ICMCTF2016 Session BP: Symposium B Poster Session

The Diamond like carbon Protective films (DLC) have a great interest for the development of the automotive, aerospace, and metallurgical industry, as contact surfaces that require a low coefficient of friction and high mechanical resistance, DLC films meet these conditions. Many of the processes used for the growth of these films are, conventional methods of plasma treatments. In these cases, presents a high power consumption with high temperature and pressure, which affects the adhesion of the film to the substrate. For this reason it is possible to use ASP technique where conditions growth in a PECVD-DC Pulsed deposition system enhance the formation of plasmas. Being stable plasmas and plasma density higher, where it is possible to grow DLC films in extremely low pressure and temperature, however the lack of information on use of the technique of ASP for growth DLC films can develop a work about the effect of the distance between the screen and the sample. The purpose of this paper is to investigate this effect, growing DLC films on metal substrate using a 316 stainless steel screen. The layers were observed with SEM and Raman spectroscopy. The tribological behavior was analyzed by linearly reciprocating wear tests at room temperature. Adhesion was tested in accordance with the VDI3198 norm, based on a Rockwell C indentation test evaluation. The coatings registered a hardness of 20 GPa, showing better wear resistance and elevated adhesion,

Owing to their light-weight and tunable electrochemical characteristics, magnesium (Mg) alloys have attracted increasing interest for diverse technological applications ranging from structures, e.g., aviation/transportation to functions, e.g., biocompatible materials. To realize performance in these applications, improved understanding of the basic relationships among Mg-alloy processing, structure and properties is needed. In this study, thin film (<5 µm) magnesium-chromium (Mg-Cr) alloys were synthesized on quartz substrates by RF magnetron co-sputtering, yielding elemental compositions ranging from approximately 1 to 38 at% Cr. The films’ surface morphologies, crystalline structures and electrochemical behaviors were characterized using SEM, EDS, XRD and potentiodynamic polarization measurements. As the concentration of Cr in the films increased the grain size reduced, surface roughness decreased, and anodic polarization current densities decreased. XRD patterns show a shift to an increased value of 2ϴ for the Mg peak as Cr concentration increased. Observed relationships among alloy processing and structure, as well as alloy structure and properties are presented and discussed.

Tungsten oxide (WO₃), one among the transition metal oxides, is a wide band gap semiconductor with excellent physical, chemical and electronic properties. Recently, cation and anion doping of WO₃ is gaining significant attention in order to design materials suitable for application in solar energy conversion, photo-catalysis, transparent electrodes, electrochromics, and flat panel displays in optoelectronics. Recently, we demonstrated that controlled nitrogen chemistry and composition can facilitate the optical property tuning of t ungsten oxy-nitride (W-O-N) deposited by direct current (DC) sputtering. In this work, the structure, optical and mechanical property evolution of amorphous W-O-N films with variable nitrogen content post-deposition annealing was studied. Post-deposition annealing was performed in an inert atmosphere at 400 ^oC and 500 ^oC for a constant time of one hour. X-ray diffraction and electron microscopy results indicate that the W-O-N films remain amorphous. However, changes in chemical composition, optical and mechanical properties are evident indicating that the thermal induced changes are at nanometric structure of the films. Optically, spectrophotometry results showed a strong correlation between transmission magnitude and band gap (E_g) results, and the nitrogen content in the films. Band gap results show a steady decrease in value between 2.72 eV and 1.88 eV indicating a transition from WO₃ like behavior to that of a W-O-N system and when compared to the results of non-annealed samples the values drop across all compositions. Ellipsometry results corroborate with spectrophotometry analyses. X-ray photoelectron spectroscopy (XPS) measurements indicate that there was a loss in nitrogen content after the annealing process which could be correlated to the loss in E_g values. Mechanical characterization using nano-indentation indicate that the hardness and Young’s moduli are higher in annealed W-O-N films than as-deposited films in corroboration with changes in nanometric structure of the films. Results will be presented to show that the improved mechanical properties of annealed W-O-N films coupled with changes in optical properties can be useful for application in optical devices, specifically the filters.

