ICMCTF2016 Session B4-1: Properties and Characterization of Hard Coatings and Surfaces

Wednesday, April 27, 2016 2:10 PM in Room San Diego

Wednesday Afternoon

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2:10 PM B4-1-3 Elastic Constants of Binary Nitride Epitaxial Thin Films MeN (Me= Ti, Zr, V, Nb and Ta): Thin Film Growth and Ab Initio Calculations
Grégory Abadias (Institut P’, CNRS – ENSMA - Université de Poitiers, France); Philippe Djemia (LSPM-CNRS, France); Laurent Belliard (UPMC, Paris, France); David Tingaud (LSPM-CNRS, France); Fei Wang, Ferenc Tasnadi (Linköping University, IFM, Sweden)
Transition metal nitrides have been extensively studied in the last decades, owing to their excellent performance. For most of the applications, the thermal stability and the elastic properties are of great interest to deal with the durability of the material under service. Several coatings of multinary alloys have been proposed in order to improve their properties, one of them being widely used, is the ternary alloy TiAlN. Many other transition metal elements such as: Zr, V, Nb, Ta, … can be added to this ternary alloy or combined to design new properties of nitrides coatings. Assessing the elastic properties of polycrystalline multinary alloys remains challenging as they relate on many attributes: the phase composition, texture, existence of defects. Strategies should be employed to tackle this challenge, e.g. by studying systems of increasing degree of complexity. This is the aim of the present work dedicated to cubic single-crystal binary nitride thin films. TiN, VN, ZrN, NbN and TaN films were deposited by magnetron sputtering under reactive Ar+N2 plasma discharges on a MgO(001), (110) and (111)- oriented substrates, at a temperature of either 350 or 650°C. The working pressure was adjusted in the 0.20-0.65 Pa range, depending on the deposited material, to minimize excessive compressive stress levels in the films. In parallel, ab initio calculations were performed in the framework of the density functional theory using the VASP software. The thickness and mass density were determined by x-ray reflectivity measurements, while x-ray diffraction pole figure and reciprocal space maps were employed to study epitaxial orientation and determine lattice parameters. Elastic constants of thin films can be accurately studied by photoacoustic measurements. The Brillouin light scattering (BLS) technique allows measuring sound velocity of a few kinds of surface acoustic waves (VSAW) in thin films and thus estimating single-crystal elastic constants (rV2), in the case of epitaxial films, if the mass density r of the film is known. The Rayleigh surface wave is much more dependent on the shear elastic constant C44, thus BLS can provide at least this constant. It is well adapted for thin films and can be conveniently combined with the picosecond ultrasonics technique that measures the sound velocity of longitudinal waves (VL) that are travelling forth and back within the film along the direction perpendicular to the film plane, i.e. [001], [110] and [111] crystallographic directions. We used this combination of techniques to measure the elastic constants C11, C12 and C44 of our epitaxial nitride films.
2:30 PM B4-1-4 Influence of Nitrogen Concentration on Hardness and Thermal Properties of Cr-N Thin Films
Camille Pallier, Grzegorz Greczynski, Per Eklund (Thin Film Physics Division, IFM, Linköping University, Sweden)

Due to their high hardness and strong oxidation resistance, transition metal nitrides, such as CrN, are common materials for hard coatings applications [1]. A new approach to enhance their performance relies on optimizing their thermal conductivity in order to lower the substrate temperature during operation and, hence, reduce the thermal gradient between the coating and the substrate [2].

A previous work revealed that CrNx (x≥ 0.05) showed good mechanical properties even at low at% nitrogen content due to a reduced grain size and the presence of point defects in the Cr structure [3]. As the hardness is stable with increasing N concentration, it seems relevant to establish a correlation between nitrogen content and thermal conductivity.

In this study, CrNx thin films were deposited by reactive DC magnetron sputtering at 200oC in N2/Ar gas mixtures with the N2/Ar flow ratio varying from 0.02 to 0.3, while the total pressure was fixed at 5 mTorr. The resulting films are characterized by θ-2θ X-ray diffraction, together with X-ray photoelectron spectroscopy, SEM and TEM. As analyses revealed that the substrate bias Vs and Cr-target power Pdc influence the composition and the nanostructure of the CrNx films, we focused our study on the effect of both Vs and Pdc on film hardness and thermal properties. A correlation between nitrogen content, hardness and thermal properties is then established.

