ICMCTF2014 Session F4: New Oxynitride and Oxide-based Coatings
Wednesday, April 30, 2014 1:50 PM in Room Royal Palm 4-6
F4-2 Effect of Oxygen Incorporation on the Structure and Elasticity of Ti-Al-N-O Coatings Synthesized by Cathodic Arc and High Power Pulsed Magnetron Sputtering
Marcus Hans, Moritz to Baben, Denis Music, J. Ebenhöch (RWTH Aachen University, Germany); Daniel Primetzhofer (Uppsala University, Sweden); Denis Kurapov (Oerlikon Balzers Coating AG, Liechtenstein); Mirjam Arndt, Helmut Rudigier (OC Oerlikon Balzers AG, Liechtenstein); Jochen Schneider (RWTH Aachen University, Germany)
Ti-Al-N-O coatings were synthesized by cathodic arc and high power pulsed magnetron sputtering. The effect of substituting nitrogen by oxygen on structure and mechanical properties was investigated. The chemical composition of the coatings was determined by means of elastic recoil detection analysis and energy dispersive X-ray spectroscopy. Lattice parameters and Young‘s moduli were obtained by X-ray strain analysis and nanoindentation, respectively. Both, the decrease of lattice parameter and Young’s modulus with increasing oxygen content can readily be understood based on ab initio calculations: The substitution of nitrogen by oxygen is enabled by formation of metal vacancies, preserving thereby charge neutrality.
F4-3 Magnetron Sputtering of p-type AgFeO2 Thin Films with the Delafossite Structure Using a Combinatorial Approach
Ulf Jansson, Fang Mao, Tomas Nyberg, Thomas Thersleff (Uppsala University, Sweden)
Delafossites AMO2 (A= Cu,Ag, Pd, Pt; M=Fe, Co, Ni, Cr, Al, Mn, etc) have interesting potential applications as transparent p-type conducting oxides, photocatalysts, luminescent materials, batteries and thermoelectric materials. Recently, high temperature superconductivity was also suggested for doped members of this type of oxide compounds. The delafossites can be described as natural nanolaminates with MO2 layers separated by A planes. The chemical stability of these compounds is defined by the linear O-A-O bonds. Copper-based delafossites have been synthesized using solid-state reactions, hydrothermal synthesis methods, sol-gel methods and, in a few cases, reactive sputtering with high temperature post-annealing (≥700oC). Very few studies, however, have previously been published on silver-based delafossite films deposited by sputtering. The main challenge is that the silver-based delafossites are easy to decompose at high temperatures (>400oC) due to the less stable O-Ag-O bonds. Furthermore, the synthesis of Ag-based delafossites by reactive sputtering is usually restricted to a narrow parameter window.
In this work, we have deposited delafossite AgFeO2 thin films with reactive magnetron sputtering using a combinatorial approach with gradient films. Rapid screening combined with XRD, XPS and XRF were used to determine the chemical composition and phase composition. The most interesting films were studied by TEM. Optical and electrical properties have also been investigated. Our results show that the AgFeO2 successfully can be deposited without post-annealing using a pulsed Ag target. The process window is very narrow and strongly dependent on deposition temperature, sputtering power, pulse frequency, O2 flow rate, working pressure, etc. An optimum temperature is 400 oC and a pulsing frequency of 150 kHz. The XRD and TEM showed that the AgFeO2 films were textured with the (00l) planes perpendicular to the growth direction also on an amorphous SiOx substrate. A very strong substrate dependence was observed with good quality films on Si and a poor crystallinity on glass. Furthermore, the films were p-type and transparent. Further post-annealing in air improved the electric properties.
F4-4 Influence of Si Doping on Process Stability and Coating Properties During Arc Deposition of (Al, Cr)2O3
Ludvig Landälv (Linköping University, IFM, Thin Film Physics Division and Sandvik Coromant R&D, Sweden); Emmanuelle Göthelid, Mats Ahlgren (Sandvik Coromant R&D, Sweden); Lars Hultman, Björn Alling, Per Eklund (Linköping University, IFM, Thin Film Physics Division, Sweden)
α-Al2O3 made by PVD-processes has been a long sought goal in coating development for the cutting tool industry. Different approaches have been taken throughout the years, such as alloying with materials stabilizing the corundum phase, i.e. Cr, as reported in [1, 2, 3]. Having achieved α-(Cr, Al)2O3 phase from compound targets, there are still many problems to solve with respect to process stability and coating quality. The reactive arcing of mixed AlCr targets in oxygen creates a large amount of droplets as well as target poisoning , which leads to a reduced film quality and uneconomical use of target material, especially on an industrial scale. A recent discovery shows that Si can be added to the AlCr-material in order to stabilize the process, creating a more even erosion of the cathode . However, the Si-content in the target need to be balanced carefully in the light of another study indicating that Si in the coating stabilizes the cubic phase instead of the desired corundum phase . It remains to be found with which Si content the improved erosion of the targets may result in better film integrity, that is, fewer droplet and voids while retaining hardness, E-modulus, crystal structure, and improving the machining properties of the original AlCr oxide.
