinetics of Ti_1-xAl_xN coatings as well as on the obtained hardness increase due to age hardening effects.

During Al die casting, it is important to prevent the soldering that frequently occurs between the Al alloy and the steel dies and core pins. The overall objective of this study is to develop coatings that are non-wetting with liquid Al with the long-term objective of circumventing the need to use liquid-based organic lubricants prior to each shot. In this research, AlCrN coatings have been deposited on H13 tool steel by modulated pulsed power magnetron sputtering (MPPMS) using two methods: co-sputtering or compound sputtering. The structural, mechanical, tribological and adhesion properties of these coatings will be compared and related to the sputtering parameters, the Al/Cr ratio in the coatings and their overall structure/architecture.

Ti_(1-x)Al_xN hard coatings exhibit beneficial thermal and mechanical properties essential for protective coatings in milling, cutting, or drilling applications. However, ever-growing interests to even higher process temperatures result in the need of further improvement. Therefore, powder metallurgical prepared Ti_0.475Al_0.475Zr_0.05 and Ti_0.375Al_0.575Zr_0.05 targets were cathodic arc evaporated to synthesize Ti_0.49Al_0.44Zr_0.07N and Ti_0.39Al_0.54Zr_0.07N coatings, respectively. The applied bias potential was varied between –40 V and –120 V. XRD analysis indicate, that independent of the bias voltage used, all Ti_0.49Al_0.44Zr_0.07N coatings exhibit a single phase cubic (c) structure, whereas all Al-rich Ti_0.39Al_0.54Zr_0.07N films are composed of a mixed cubic/wurtzite (w) structure. By increasing the bias potential from –40 V to –120 V a significant increase of the cubic phase fraction can be obtained.

Our Ti_0.49Al_0.44Zr_0.07N coatings deposited using low (–40 V) and high (–120 V) bias potentials demonstrate no significant hardness maxima upon annealing in vacuum. Coatings deposited using –80 V bias potential exhibit after vacuum annealing at T_a = 800 °C a slight increase in hardness (from ~35 to ~37 GPa), which can be assigned to age-hardening effects. Contrary to these observations, all Al-rich mixed c/w-structured Ti_0.39Al_0.54Zr_0.07N coatings exhibit enhanced hardness values with increasing T_a. Oxidation treatments at 850 °C for 20 h in ambient air show best performance for the single phased c-Ti_0.49Al_0.44Zr_0.07N coatings deposited at –40 V bias. With increasing bias voltage their oxidation resistance decreases as thereby the defect density increases providing easier pathways for diffusion.

Nanostructured thin films of Nb_xSi_yN_z were grown on stainless steel AISI304 by using unbalanced magnetron (UBM) sputtering. The corrosion resistance was studied by electrochemical impedance spectroscopy and potentiodynamic polarization using a 3 wt.% NaCl saline solution. The chemical composition was identified by X-ray photoelectron spectroscopy, the microstructure was analyzed by X-ray diffraction, and the hardness was measure by nanoindentation. The transition from a crystalline to an amorphous phase was observed for Si contents > 5at.% Si, and the presence of Si₃N₄ and NbN was confirmed by the chemical analysis in all the thin films deposited. The hardness was improved from 18 GPa to 29 GPa for low Si concentrations. The analysis of the corrosion mechanism revealed that the thin films with the highest Si content have low corrosion current density, low porosity index, and high degree of passivation.

Hydrogenated amorphous silicon carbide (a-SiC:H) have several features that make it desirable for tribological applications, as high hardness, low friction coefficient, high corrosion resistance and high temperature resistance. These properties qualify it for use in strategic areas as aerospace, pharmaceutical, biomedical, microelectronics and many others [1-2]. Hydrogenated amorphous silicon carbide (a-SiC:H) films can be obtained by using PECVD at low temperature (< 700 C) [3,4].

