ICMCTF2016 Session F4-1: Functional Oxide and Oxynitride Coatings

Wednesday, April 27, 2016 8:00 AM in Room Royal Palm 1-3
Wednesday Morning

Time Period WeM Sessions | Abstract Timeline | Topic F Sessions | Time Periods | Topics | ICMCTF2016 Schedule

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8:00 AM Invited F4-1-1 PVD Nitride/Oxide Multilayers as Protective Coatings in Milling
Joern Kohlscheen, Christian Bareiss (Kennametal, Germany)
As industrial manufacturing is constantly improving efficiency, advanced cutting tools with superior properties are needed. A major step in this direction was the introduction of thin hard coatings on cutting materials. Today, nitride thin films like TiAlN deposited by means of PVD processes represent the state-of-the-art and have enabled dry and high speed machining. However, limitations of pure nitride coatings are encountered for example in milling of difficult-to-cut materials like super-alloys or when going to even higher cutting speeds. Oxides can outperform nitrides as they are inherently more resistant to oxidation and chip adhesion. As in CVD, alumina has become the material of choice to optimize film properties. The current PVD solution featuring a wear resistant AlTiN base layer and a thinner alumina top layer is presented. The effect of applying a multi-layer structure near the surface is discussed. We start from considerations of the compound properties like hardness, friction coefficient and oxidation resistance. The benefits for tool protection which lead to extension of tool life were evaluated in indexable milling of stainless steel and in some cases also cast iron. The resulting wear patterns will be discussed. An outlook to possible future developments in PVD for cutting tool protection will be given.
8:40 AM F4-1-3 Influence of Varying Nitrogen Partial Pressures on Microstructure, Mechanical and Optical Properties of Sputtered TiAlON Coatings
Nina Schalk, Thierry Simonet Fotso (Montanuniversität Leoben, Austria); Georg Jakopic, Alexander Fian (JOANNEUM RESEARCH Forschungsgesellschaft mbH, Austria); Velislava Terziyska, Rostislav Daniel, Christian Mitterer (Montanuniversität Leoben, Austria)
In the recent years, TiAlON coatings have gained increasing interest owing to their excellent mechanical properties, chemical stability and tunable optical properties. Within this work, a series of TiAlON coatings was grown on Si substrates from powder metallurgical TiAl targets with an Al/Ti atomic ratio of 60/40 by magnetron sputter deposition applying constant oxygen and increasing nitrogen partial pressures. Using energy dispersive X-ray spectroscopy oxygen concentrations between 33 and 60 at.% were detected, while nitrogen contents of only up to 9 at.% could be found. With increasing nitrogen partial pressure, the (Al+Ti)/(O+N) ratio decreased from 2.06 to 0.60. All coatings exhibited a dominating fcc-(Ti1-xAlx)ν(O1-yNy)ξ structure with additional fractions of amorphous oxides as determined by X-ray diffraction and complementary X-ray photoelectron and Raman spectroscopy. The structure of the coatings was further corroborated by transmission electron microscopy, electron energy loss spectroscopy and selected area diffraction. In addition, information about the mechanical and optical properties was gained by nanoindentation and spectroscopic ellipsometry, respectively. The highest hardness could be determined for the coating with an (Al+Ti)/(O+N) ratio of 0.82. With increasing oxygen content, the refraction index and extinction coefficient decreased, but the behavior of the optical properties remained metallic-like. Summarizing, in the current work TiAlON coatings were synthesized exclusively with the fcc-structure irrespective of the oxygen/nitrogen content, with hardness increasing up to 23 GPa and having metallic-like behavior of the refraction index and extinction coefficient.
9:00 AM F4-1-4 The Influence of Oxygen on the Phase Formation at the Al70Cr30 Target Surface and the Synthesized Coatings in Cathodic Arc Evaporation
Max Döbeli (ETH Zurich, Switzerland); Alex Dommann, Xavier Maeder, Antonia Neels (Empa, Switzerland); Jürgen Ramm (Oerlikon Balzers, Oerlikon Surface Solutions AG, Liechtenstein); Helmut Rudigier (Oerlikon Balzers, Oerlikon Surface Solutions AG, Switzerland); Beno Widrig (Oerlikon Balzers, Oerlikon Surface Solutions AG, Liechtenstein)
The surface of powder metallurgical fabricated targets is modified during evaporation by the cathodic arc. The formation of new phases can be understood qualitatively with the help of the phase diagram assuming a locally confined fast evaporation-quenching process. For the synthesis of oxide coatings, oxygen is added to the cathodic arc discharge. The oxygen is not only incorporated in the synthesized coating but can also change the phases and phase composition at the target surface. This was investigated in detail for Al70Cr30 targets. The evaporation rate in function of oxygen flow was measured. Based on this, the atomic ratio of metal to oxygen atoms could be fixed in the deposition process. For the whole range between pure metallic vapour and oxygen saturation, the oxygen flow was increased in small steps and the phase composition at the target surface was compared with those in the synthesized coatings. Some relationship between target surface and coating could be identified and it was possible to create single phase Al8Cr5 target surfaces by the arc operation. It could also be shown that besides the oxygen flow, the particle size and an additional activation of the oxygen in the plasma influence the phase formation at the target surface and in the coating. This knowledge helps to synthesize starting from Al90Cr10 targets α-(Al,Cr)2O3 solid solutions coatings with exceptional high Al content.
9:20 AM F4-1-5 The Influence of Fe-doping on Mechanical Properties and Thermal Stability of Arc Evaporated Al-Cr-O Coatings
Christian Koller, Helmut Riedl, Matthias Bartosik (TU Wien, Austria); Jürgen Ramm (Oerlikon Balzers, Oerlikon Surface Solutions AG, Liechtenstein); Szilárd Kolozsvári (Plansee Composite Materials GmbH, Germany); Paul Mayrhofer (TU Wien, Austria)