Thus, this work aims to study the influence of adding different amounts of Si to AlCr-target material with increasing Al/Cr ratio respect to erosion rate of the target as well as the resulting coating properties. SEM, XRD, TEM, and XPS among other techniques showed that some Si is incorporated into the coating when having 10 at% Si in the target with Al/Cr=1. The α-(Cr, Al)2O3 coating, free from silicon, change phase to possibly cubic-(Cr, Al)2O3 upon incorporating silicon. The hardness is also reduced when adding Si in the coating. The questions of where the silicon is incorporated in the coating is also further investigated in this work.
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F4-5 Synthesis-structure-property Relations of Al-oxide-based Coatings
Jörg Paulitsch, Christian Koller (Vienna University of Technology, Austria); Richard Rachbauer, Jürgen Ramm (Oerlikon Balzers Coating AG, Liechtenstein); Peter Polcik (PLANSEE Composite Materials GmbH, Germany); David Holec (Montanuniversität Leoben, Austria); Paul Heinz Mayrhofer (Vienna University of Technology, Austria)
Many investigations already indicated that alloying Al to ceramic-like nitride coatings, such as CrN or TiN, increase their mechanical and thermal properties. Especially the formation of dense alumina (Al2O3) outer layers during high temperature oxidations is highly acknowledged due to its chemical inertness and passivating character. However, synthesizing crystalline corundum-type alumina itself indicated to be challenging, especially when using deposition temperatures <700°C.
Within this study we present results on selected alloying materials, obtained from first principle calculations, which not only influence the crystallographic appearance of Al-Cr-O coatings but also enhance the target evaporation characteristic during cathodic arc evaporation, hence the process itself. Furthermore architectural optimized Al-O-based multilayer coatings were deposited using low and high ionizing deposition techniques, like conventional direct current magnetron sputtering or cathodic arc evaporation, respectively, to indicate the possibility of stabilizing preferential crystallographic configurations by tailoring the bi-layer thickness.Our results demonstrate the advantages of a combined computational and experimental investigation as well as of a sophisticated layer arrangement to deposit high performance coatings.
F4-7 Structure and Electronic Properties of AlCrOxN1−x Thin Films Deposited by Reactive Magnetron Sputtering
Hossein Najafi, Ayat Karimi (EPFL, Switzerland); Marcus Morstein (PLATIT AG, Switzerland)
Metal oxynitride thin films, a novel class of mixed anionic solid structures, have gained an intense interest during recent years related to the unique interplay of oxygen (O) and nitrogen (N) with metals in the material structure. In this regard, we studied the structure and electronic properties of Cr-rich oxynitrides (Cr/Al~1) showing a cubic (B1) structure in the nitride regime, O/(O+N) < 0.6. The obtained films in this growth regime exhibited a well-developed columnar structure and high nanohardness values ranging from 30 to 33 GPa. Our results show the incorporation of oxygen into the films without any oxide region segregation results in the development of a strong (002) crystallographic preferred orientation and a decrease of the cubic lattice parameter, which allows to suggest the formation of a substitutional AlCr(OxN1-x) solid solution. Material system electronically behaves like nitrides; however, the higher charge transfer between metals and oxygen, as compared to less electronegative nitrogen, favors the formation of an iono-covalent solid structure. In the range of oxygen content from 0.6 < O/(O+N) < 0.97, transition regime, coatings with diffuse columnar structure and high values of metal vacancies were formed. However, the cubic lattice survives despite the large proportion of oxygen. According to the structural and electronic properties of corresponding layers, we assign this region to the formation of metastable monoxides with B1 structure, which are stabilized by the presence of a high amount of vacancies. The nanohardness decreased to about 21-25 GPa as a consequence of the formation of vacancies and changes in chemical bonding states as well as in the coating microstructure. Coatings in the oxide regime with nitrogen contents close to or even below the detection limit of chemical composition analysis, O/(O+N)>0.97, consisted of a solid solution of (Al,Cr)2(O0.97,N0.03)3 with corundum lattice and finer columnar structure. It was verified that the incorporation of even small amounts of N in the corundum lattice results in the development of hard coatings with proper wear resistance and less brittle nature.
F4-8 Stoichiometry Gap in MF Sputtered CrON Thin Films
Marco Renzelli, Marco Sebastiani, Edoardo Bemporad (University of Rome "Roma Tre", Italy); Herbert Kappl, Martin Fenker (FEM Forschungsinstitut Edelmetalle & Metallchemie, Germany)
Oxynitrides of transition metals are an important scientific and technological topic. Some of them exhibit tunable properties according to the O/N ratio, but not all the metals can form them, and their properties are dependent on the growing conditions, if prepared as thin films. The authors found a lack of knowledge in the literature on the production of CrON by medium frequency (MF) magnetron sputtering, so this is a report on the synthesis and characterization of MF sputtered CrON thin films on silicon and M2 high speed steel substrates. Temperature control was employed, together with substrate biasing to influence the coatings microstructure. X-ray diffraction (XRD) and glow discharge optical emission spectroscopy (GDOS) analysis point to a stoichiometry gap between an oxygen doped CrN-like film and a nitrogen doped CrOx one. Frequency and duty cycle variation of the DC pulses on the chromium target shifted the oxygen flow threshold between the two compositions. Polarization tests for corrosion test, stress measurements and instrumented micro and nanoindentation were employed to fully characterize the coatings produced.