This paper presents a study of deposition parameters and results of tribological and mechanical properties of a-SiC:H films deposited on titanium alloy (Ti-6Al-4V). The aim was to obtain films with high adhesion and high tribological performance. The film was deposited using Plasma Enhanced Chemical Vapor Deposition (PECVD) and organosilanes hexamethyldisiloxane (HMDSO), [Si-(CH₃)₃]₂O and tetramethylsilane (TMS) Si-(CH₃)₄ as silicon, carbon and hydrogen precursors. The deposition temperature was varied from 400 to 600 °C and pressure from 0.5 Torr to 3Torr. The chemical composition and structural properties of the deposited SiC thin films were analyzed by FTIR, XRD and Raman spectroscopy. The mechanical and tribological properties were evaluated through scratching test, friction, wear. The HMDSO films at 500 °C (H5) showed higher deposition rate, critical load and worn volume of the sphere, which suggests that this film has higher hardness and adhesion. The films obtained with HMDSO presented less friction coefficient values.

The results showed that the films presented amorphous structures (a-SiC:H) and those obtained with 500 °C and 3 Torr presented high adhesion and tribological performance.

Acknowledgments: This work was supported by CNPq, CAPES and FAPESP (Grant n^o 2011/50773-0).

References:

[1] WADA, A.;OGAKI,T.;NIIBE, M. Local structural analysis of a-SiCx:H films formed by decomposition of tetramethylsilane in microwave discharge flow of Ar.Diamond & Related Materials, University of Hyogo, Hyogo, Japan, p. 364-367. 2011.

[2] PORADA, O.K.; IVASHCHENKO, V.I.; IVASHCHENKO, L.A. a-SiC:H films as perspective wear-resistant coatings. Surface & Coatings Technology, NAS of Ukraine, Avtozavodska str. 2, 04074 Kyiv, Ukraine, p. 122–126.2004.

[3] RASHID, Nur Maisarah Abdul; RITIKOS, Richard; OTHMAN, Maisara. Amorphous silicon carbon films prepared by hybrid plasma enhanced chemical vapor/sputtering deposition system: Effects of r.f. power. Thin Solid Films, University Of Malaya, p. 459-463. 2013.

[4] MAGUIREA, P.D.; LAUGHLINA, J.A.; OKPALUGOA, T.I.T. Mechanical stability, corrosion performance and bioresponse of amorphous diamond-like carbon for medical stents and guidewires. Diamond & Related Materials, N. Ireland, United Kingdom, p. 1277–1288, 2005.

CrAl(La)N coatings with lanthanum content varying from 0 to 7.73at.% were deposited on cemented carbide substrates by using a plasma-assisted reactive magnetron sputtering process. The amounts of lanthanum were varied by controlling the sputtering rate of Cr30Al70 targets and lanthanum target. The effects of varying amounts of lanthanum addition on the microstructure and mechanical properties of CrAlN coatings were investigated. The results showed that cubic structure was formed in the coatings. The preferred orientation changed from (111) to (200) with lanthanum content increased. Much more sense and finer grained columnar crystals were observed with lanthanum addition, while amorphous morphology was detected in the Cr0.28Al0.64La0.08N, Cr0.28Al0.59La0.13N and Cr0.27Al0.57La0.16N coatings. The hardness increased from 27.4Gpa to 43.4Gpa when lanthanum was added; however, the hardness decreased to 29.4Gpa with a further increase in lanthanum content. According to the indentation adhesion test, Cr0.3Al0.07L0.03N showed the best adhesion strength.

Quaternary Ti-Al-Si-N films were deposited on AISI 304 stainless steel substrates by an inductively coupled plasma-assisted magnetron sputtering technique using Ti3Al and Si targets in an Ar/N₂ gas mixture. The microstructure and mechanical properties for the films were investigated as a function of deposition variables such as Si content and substrate bias voltage. As the Si was incorporated into Ti-Al-N film, the microstructure of Ti-Al-Si-N films were changed from a columnar structure with coarse grains to a glass-like structure with fine grains, and the micro-hardness of the Ti-Al-Si-N films showed higher hardness values compared with Ti-Al-N coating. The mechanical and tribological properties for the films were investigated in various Si contents. The microstructures of the synthesized films were characterized by X-ray diffractometer (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscope (XPS), high-resolution transmission electron microscope (HRTEM), respectively. Nano-indentation was conducted to assess the hardness and Young’s modulus of the films. Wear resistance and coefficient of friction of these films were evaluated using a micro-tribometer. This paper will present the effects of Si content on the microstructure, mechanical and tribological properties of inductively coupled plasma-assisted magnetron sputtered Ti-Al-Si-N films.