The low temperature synthesis of single phase α-Al2O3 coatings by physical vapour deposition has been subject of intense research activities in recent years. Among various technological advancements and coating concepts aiming a controlled oxide phase formation, the alloying with Cr is of particular interest as it facilitates the formation of an (Al,Cr)2O3 solid solution in the desired corundum structure. This material demonstrates comparable mechanical properties as, e.g., chemical vapour deposited Alumina. However, while for Al/Cr-ratios smaller than 2 the single phase corundum structure can be realised, the oxide coatings with smaller Cr-contents still exhibit additional metastable phases, which bears the risk of thermally-induced phase transformations– representing a distinctive loss of the coating’s efficiency for protective applications. Recently, the effect of Fe-doping on the phase formation of cathodic arc evaporated (Al,Cr)2O3 films was investigated and it was demonstrated that the addition of up to 5 at.% Fe distinctively increases the hexagonal phase fraction [1]. Here, we address the question whether these microstructural modifications also result in an enhancement of mechanical properties (indentation modulus and hardness), and how the latter scale with the Fe concentration within the coatings and deposition parameters applied. In order to examine the thermal stability of the (Al,Cr,Fe)2O3 solid solution vacuum and ambient air annealing up to 1100 °C is carried out. Results are discussed and compared with (Al,Cr)2O3 films.

[1] Koller et al. Scripta Materialia 2015 (97) 49–52

9:40 AM F4-1-6 Aluminum Oxynitride Thin Films Deposited by Reactive Closed Field Direct Current Magnetron Sputtering
Maria Fischer, Mathis Trant, Kerstin Thorwarth, HansJosef Hug, Jörg Patscheider (Empa, Laboratory for Nanoscale Materials Science, Switzerland)

The introduction of oxygen (O) into thin films of aluminum nitride (AlN) allows for a wide range of variability in physical parameters of this transparent, hard and noncorrosive material. The already broad application field of AlN can even be expanded by aluminum oxynitride (AlON), e.g. in terms of oxidation resistant protection layers due to the inherent O content in the films.

AlON was deposited as approximately 1 μm thin films by magnetically unbalanced reactive closed field direct current magnetron sputtering (R-CFDCMS). Different O contents were established by changing the O/N ratio in the reactive gas administered to the process. O was found to incorporate into the AlN wurtzite crystallites in the form of a solid solution up to 8 at%. The resulting films were under tensile stress and experienced lattice shrinkage caused by Al vacancies and grain refinement related to enhanced renucleation rate. Increasing O insertion lead the ternary material system gradually from O-doped AlN towards N-doped aluminum oxide (Al2O3), hereby inducing considerable changes in crystallinity, optical refraction and residual stress state. In the regime of 8-16 at% O an intergranular amorphous Al2O3 matrix enveloped the AlON crystallites, reducing the tensile stress and allowing for hydrogen (H) incorporation. The threshold of 16 at% O represented the onset of compressively stressed and thus H free films consisting mainly of an X-ray amorphous AlON network in which O-N interactions were discovered. The elucidation of the different film regimes helps to reproducibly deposit films with desired physical qualities tied to the intrinsic O content and opens the way to the practical application of AlON thin films.