F4-9 Influence of the Power Supplied in the Optical Properties of ZrOxNy/ZrO2
José Alfonso, Manuel Pinzón, Jhon Olaya, Gloria Cubillos (Universidad Nacional de Colombia Bogotá, Colombia)
The zirconium oxynitride has physical-chemistry properties that allow be used in different applications such as a temperature sensor device, as a corrosion resistance coating and recently, ZrOxNy thin films have been proposed for decorative and biological applications. For these reasons, we study the influence of power supplied to the target on the structure, in the morphology and optical properties of ZrOxNy/ZrO2 thin films deposited on common glass using RF reactive sputtering technique, in atmosphere of N2/O2, with a flow ratio ΦN2/ΦO2 of 1,25. Structural analysis was carried out through X-ray diffraction (XRD); morphological analysis was done through scanning electron microscopy (SEM) and the optical response was evaluated through transmittance measurements. DRX analysis show that the ZrOxNy/ZrO2 films were grown with monoclinic crystalline structures and preferentially oriented along the (-111) plane. The SEM analysis, evidence that the films grew with homogeneous morphology and exhibit a columnar growth, and used the transmittance values and through Swanepoel method we calculated the refractive index, thickness and absorption coefficient of the crystalline films, additionally the energy gap was determined used the Urbach's formula.
F4-10 Influence of the Annealing in the Corrosion Resistance of BixTiyOz Coatings Deposited on Ti6Al4V
Manuel Pinzón, José Alfonso, Jhon Olaya (Universidad Nacional de Colombia Bogotá, Colombia)
The ferroelectric and optical properties of family of compounds bismuth titanate (BixTiyOz) have been focus of many researches, of which have generated applications as opto-acoustic devices, photocatalytic activity in degradation of several compounds and non-volatile ferroelectric memories, inter alia. Nevertheless, the studies of other properties of this compounds as eg its behavior in corrosive environments or its use as protective layer against attack by degrading agents, have been very few. Taking in account this situation, and based in before works made for us, which show that these compounds in amorphous phase are potentially useful as protective layer against corrosion, we propose in this work, evaluate the effect of crystalline evolution of bismuth titanate by means annealing to several temperatures, on its corrosion resistance. For this purpose, bismuth titanate thin films were grown on titanium alloy (Ti6Al4V) substrates, through RF magnetron sputtering. In order to observe the evolution the crystallinity of the coatings, these were submitted to an annealing at temperatures in the range among 298 K and 973 K in step of 100 K, The structure crystalline were characterized by X-ray diffraction (XRD) and the corrosion resistance of the coatings was studied by Potentiodynamic polarization test (Tafel extrapolation). The coatings annealed, revealed a change in its microstructure, since they evolve from a completely amorphous phase to a polycrystalline phase. The preliminary results shows that the corrosion resistance of the coating is much better in the amorphous phases of bismuth titanate than in the polycrystalline phases, this is probably due to that low temperatures favors the formation of passive TiO2 films over the substrate and reinforced the protective of the bismuth titanate coating, while to high temperatures the passive TiO2 film is reduced.
F4-11 Characterization of Microstructure and Basic Properties of Plasma Sprayed Oxides Coatings Modified by Submicrocrystalline Powders of Different Oxides
Grzegorz Moskal (Silesian University of Technology, Poland); Szyman Polis (SUT, Poland)
Microstructural characterization and basic properties description of atmospheric plasma spraying oxide coatings modified by nano- and submicro-crystalinne different types of oxides will be presented in this article. In first part the short characterization of nano- and submicro-crystalinne oxides powders will by showed, especially theirs characterization form grain size and phases composition point of view. Analyzed powders were as follow: RE2O3 (RE=Sm, Eu, La), ZrO2, 3YSZ, Y2O3, CeO, α-Al2O3 and γ-Al2O3. Those powders will by described by STEM, XRD and laser diffractions methods. In second part of investigations microstructural characterization of APS coatings of 8YSZ, Al2O3 and Al2O3 x 13 TiO2 with addition of nano- and submicro-crystalinne oxides powders will be showed. The morphology of the coatings will be described, their hardness and results of erosion tests in different conditions. The value of KIc parameters will be estimated as well.
Financial support of Structural Funds in the Operational Program - Innovative Economy (IE OP) financed from the European Regional Development Fund - Project No POIG.0101.02-00-015/09 is gratefully acknowledge.