[1] Hones et al., J. Phys. D: Appl. Phys. 36 (2003) 1023

[2] Böttger et al., Thin Solid Films 549 (2013) 232

[3] Greczynski et al., IEEE Trans. Plasma Sci. 38 11 (2010) 3046

2:50 PM B4-1-5 Ion Assisted Deposition of Thick Multifunctional Tribological Coatings by Deep Oscillation Magnetron Sputtering with Filament Assistance
Jianliang Lin, Ronghua Wei (Southwest Research Institute, USA); William Sproul (Reactive Sputtering, Inc. USA)

Plasma enhanced magnetron sputtering (PEMS) is an advanced version of the traditional magnetron sputtering technique by introducing an extra global plasma generated by an electron source, e.g. hot filaments, to enhance ionization in the entire vacuum chamber. Deep oscillation magnetron sputtering (DOMS) is one version of high power impulse magnetron sputtering (HiPIMS) technique that uses large voltage oscillation packets to achieve high power pulses for magnetron sputtering. DOMS has shown interesting capabilities in generating virtually arc-free high power pulsed depositions for reactive sputtering. Both the DOMS and PEMS techniques aim at increasing the degree of ionization and plasma density, which can be usefully utilized to improve the structure and properties of the coatings.

In the first part of the presentation, the fundamental and technical aspects of the two technologies will be introduced. Plasma diagnostics indicate the two technologies show different dominating ion species and ion energies. The PEMS process generates a large amount of low energy gas ions, while the DOMS process introduces ionized metal target ions with a distribution of ion energies. A combination of the two technologies was found to be a powerful tool for the deposition of dense, low stress, thick multifunctional tribological coatings for high performance tribological applications that demand multifunctional properties, e.g., high wear and erosion resistance coupled to low coefficient of friction, good toughness, and increased adhesion to the substrate. An increased coating thickness will also provide for greater protection of the substrate in harsh environments.

In the second part of the presentation, recent development and applications of thick CrAlN (up to 25 μm), TiSiCN (up to 30 μm), and DLC (up to 10 μm) coatings by DOMS and PEMS for wear and solid particle erosion protection, and automotive engine friction reduction will be reported. It was found that the PEMS assistance affected the target hysteresis behavior and the reactive sputtering process stability. The low energy ions and high deposition temperature associated with the PEMS assistance effectively reduced the residual stress of thick coatings and improved the coating adhesion. By controlling the peak target power in DOMS and/or the filament discharge current in PEMS, the substrate ion currents are tens of times higher than in conventional magnetron sputtering. These thick coatings exhibited extremely dense microstructure and improved mechanical and tribological properties as compared to the coatings grown by conventional magnetron sputtering.

3:30 PM B4-1-7 Composition, Morphology and Mechanical Properties of B‑C‑W and B‑C‑Ti Thin Films Prepared by Pulse Magnetron Sputtering
Martin Friedemann, Heidrun Klostermann (Fraunhofer FEP, Germany)

In the present work, coatings in the material systems B-C-W and B-C-Ti have been synthesized by pulse magnetron sputtering, to exploit their potential as coatings for hard, wear resistant applications. These layers offer interesting properties, because of the possible amounts of carbides and borides that can form in the non-equilibrium deposition processes. Especially the amount of tungsten in the layers promises high wear resistance and corrosion protection at elevated temperatures.

The B‑C‑W and B‑C‑Ti thin films have been deposited by pulsed magnetron co-sputtering in bipolar mode, using a boron carbide (B4C) target and a metal target (Ti or W) with a maximum power input of 18.75 W/cm². The films have been deposited onto various steel substrates at 300 °C and at a pressure of about 0.5 Pa. The amount of metal in the layers has been varied by adjusting the sputtering pulse length of the respective target material. The influence of bias voltage on the coating properties and the influence of an adhesion promoting metal rich layer between the substrate and the top layer have been investigated.

The coating adhesion has been examined by scratch tests. The hardness and the Young's modulus of the layers have been determined by nanoindentation. Their composition has been analysed by using the optical glow discharge emission spectroscopy (GD OES) and the ion beam analysis.

Whereas the majority of coatings exhibits hardness around 20 GPa or lower, maximum hardness of 28 GPa and Young’s modulus of 420 GPa are observed in a certain compositional range, in which coatings also distinguish by good thermal stability.