By means of pulsed laser deposition, a CdO film was grown onto a glass substrate at room temperature. The mean kinetic energy and the ion density of the laser produced plasma were 75 eV and 13.5 x 10^-12 cm^-3 respectively. A laser fluence value of 2 J/cm² was used. The film was thermally treated at 500 ºC in air, in order to see the effect of annealing on its physical properties. The structural properties of the as-grown film indicate that a (200) highly oriented polycrystalline cubic sample was obtained, which was confirmed by transmission electron microscopy. The annealed sample is still cubic but it is no longer oriented in the (200) direction. A reduction in grain size for the annealed sample was observed by scanning electron microscopy. Raman spectroscopy revealed the typical second order vibrational modes of cadmium oxide which are related to defects. XPS results show the presence of CdO together with a substoichiometric CdO_x phase for the as-grown sample. For the annealed sample a compensation of oxygen vacancies. Electrical resistivity measurements give a value of 8.602 x10^-4 (Ω cm) for the as-grown film which is in excellent agreement for cadmium oxide films obtained by physical vapor deposition techniques. For the annealed sample the electrical resistivity increased to a value of 9.996 x 10^-3 (Ω cm). The as-grown sample has zero transmission in the UV-Visible range as shown by optical transmission measurements. The photoluminescence spectra of the samples were measured in order to shed some light on the origin of the zero transmission result.

The CrZrSiN nanocomposite coatings have been paid much attention to the cutting tool’s coating applications due to their excellent properties such as high hardness, low surface roughness, and excellent thermal stability. The hardness of coating was enhanced as the bilayer period increased to a certain level, and in this work the influence of bilayer periods on mechanical properties of the CrZrSiN coating was investigated.

The CrZrSiN/CrZrN/CrN multilayer coatings were synthesized using the unbalanced magnetron sputtering system on tungsten carbide disc type substrate, and the bilayer periods of the CrZrSiN/CrZrN upper layer were controlled in the range of 680 to 340 nm. The microstructure, hardness and elastic modulus, and friction coefficient of the CrZrSiN/CrZrN/CrN multilayer coatings were evaluated by field-emission scanning electron microscopy (FE-SEM), nano-indentation, and ball-on-disc type wear tester, respectively. All the coatings were annealed at temperatures from 600 to 1000˚C in furnace for 30 min, and the hardness values were investigated using nano-indentation.

The hardness and elastic modulus of all the CrZrSiN/CrZrN/CrN coatings gradually increased from 28.5 to 32.0 GPa, and 268 to 281 GPa as decreasing of the bilayer period, respectively. The friction coefficient showed the lowest value of 0.27 on the coating with bilayer period of 340 nm. The hardness values of all the coatings were maintained up to 1000˚C, and the thermal stability were not affected significantly by the bilayer period. This improved hardness could be attributed to the dislocation blocking effect at the layer interfaces due to difference in the shear moduli of the individual layer materials between the CrZrSiN and CrZrN, and this led wear resistance enhancement of the CrZrSiN/CrZrN/CrN coating.

For over a century, Zn coating has been widely used to protect steel from corrosion. Recently,economic and environmental considerations have led to efforts to develop high performance Zn based coatings with decreasing coating thickness and increasing corrosion resistance.

The Zn/Mg/Zn multi-layer coatings were synthesized on cold-rolled steel substrates, and the annealing were carried out at 100, 200 and 300 ^oC for 1 hour in the vacuum furnace to form the Zn and Mg intermetallic phases. The effect of annealing treatments on the corrosion resistance of the Zn/Mg/Zn coatings was investigated using salt spray test (SST) and potentiodynamic polarization measurement. The microstructure of the surface, the chemical composition and the crystal phase of the Zn/Mg/Zn coatings were investigated using the field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD).

The XRD results showed MgZn₂ phases was mainly formed in the Zn/Mg/Zn coatings after the annealing treatment at 100 and 200 ^oC. After the annealing treatment at 300 ^oC, MgZn phases were formed mainly in the Zn/Mg/Zn coatings, and the potentiodynamic polarization measurements results revealed that Zn/Mg/Zn coatings contained MgZn phases showed lower corrosion potential and higher corrosion current density than others. The formation of MgZnphases could be attributed to decrease corrosion resistance.