Carbon nitride (CNx) is one of promising hard and chemically stable coating materials because of having similar or higher properties as compared with diamond. However, the high electrical resistance of CNx thin films led to arcing and target poisoning during reactive sputtering process. In this study, CNx thin films were deposited by asymmetric bipolar pulsed DC (ABPD) magnetron sputtering and direct current (DC) magnetron sputtering technique. The change of bonding characteristics and corrosion resistance were investigated as types of power generator. The microstructure of deposited CNx thin films showed columnar structures with regardless of power generators. But the CNx film synthesized by DC magnetron sputtering showed a lot of macro CNx particles on surface, beside those particles were significantly decreased by using ABPD. And surface roughness, residual stress and defects were also decreased in ABPD sputtered CNx thin films. From the results of corrosion test, CNx thin film synthesized by ABPD magnetron sputtering showed superior resistances and low corrosion rates compared with a DC sputtered CNx thin film. Authors concluded that bonding characteristics of CNx thin films were effectively changed from low to higher fraction of sp³ bonding and more nitrogen contents in films by using asymmetric bipolar pulsed DC.

Nanocrystalline Aluminium-Zirconium coatings with Zr content between 0 and 25 at.% were deposited on high strength steel (HSS) by dc magnetron sputtering. Microstructure, microhardness and corrosion behaviour of Al-Zr coated steel were investigated.

For Zr content up 18 at.%, the characterisation of Al-Zr coatings by X-ray diffraction (XRD) shows the formation of fcc solid solution with nanocrystalline structure. From 18 at.% to 25 at.% Zr the Al-Zr coatings are amorphous single-phased. The increase of Zr content in coatings leads to a refinement of microstructure and to an increase of microhardness.

The corrosion behaviour of Al-Zr coatings was studied in 5 wt % NaCl solution using potentiodynamic polarisation, linear polarisation resistance and electrochemical impedance spectroscopy (EIS). The results show an enhancement of corrosion resistance and a decrease of corrosion kinetic with Zr contents’ increase. Lower corrosion rates are obtained for highest Zr contents. EIS results confirm the enhancement of corrosion resistance with addition of Zr and this enhancement is ascribed to the blocking mechanism due to ultra-dense structure of coating at high Zr contents.

The combined micro arc oxidation (MAO) and closed field unbalanced magnetron sputtering (CFUBMS) process was used to deposit duplex MAO/DLC coating on Cp-Ti alloy. Analysis of the microstructures, morphology and crystallographic structure were performed by using a SEM, RAMAN and XRD. The wear, corrosion and tribocorrosion properties of the coatings were investigated using the pin-on-disc wear test, potentiodynamic polarization test and combining tribocorrosion test unit, respectively. It is found that the DLC thin film could be successfully deposited onto the MAO coating. The results of this study showed that duplex MAO/DLC coatings exhibit better wear, corrosion and tribocorrosion properties than the DLC or MAO monolayer on Cp-Ti alloy substrate. MAO/DLC coatings exhibited dense structure. The dense microstructure is an important factor for the hardness. This causes an increase in the wear resistance. Duplex coatings were uniform, compact, smooth, columnar and dense as the Ti-DLC films that were directly coated onto the substrate. The MAO /DLC duplex coated has the hardest hardness value. The results also showed that MAO /DLC duplex coatings on Cp-Ti substrates increased the tribocorrosion resistance by acting as a barrier layer.

Carbide and nitride of transition elements are natural candidate materials for wear resistance applications as protective coatings. Extreme hardness, high wear resistance, low friction coefficient, chemicaly stability of transition metal(s) doped-diamond-like carbon (DLC) films make them popular. From this point of wiev, transition metals, Ti and Ta doped hydrogeneted DLC films were deposited by closed-field unbalanced magnetron sputtering system onto Ti6Al4V, Cp-Ti, AZ-91 magnesium and 2024 Aluminium alloys in Ar/N₂/C₂H₂ atmosphere. The tribocorrosion properties of Ti:Ta-based DLC coating were investigated. The coated specimens were characterizied by SEM, XPS and X-ray diffraction techniques. Hardness measurements was performed by microindendation. The results showed that Ti-Ta-doped DLC film shows very dense microstructure, high hardness and tribocorrosion resistance.