10:00 AM F4-1-7 Exploration of Various Properties for Chromium Oxide-Nitride Coatings Prepared by Reactive Sputtering
Divyeshkumar Dave (Charotar Univ. of Sci. and Tech. (CHARUSAT) and Dr.Jivraj Mehta Inst. Of Tech., India); Kamlesh Chauhan, Sushant Rawal (Charotar University of Science and Technology (CHARUSAT), India)

The aim of this study is to identify the formation of chromium oxide-nitride films by reactive sputtering of chromium target using oxygen and nitrogen as reactive gases along with helium that was used as an inert gas. The objective was to explore the consequence of temperature and nitrogen flow rate variation on formation of chromium oxide-nitride films. The identification of respective oxide/nitride phases of chromium was done by X-ray diffraction. The contact angle and surface energy of the deposited films were studied using contact angle measuring system. Initially at lower deposition temperature of 200ºC, the deposited films are amorphous and hydrophilic. When temperature is increased from 200ºC to 600ºC, the formation of crystalline films is observed and its behavior gets transformed from hydrophilic to hydrophobic. Tribological properties of chromium oxide-nitride films are examined in different testing conditions. Tribological properties of these films are dependent on variation of temperature and nitrogen flow rate.

10:20 AM F4-1-8 Influence of Multilayer Arrangement on Structure and Mechanical Properties of Arc Evaporated Oxide, Nitride, and Oxide/Nitride Coatings within the Systems Al-Cr-N and Al-Cr-O
Robert Raab (TU Wien, Austria); Szilárd Kolozsvári (Plansee Composite Materials GmbH, Germany); Richard Rachbauer (Oerlikon Balzers, Oerlikon Surface Solutions AG, Liechtenstein); Paul Mayrhofer (TU Wien, Austria)

Cathodic arc evaporation, being an extremely successful and widely used physical vapour deposition (PVD) technology, features high flexibility for the preparation of protective coating systems. Aluminium-chromium-based oxides and nitrides, for instance, are typically applied to cutting and forming tools, or milling devices, owing to their outstanding thermo-mechanical properties, wear and oxidation resistance, representing crucial capabilities for such forming and machining tools.

Another major benefit of cathodic arc evaporation is the possibility to significantly influence the coating microstructure by the adaption of deposition parameters, which allows for enhanced and specifically tailored properties.

In this regard, we have studied the architectural design and resulting mechanical properties of Al-Cr-based oxide, nitride, and oxide/nitride coatings. Therefore, AlxCr1-xN and (AlxCr1-x)2O3 multilayers as well as mixtures thereof were synthesised by reactive arc evaporation using powder metallurgically prepared Al0.7Cr0.3 targets. By careful adjustment of deposition time and reactive gas configuration, the individual (AlxCr1-x)2O3, AlxCr1-xN, and multilayers could be designed with different bilayer periods and interfaces. Scanning electron microscopy (SEM) analyses revealed the influence of the deposition time per layer to the architectural structure and surface topology. By reducing the time per layer during the deposition (thus increasing the total number of layers), the (AlxCr1-x)2O3 and AlxCr1-xN layers have different thicknesses, resulting in a decreased bilayer period, decreasing roughness and an increasing hardness. According to TEM and XRD results the Al-Cr-based multi-layered coatings indicate a single phase face centred cubic (fcc) structure with a preferred (200) and (220) orientation. With decreasing layer thickness, we observe a slight shift of the diffraction peaks to higher 2ϴ angles, which suggests reduced compressive stress formation. Evaluation of the full width at half maximum, based on the B1-like cubic (200) XRD peak, reveals a lower grain size for coatings with lower deposition time per layer.

Based on our results we can conclude that arc evaporation and the knowledge-based reactive gas flow control and arrangement leads to AlxCr1-xN/(AlxCr1-x)2O3 multilayers with excellent hardnesses and moderate surface rouhgnesses, when the bilayer period is optimized.

10:40 AM F4-1-9 Self-healing Mechanisms in Niobium Based Oxides
Jingjing Gu, Dylan Steiner, JonErik Mogonye, Thomas Scharf, Samir Aouadi (University of North Texas, USA)

We seek to gain new insights into the fundamental deformation mechanisms of self-healing oxides in response to thermal and/or mechanical stimuli. Model systems that will be investigated are binary oxides that are at least partially restored through the extrinsic or intrinsic addition of silver or silver oxide nanoscale elemental inclusions that form ternary oxides (e.g., Nb2O5 + Ag à AgNbO3).The selected oxides were produced in bulk (sintering) and in thin film (unbalanced magnetron sputtering) form. A surface crack was created and a healing agent was added intrinsically or extrinsically. The sample was annealed to stimulate the self-healing process by forming a ternary oxide in the crack region. X-ray diffraction was used to explore phase evolution, chemical compositions, and structural properties of the sintered and sputtered samples before and after annealing. SEM equipped with EDS were used to investigate the chemical and morphological properties of the fracture surface. Mechanical testing techniques were also applied to estimate the self-healing properties and performance.

Time Period WeM Sessions | Abstract Timeline | Topic F Sessions | Time Periods | Topics | ICMCTF2016 Schedule