The purposes of this study were to search for the optimum conditions for the thin film deposition process by unbalanced magnetron sputtering (UBMS) method and identify the most sensitive processing parameters for the deposition of VN thin films by using Taguchi design of experiment (DOE) method. In this study, VN films were deposited on Si (100) substrates by UBMS with different deposition parameters. Four major parameters of an UBMS system, including substrate bias, nitrogen flow rate, substrate temperature, and dc target gun power, were selected for optimizing the deposition process. After deposition, X-ray diffraction (XRD) was used to characterize the structure and field emission gun scanning electron microscopy (FEG-SEM) were used to observe the microstructure of the specimens. The hardness and the electrical resistivity of the VN thin films were determined by nanoindentation and four-point probe, respectively. The analysis of mean (ANOM) and analysis of variance (ANOVA) were carried out to assess the sensitive parameters and predict the optimum conditions. Hardness and electrical resistivity of thin films were chosen as the indexes for the property optimization. Based on the statistical analysis, the most sensitive parameters of the deposition process were found to be target gun power and substrate temperature. Using the optimum deposition conditions, VN films on Si (100) substrates with high hardness and low electrical resistivity were successfully produced. In addition, further optimization of the deposition process can be conducted by fine tuning the sensitive parameters.

Coatings with nanoscale architectures, such as nanocomposites or nanolaminates, offer improved mechanical properties and resistance to radiation environments due to their increased interface area per unit volume [1-2]. Superhard coatings based on Ti-Si-N system have attracted considerable interest in the last decade. Hardness enhancement was reported in TiN/a-Si₃N₄ nanocomposites [3] as well as TiN/SiN_x multilayered films [4] and the origin of this behavior was attributed to higher interfacial bond strength, in which Si atoms are tetrahedrally coordinated to N atoms or resulting from stabilization of a metastable cubic SiN phase.

In the present work we have studied the structural and mechanical properties of ZrN/SiN_x nanolaminated films. Samples were grown at 350°C on Si and MgO (001) substrates by alternate reactive magnetron sputter-deposition of ZrN and SiN_x layers with different thickness ratios: a first series, where the ZrN thickness was fixed at 10 nm, and the thickness of SiN_x varied between 0.4 and 20 nm, and a second series where the SiN_x thickness was fixed at 5 nm and the thickness of ZrN varied between 5 and 40 nm. XRD, XRR and RBS were used to characterize the structure and compositional modulation periodicity, while mechanical properties were measured using nanoindentation. The stress state was determined using both in situ wafer curvature and ex situ XRD using sin²y method. Compared to monolithic (111)-oriented ZrN film, multilayers exhibited a (002) preferred orientation. The maximum hardness of 24.3 ± 1.6 GPa was obtained for the multilayer with the lowest SiN_x thickness (0.4 nm) due to formation of coherent interface. In this case, pseudomorphic forces act to stabilize a cubic crystalline silicon nitride interfacial phase, resulting in a cube on cube epitaxial growth of the ZrN/SiN_x multilayer on MgO (001).

1. I.A. Saladukhin, G. Abadias, A. Michel et al., Thin Solid Films 581 (2015) 25

2. V.V. Uglov, G. Abadias, S.V. Zlotski et al., J. Surf. Invest.: X-ray, Synchr. and Neutr. Techn. 9 (2015) 995

3. S. Hao, B. Delley, S. Veprek, C. Stampfl, Phys. Rev. Lett. 97 (2006) 086102

4. L. Hultman, J. Bareñon A. Flink et al., Phys. Rev. B 75 (2007) 155437

TiAlN hard protective coatings for high-speed cutting and machining applications are developed to withstand a broad range of thermal, mechanical and chemical loads. In this study microstructure and properties of Ti_1-xAl_xN coatings with x > 0.8 prepared using moderate temperature chemical vapour deposition are described. The coatings characterization was performed by X-ray nanodiffraction diffraction and transmission electron microscopy techniques.