3:50 PM B4-1-8 Effect of Grain Size on Surface Evolution of Ti0.5Al0.5–Cathode during Cathodic Arc Deposition of TiAlN Coatings
Bilal Syed, Jianqiang Zhu (Linköping University, IFM, Nanostructured Materials, Sweden); Grzegorz Greczynski (Linköping University, IFM, Thin Film Physics Division, Sweden); Szilárd Kolozsvári, Peter Polcik (Plansee Composite Materials GmbH, Germany); Greger Håkansson (Ionbond, Sweden); Lars Johnson, Mats Ahlgren (Sandvik Coromant, Sweden); Mats Johansson (Seco Tools AB, Sweden); Magnus Odén (Linköping University, IFM, Nanostructured Materials, Sweden)

Ti-Al-N coatings are widely used as hard coatings on cutting tools. One of the proven effective techniques to grow these coatings is cathodic arc evaporation. In cathodic arc evaporation the cathode material is transformed into plasma at a localized spot on the cathode surface. The dynamics of such cathode spot are affected by multiple factors including cathode material, surface roughness, applied magnetic field, surrounding gas, and the grain size etc.

In this study we explore the surface evolution of powder metallurgically prepared Ti0.5Al0.5–cathodes of different grain sizes and their influence on the TiAlN coatings synthesis. The results show that when circular (63 mm diameter) cathodes with 10 and 80 µm grain size are compared after being arced in a N2 ambience (using otherwise identical deposition conditions of a Sulzer/Metaplas MZR-323deposition system), the depth of the affected zone in both cases is about 6 µm. It also contain the same intermetallic phases, independent of grain size. However, when the cathodes are arced in an Ar ambience, this depth is increased to 20 µm for the 10 µm grain size cathode and to 200 µm for the 80 µm grain size cathode. Also here, the affected layer display the same phases for both cathodes. Using these cathodes, TiAlN coatings were deposited on WCo substrates, which were positioned in such a fashion that they cover an angular range of 0o–50o from the surface normal of the cathodes. Coatings grown by the 80 µm grain size cathode show higher macroparticle density and lower coating thickness than the coatings grown by the 10 µm grain size cathode.

The composition of the coatings deposited from the 10 µm grain size cathode were stoichiometric for substrates placed within the angular range of 0o–45o, i.e. Ti0.5Al0.5N1,while beyond 45o it becomes N-enriched. In the case of coatings grown from the 80 µm grain size cathode more aluminum was found in the coating over the entire angular range. Here N-abundance was detected beyond 30o.

4:10 PM B4-1-9 Systematic Investigation of X2BC Phases
Hamid Bolvardi, Mirjam Arndt (Oerlikon Balzers, Oerlikon Surface Solutions AG, Liechtenstein); Jens Emmerlich (RWTH Aachen University, Germany (Until September 2011)); Stanislav Mráz, Denis Music (RWTH Aachen University, Germany); Moritz to Baben (RWTH Aachen University, Germany (Until January 2016)); Konda Gokuldoss Pradeep (RWTH Aachen University, Germany); Helmut Rudigier (Oerlikon Balzers, Oerlikon Surface Solutions AG, Liechtenstein); Jochen Schneider (RWTH Aachen University, Germany)

Mo2BC has been shown to exhibit an unusual combination of very high stiffness (460 GPa) and moderate ductility based on density functional theory data [1]. The ab initio calculated positive Cauchy pressure of Mo2BC [1] and the bulk to shear modulus ratio (B/G) over 1.75 [1] predict an intrinsic ductile behavior [2, 3]. This has been verified via growing Mo2BC thin films and subsequent characterization, where a very good agreement was observed between quantum mechanically generated results and measured values [1]. Recently, utilizing high-power impulse magnetron sputtering (HiPIMS), crystalline Mo2BC was deposited at 380 °C [4], which is significantly lower than a first reported required temperature of 900 °C by direct current magnetron sputtering (DCMS) [1]. Plasma characterizations have been made to reveal the underlying physical mechanisms responsible for this low temperature growth [4]. The reduced synthesis temperature greatly expands the range of technologically interesting substrate materials for application. Subsequently, electronic structure and mechanical properties of X2BC phases with different transition metals were studied using ab initio calculations to investigate other promising candidates [5]. Further attempts have been made to synthesis and characterize a new ternary phase from X2BC family.

[1] J. Emmerlich, D. Music, M. Braun, P. Fayek, F. Munnik, J.M. Schneider, Journal of Physics D-Applied Physics 42 (2009) 185406.

[2] S.F. Pugh, Philosophical Magazine 45 (1954) 823.