The structure of films consists of nano-sized grains with high level of self-organization (nanolamellae), detected constituents are cubic TiN and hexagonal AlN. The films exhibit exceptional performance, specifically high mechanical hardness and extraordinary high oxidation resistance (up to 1.100 °C).

Combinatorial materials design of thin films allows for the investigation of fundamental nanomechanic relationships and optimization of thin films for engineering applications. Using a unique deposition chamber that combines magnetron sputtering, e-beam evaporation, nanoparticle deposition and atomic layer deposition (ALD), the architectural design of thin films can be tailored to study multiple physical and chemical properties. One unique ability of this deposition chamber uses a nanoparticle generator in combination with the PVD system, to deposit particles which would not normally precipitate from a solid-solution such as from two completely miscible systems or completely incompatible materials. From dispersion strengthening of miscible systems, a comparison between solid-solution strengthening versus particle strengthening is possible in the range of volume fractions which cannot be achieved in precipitation strengthened materials. Two material systems were chosen for this investigation to observe the effect of “hard” versus “soft” particle strengthening: Nb-W and Nb-V. The nanoparticle generator uses an adaptation of traditional magnetron sputtering to force agglomeration of the sputtered ions into small particles ranging from 5 to 20 nm in diameter. The nanoparticle volume fraction was consistent at approximately 5 vol% for both films with similar particle size. Co-sputtering with a traditional magnetron source allows for these particles to be evenly dispersed throughout the film. Solid-solution alloys of both systems were also deposited at 5 vol% and compared to the nanoparticle strengthened films using the same techniques. The microstructure, particle size and density were characterized using scanning transmission electron microscopy (STEM) and transmission Kikuchi diffraction (TKD) and correlated to the modulus and strength determined using micro-pillar compression testing. An additional chamber mounted to the system allows for in-line ALD, adding the capability for interface engineering using ceramic layers with sub-nanometer thickness control. Initial studies of this capability have focused on systems where multiple PVD cycles are interrupt with very thin ceramic ALD layers to control dislocation propagation in the thin film system. Multilayer films of PVD sputtered Cu and thin Al₂O₃ ALD films are tested using micro-pillar compression to determine the resulting mechanical properties and deformation characteristics of this newly designed film. Previous work on a trilayer film has shown this configuration has the ability to confine deformation in one layer, suggesting a similar mechanism will preside in a multilayer system.

In this study is showed the formation of multilayer with boron and carbon in low carbon steel. The process was obtained by two treatments thermochemical, using a combination boronized and cementation both by pack process, without atmosphere controlled. The boron diffusion with paste dehydrated at 1273 K temperature for 8 h exposure; after diffusion carbon were performed with coke and carbon vegetable at 1173 K temperature for 12, 14, 16 and 18 h of exposure. The multilayer formation was characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy EDS and x-ray diffraction (XRD). The gradient micro hardness and modulus of elasticity is obtained in nanoindentation tests using ISO 14577-1 norm, with a constant load from the surface to the substrate for each condition. In this work is obtained multilayer in the first stage showed a layer sawn with boro and the second stage showed a layer flat with carbon. The results showed the modification surface in this steel, also a new layers and change of properties in comparison to boronized layers

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 (lube free die casting). In this research, a simple and direct testing approach, the aluminum adhesion test (AAT), was developed that enables semi-quantitative measurements of the soldering behavior (adhesion behavior) between the die casting alloys and the coated dies. Various CrN-based coatings prepared either by magnetron sputtering or by cathodic arc evaporation were tested by the AAT. The alloy/coating interfaces are examined by using optical microscopy, scanning electron microscopy, focused ion beam and transmission electron microscopy. Several possible causes are suggested to account for the different adhesive behaviors.

Ti6Al4V have been used typically for several applications in biomedical and aerospace industries due to its several valuable properties, such as high specific strength, good corrosion resistance and biocompatibility. However, its tribological properties are known to be poor. DLC coatings have been used to overcome these problems. This work shows a study of the adhesion between a DLC film and a Ti6Al4V substrate using a silicon interlayer by pulsed DC-PECVD deposition. Different pulsed DC voltages (in a range from -2 kV to -12 kV) were applied to get different case studies. Characterization of the films was performed using Raman spectroscopy, scanning electron microscopy (SEM), Rockwell C indentation test, and scratch test. Results exhibit how the variation of the pulsed DC voltage affects the silicon interlayer, and consequently, the adhesion between coating and substrate. Then, best conditions for no delamination of the coating were identified.

This contribution will outline recent progress made in applying nanostructured PVD coatings for fine blanking applications.

Compared to the common blanking process, pieces produced from steel sheets by fine blanking do not need any further finishing steps, due to the clean cut with minimized fracture. Therefore, fine blanking is well adapted for the production of high numbers of pieces with tight tolerances and delicate features. However this process challenges the tool material due to the tight cutting gap, especially when cutting thick or strong steel sheets. Commonly this process is run using powder-metallurgical steel punches. Changing the tool material to cemented carbide frequently causes problems on the tool edges, especially due to the tensile stresses encountered during retracting the punch.

Ti-based coatings offer a basic wear protection for this kind of application. However nano-layered Cr-based coatings such as AlCrN or AlCrTiN deposited using a PVD process with cylindrical rotating cathodes, both on PM steel and cemented carbide are showing higher performance.

These coatings can be produced with good adhesion even on complex tool shapes, thanks to an optimized plasma etching. They also offer a low surface roughness and a lower coefficient of friction versus steel compared to the uncoated cemented carbide. For critical materials, an optional aluminum-free low-friction top layer can be added.

The coatings were deposited using the high-performance PVD coating unit π411 and the recently announced π1511 unit, both equipped with the unique cylindrical rotating arc cathodes.

In field tests, Cr-based coatings increased the tool life of cemented carbide fine blanking active elements by a factor of 10 compared to the lifetime of coated steel elements. The tools wear was studied in depth by SEM analysis. As evident from the wear analysis, the optimized toughness of the dedicated nano-layered coatings prevents cracking, the most commonly failure mechanism found in fine blanking.

We investigated the structure and mechanical properties of ZrCu metallic glass and ZrCuON thin films deposited on a silicon substrate by rf magnetron sputtering from a Zr₅₀Cu₅₀ target in Ar or Ar+N₂ plasma discharge, respectively. Process parameters such as rf power, Ar and N₂ flows, and deposition time were varied and experimental conditions for glass forming ability identified. Their influence on the thickness, the films microstructures, the chemical composition and the mechanical properties were explored. The structural properties of the metallic glass and nitride compounds were characterized by X-ray diffraction and X-ray reflectivity. The chemical composition was investigated by both wavelength-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy leading to bulk and surface insights, respectively. The picosecond ultrasonics, the Brillouin light scattering and the nanoindentation techniques were employed to measure their acoustic, elastic and hardness properties whereas nanoscratch tests evaluated their adhesion performance. Predicted ductility/brittleness of the films was first inferred from their measured elastic properties using the Pugh [1] (shear modulus over bulk modulus G/B) and the Pettifor [2] (Cauchy pressure p = C₁₂-C₄₄) criteria. We also used the ‘cooperation parameter’ d, related to the Poisson ratio ν, and recently proposed by Liu et al. [3] to discuss the ductility/brittleness property of the films.

[1] S.F. Pugh, Philos. Mag., 45 (1954) 823-843.

[2] D. G. Pettifor, Mater. Sci. Technol., 8(4) (1992) 345-349.

[3] Z.Q. Liu, W.H. Wang, M.Q. Jiang, Z.F. Zhang, Philosophical Magazine Letters, 94(10) (2014) 658-668.