[3] D.G. Pettifor, Materials Science and Technology 8 (1992) 345.

[4] H. Bolvardi, J. Emmerlich, S. Mráz, M. Arndt, H. Rudigier, J.M. Schneider, Thin Solid Films 542 (2013) 5.

[5] H. Bolvardi, J. Emmerlich, M. to Baben, D. Music, J. von Appen, R. Dronskowski, J.M. Schneider, Journal of Physics: Condensed Matter 25 (2013) 045501.

4:30 PM B4-1-10 Tribological Behavior of MoBCN Coatings Synthesized by Ion Beam Enhanced Deposition
Xiaodong Zhu (Xi’an Jiaotong University, China); Chen Shang, Longshi Qiu (Xi'an Jiaotong University, China); Guangyu He (Air Force Engineering University, China); Kewei Xu (Xi’an Jiaotong University, China)

Molybdenum nitride coating has low coefficient of friction in comparison to other nitride of transition metals, yet its wear resistance decreases dramatically at elevated temperature. In the present study, MoBCN coatings were synthesized by ion beam enhanced magnetron sputtering deposition from a Mo/B4C composite target. The hardness of MoBCN coating increased with the increase of B content, and the wear resistance could be improved. The wear tests at elevated temperature demonstrated that its wear rate could be reduced to 1/20 of the MoN coating. The fiction coefficient of MoBCN coating was much lower than that of MoN coating. After annealed in atmosphere, the thickness of the oxide layer of MoBCN coating was only about 1/6 of MoN coating, and large amount of oxygen deficient phases such as Mo8O23 and Mo4O11 were found. In contrast, the only oxide phase in the annealed MoN coating was MoO3. This revealed that the introduction of B decreased the oxidation rate of MoN. Since the formation MoO3 phase with low strength and high coefficient of friction was suspended, the coefficient of friction as well as the wear loss of MoBCN coating were reduced. Therefore, doping of B is an appropriate way to solve the problem of low wear resistance of MoN coating at elevated temperatures.

4:50 PM B4-1-11 The Effect of Pulse Bias Voltage on the Temperature Dependent Structural Stability of TiN Coatings Produced via Cathodic Arc Method
Golnaz Taghavi Pourian Azar, Sinan Akkaya, Mustafa Urgen (Istanbul Technical University, Turkey)

Annealing heat treatment of TiN coatings have been the subject of many investigations which have resulted in the stress annihilation, and reduction of internal stresses and hardness of coatings. In our previous studies we have observed that by using high voltage pulse bias it is possible to change preferred orientation, grain size and tribological properties of TiN coatings. In this study, we aim to investigate the role of preferred orientation on temperature dependent structural stability of TiN coatings that are produced by using DC and pulse bias. For this purpose, TiN films were prepared by means of the cathodic arc method on high-speed steel substrates, using DC and pulse bias voltages. Vacuum annealing heat treatment was performed at different temperatures on the as-deposited coatings, to annihilate the stress. XRD structural investigations and nano-indentation hardness measurements were performed on all as-deposited and heat treated samples. According to the results, changes in the preferred orientation from (111) to (220) that is induced by pulse bias application also resulted in less sensitivity to heat treatment cycles.

5:10 PM B4-1-12 Gas Flow Ratio and RF Input Power Effects on Characteristics and Protective Behavior of Sputtering TaN Multilayer Film
Ya-Huei Yang, Fan-Bean Wu (National United University, Taiwan, Republic of China)

In present study, Tantalum nitride, TaN, coatings with crystalline, amorphous, and multilayer microstructure features were fabricated and investigated. The microstructure for TaN coatings was modulated through the adjustments on Ar/N2 gas flow ratio andRF input power. With Ar/N2 gas flow ratio control from 18/2 to 12/8, the TaN films possessed a crystalline to an amorphous feature, respectively. The grain size for crystalline TaN single layer coatings decreased from 36.8 to 30.1 nm with input powers, leading to an elevated mechanical properties. The smaller grain size with more grain boundaries of TaN film fabricated under high Ar/N2 ratio and input power slowed down the corrosion rate. For amorphous TaN coatings deposited at Ar/N2 = 12/8, there was no significant phase transformation when RF input power changed from 75 to 150W. With combination of appropriate parameter regulation for crystalline and amorphous TaN layers, the TaN multilayer coatings were then manufactured for optimization of protective behavior. Hardness, elastic modulus, and tribological characteristics of the TaN multilayer film were discussed in terms of layer modulation.

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