Diamond-like Carbon (DLC) coatings have excellent physical properties such as, low friction, high wear resistance and high hardness. In mechanical engineering, low friction signifies a lower loss of energy, higher reliability and a better wear resistance. Due to these properties the DLC film is interesting for the industrial application such as bio technology, molds, tools and mechanic parts etc. The DLC films have an amorphous structure unlike diamond and graphite. The bonding structures are included that sp³ (diamond-like or tetrahedral bond), sp² (graphite-like or trigonal bond) and sp¹ hybridization C-C bond. DLC thin films have adjust comparative ratio of bonds and show various mechanical properties through deposition methods or interlayers. The aim of this study was to determine the influence of CrN, CrC, TiN and TiC buffer layers on the mechanical properties of Diamond-like Carbon coatings deposited on WC-Co alloy. The interlayers were deposited by magnetron sputtering and the DLC films deposited by linear ion source. The characteristics of the films were investigated using Nano-indentation, Micro Raman spectroscopy, Field Emission-Scanning Electron Microscopy (FE-SEM) and X-ray Photoelectron Spectroscopy (XPS), residual stress tester and scratch tester.

Diamond-Like Carbon (DLC) film has excellent material properties such as chemical stability, high hardness, low friction, and so on. In the tribology field, the DLC films are expected to be applied to sliding parts of cars due to its excellent features. It has been reported that the friction coefficient of the DLC film was remarkably reduced by doping silicon atoms. The hydrogen-free DLC film can also realize the reduction of the friction coefficient and is deposited by using the magnetron sputtering method. It is important to diagnose gas-phase and surface reactions to clarify the deposition mechanisms and achieve the low friction coefficient. In this study, Si-doped DLC film was deposited with a magnetron sputtering method using Si-contained carbon target.

The RF magnetron sputtering apparatus was used for the film deposition. The total pressure of Ar gas was 0.5Pa, the flow rate was 100sccm, RF power was 150W and bias voltage was changed from -50V to -200V. The distance between the target and the substrate was 50mm. The target was 2-inch carbon containing silicon of 5%. The crystal structure of the deposited Si-doped DLC film was measured with a microscopic laser Raman spectroscopy. Si content of the DLC film was measured with energy dispersive x-ray spectroscopy (EDX).

The Raman spectra of the Si-doped DLC films for different bias voltages were measurend. The intensity ratio of the D and G band (I(D)/I(G)) decreased with increasing negative bias voltage up to -150V and then I(D)/I(G) increased over -200V. This result shows that the disorder component was eliminated by the Ar ion bombard. Deposition rate increased with increasing bias voltage up to -100V and saturated. This result shows that deposition was assisted by the Ar ion bombard. On the other hand, Si content decreased with increasing bias voltage. The relation between Si content and bias voltage will be discussed in the detail.

This work reports on the technological possibilities of magnetron sputtering system with "hot" target in case of deposition of metal coatings. The deposition modes of magnetron sputtering system with "hot" target on the example of titanium films are determined in wide range of operation frequency of power supply and fill ratio of impulse.

Atomic-force microscopy, XRD and adhesion investigations of experimental samples were studied.

The advantages and drawbacks of magneton with "hot" target were discussed.

Recent research into plasma assisted PVD of Chromium- and/or Titanium-based metallic coatings has demonstrated that (with appropriate alloying additions) high values of hardness (≥ 12-15 GPa) and low Young’s modulus (≤150GPa) can be achieved. According to the H/E criterion for tribo-coating mechanical property optimisation, this results in coatings with enhanced toughness and a long elastic strain to failure, with an ability to better accommodate surface loads and consequential substrate deformations. This behaviour is a consequence of the generation of nanocrystalline or mixed crystalline/amorphous phases in the deposited coating (either during, or after deposition – eg. by post-coat annealing and/or devitrification).

However, although such coatings demonstrate excellent tribological performance, they may exhibit relatively poor corrosion behaviour – particularly in regard to the galvanic/sacrificial corrosion protection which they provide to typical steel (or light-alloy) substrate materials. One means by which the corrosion protection characteristics can be improved is by careful adjustment of the open-circuit potential of the coating. In this regard, aluminium-based metallic coatings offer distinct advantages compared to Cr and Ti-based coatings.

TiNi shape memory thin film’s application area is gradually increasing. Especially MEMS applications of TiNi film, such as micro-mirror, micro-pump and micro-actuator are widely used. Adhesion to the substrate and fatigue resistance of the films are particularly important for these applications. At this study, we were investigated adhesion and fatigue properties of martensite and austenite phases of TiNi shape memory thin films. TiNi films deposited on copper and Si wafers by magnetron sputtering. Structural properties of the films determined via SEM, XRD and EDS analyses. Adhesion and fatigue properties of the films investigated with progressive and multi-pass scratch tests. Phase transformation temperatures and hysteresis were observed by differential scanning calorimeter (DSC). Scratch test results showed that adhesion and fatigue resistance of austenite phase is higher than martensite phase of TiNi film.

Process modelling should be based on a sound thermodynamic basis if temperature is high enough to allow reaching equilibrium. While thin films produced in PVD processes are usually far from equilibrium, it is pointed out here that there are many (para)equilibria during PVD processing. Paraequilibrium refers to a state where not all species are allowed to diffuse thus resulting only in a local minimum of Gibbs energy. The following processes are discussed using the FactSage software package [1]:

1) Vapor and plasma generation at cathodic arc cathodes

The energy dissipated per evaporated mass is calculated from reported target erosion rates and arc voltages (e.g. 500 kJ/g Cu) [2,3]. For comparison the energy needed to evaporate a solid metal is calculated and found to be 1-2 orders of magnitude smaller than the energy dissipated in an arc discharge (e.g. 6 kJ/g Cu). This is surprising, given that there is an empirical correlation between cohesive energy and burning voltage [3]. Considering only singly charged ions, it can be estimated that an energy input of 15 kJ/g Cu already results in a vapor temperature around 9000 K and an ion to neutral ratio ~0.6.

2) Phase evolution at the cathodic arc cathode

Numerous groups are working on understanding phase evolution at the cathode, especially focusing on AlCr cathodes [4,5]. While the solubility limit of Cr in the fcc phase is only around 0.03 at.%, Ramm et al. have reported up to 2.6 at.% Cr in an fcc solid solution [4]. Here, using paraequilibrium calculations a maximum solubility limit of up to 3.7 at.% Cr in the fcc solid solution is predicted. Furthermore, it is shown that simple extrapolation from pure substances overestimates the vapor pressure of e.g. Cr in an Al70Cr30 liquid by a factor of 2.5.

3) Non-metal content during reactive deposition.

Metal vacancies are responsible for the low thermal stability of TiAlN coatings reported in the last decades [6]. The variation of metal vacancy concentration in (Ti,Al,Va)N with Ti/Al ratio is predicted based on published DFT data. Good agreement with experiments corroborates that a paraequilibrium between nitrogen in the gas phase and nitrogen activity in the growing film is responsible for the amount of metal vacancies formed.

[1] Bale et al., Calphad 26 (2002) 189. http://gtt.mch.rwth-aachen.de/gtt-web/factsage

[2] Anders et al., XXIst ISDEIV Proceedings 1 (2004) 272.

[3] Anders et al., J. Appl. Phys. 89 (2001) 7764.

[4] Ramm et al., SCT 205 (2010) 1356.

[5] Franz et al., JVSTA 34 (2016) 021304.

[6] to Baben et al., talk B6-12

Ti_1-xAl_xN is commonly used as protective coating for, e.g., cutting or forming applications due to its outstanding properties like high mechanical strength and thermal stability. Ever growing demands in process efficiency and precision are in need for application-specific adjustments of already well established coating systems. Thereby, for instance, higher working speeds and increased processing temperatures are accessible. Additional factors determining the coatings’ performance during many applications are their tribological behaviour and wear resistance. The addition of molybdenum (Mo), tungsten (W), or vanadium (V), is known to significantly enhance the wear resistance of Ti_1-xAl_xN.

Here, we study in detail the influence of Mo additions to Ti_1-xAl_xN coatings on their mechanical properties and thermal stability. The films were prepared by cathodic arc evaporation using powder-metallurgically manufactured

(Ti_0.5Al_0.5)_(1-x)Mo_x targets with Mo contents x of 2, 5, and 10 at.%, and applying either -40, -80, and -120 V substrate bias.

The coatings are slightly overstoichiometric with nitrogen contents of 54 at.%, for all bias potentials used. The ratio of Ti, Al, and Mo within the coatings corresponds to the cathode composition. However, the growth morphology and microstructure of the coatings prepared, significantly depend on the Mo content. Our results clearly show that by the addition of Mo not only the hardness of Ti_0.5Al_0.5N increases but also their thermal stability.

In the present work, low temperature active screen plasma nitriding of a 17-4 PH precipitation hardening stainless steel was investigated. The active screen technique has been used to avoid undesirable plasma concentration, edge effects and arching during D/C plasma nitriding. Solubilized (S) and solubilized and aged (S+A) 17-4PH stainless steel samples were Active Screen Plasma Nitrided (ASPN) for 20 hours at low temperature (400°C) in order to avoid undesirable precipitation of chromium nitrides. Formation of these nitrides impairs corrosion resistance of the steel because they act as Cr sinks, reducing the overall amount of Cr available in the matrix. The main objective of this work was to characterize the effect of the starting conditions on the microstructure of the nitrided layers. Besides, the chemical gradients and hardness evolution during low-temperature, long term active screen plasma nitriding were also studied.

After the nitriding process, a homogeneous nitrided layer was obtained along the entire surface. Hardness measurements along the nitrided surface did not show relevant dispersion of values, indicating that ASPN was effective to avoid edge effects. Moreover, the nitrided layer could not be etched by Villela reagent, revealing that the corrosion resistance was not impaired.

X-ray diffraction patterns showed, for both starting conditions (S) and (S+A), expanded martensite peaks broadened and shifted to lower 2θ angles — compared to the martensite peaks of the substrate — indicating nitrogen supersaturation after plasma nitriding. The nitrided layer of the (S+A) specimen was thicker (9.2μm) than the nitrided layer of the (S) specimen (5.7μm). The maximum nitrogen content (measured by WDX) of the (S+A) specimen (3.7%) was greater than the maximum nitrogen content measured on the (S) specimen (1.9%). This difference in the nitrogen pick-up was reflected in greater hardness values for the (S+A) specimens (max. hardness 1130HV) in comparison with the (S) condition (max. hardness 950HV).

The later results were discussed in terms of the effect of Cu in the activity of Fe-N solid solutions. Thermo-Calc® simulations showed that when copper is in solid solution, it increases the nitrogen activity in iron-nitrogen alloys, decreasing the maximum nitrogen solubility in the steel. On the other hand, when copper is precipitated as nanoparticles in the matrix — as in the (S+A) condition — nitrogen activity decreases, implying in a greater solubility of nitrogen.

The substrate hardness after ageing was not changed by the 400°C/20 hours nitriding treatment, indicating that the surface treatment can be carried out without affecting the bulk properties.

Magnesium and its alloys are used in the fields such as biomedicine, automobile industry, defense industry and mainly in the aviation industry by the reason of having high strength and extremely low weight. However, it demonstrates low resistance to corrosion in aggressive environments because of chemical reactivity. Therefore the surface treatment is performed by the aim of improving this property of magnesium alloys.

In this study, AZ91 magnesium alloy is coated by the using of micro-arc oxidation (MAO) method which has recently increased. Following the coating process, the effects of pulse duration (duty time) and processing time on the surface morphology, corrosion resistance and phase structure of the coating were examined. To investigate the thickness values and microstructure of the coating, scanning electron microscope (SEM) was used, beside this to investigate coating phase structure X-ray diffraction (XRD) was used. Corrosion tests were performed in 3.5 % NaCI solution by using of VersaSTAT3 Potentiostattest equipment. Potentiodynamic polarization tests were used for corrosion analysis.

As a result; the effects of the pulse duration (duty time) on the phase structure of the coating has appared by the increasing of processing time. The increase of duty time has caused large pores and cracks in the surface morphology of the coating and at the same time this has caused a decrease in corrosion resistance of the coating. The increase of the processing time has improved corrosion resistance. The best corrosion resistance has been observed in R4 coating which has 50 µs pulse duration and 15 minutes processing time.