ICMCTF2011 Session B5-1: Hard and Multifunctional Nano-Structured Coatings

Thursday, May 5, 2011 8:00 AM in Room Golden West

Thursday Morning

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8:00 AM B5-1-1 Structure and Properties of Ti-Al-Y-N Coatings Deposited from Filtered Vacuum-Arc Plasma
Vitaliy Belous, Volodymyr Vasyliev (Kharkov Institute of Physics and Technology, Ukraine); Volodymyr Goltvyanytsya, Sergiy Goltvyanytsya (Real Ltd., Ukraine); Elena Reshetnyak, Volodymyr Strelnitskij, Galina Tolmacheva, Alexandr Luchaninov (Kharkov Institute of Physics and Technology, Ukraine); Oksana Danylina (Krivoy Rog Technical University, Ukraine)

It is known that nanostructured multi-component nitrides like Ti-Al-Y-N may have a unique combination of properties: high hardness, wear resistance, thermal stability and oxidation resistance, which may allow using them as protection coatings on tools and machine parts, working under extreme conditions. Deposition of coatings from filtered vacuum arc plasma leads to additional quality improvement due to formation of more uniform structure and reduction in the surface roughness. In this paper the effect of the amplitude of the pulse substrate bias and percentage of yttrium on structure and properties of Ti-Al-Y-N vacuum-arc coatings, deposited from filtered vacuum arc plasma, were studied.

The coatings were produced in vacuum-arc system with a straight magnetic-electric filter by sputtering of as-cast TiAlY cathodes with the following deposition on the steel substrates at a nitrogen pressure of 0.1 Pa and pulse substrate bias amplitude of 0.5-2.5 kV. The deposition rate reached 14-16 μm/h, the coating thickness was of 6-8 μm. Scanning electron microscopy and atomic force microscopy (AFM) were used for investigation of the structure and surface morphology of the coatings. The elemental composition of the coatings was controlled using X-ray fluorescence analysis. Hardness was measured by nanoindentation. Oxidation resistance tests were performed using the thermal analyzer.

Elemental percentage of Ti, Al, Y in the coatings and cathodes were in a good mutual accordance. At the same time, the coatings were of uniform thickness and homogeneous composition. SEM of the surface samples showed the high quality filtering of the plasma flow, because only few defects on the films surface were observed. Samples cross section showed that the coating Ti-Al-N had a columnar structure like traditional vacuum-arc nitride coatings deposited at a constant substrate bias. Yttrium additions to the cathodes caused the changes in the coatings structure: with increasing of Y content in cathodes from 0 to 2.5 wt.%, columnar film structure became considerably less expressed. In this case, significant surface morphology changes were observed. In the AFM 3D images the surface of the films deposited at pulse bias of 1.5 kV amplitude was characterized by cellular-like microrelief with the cell size of about several hundred nanometers with hardness H=35-40 GPa.

According to the results of the thermogravimetric analysis, all produced Ti-Al-Y-N coatings possess sufficiently high oxidation resistance. The most oxidation-resistant coatings were deposited at pulse bias amplitude of 1.0-1.5 kV and contained of 1.0-2.5 wt. % of Y.

8:20 AM B5-1-2 Growth of Hard Amorphous Ti-Al-Si-N Thin Films
Hanna Fager, Amie Fallqvist, Naureen Ghafoor (Linköping University, Sweden); Mats Johansson (Seco Tools AB Fagersta, Sweden); Per Persson, Magnus Odén, Lars Hultman (Linköping University, Sweden)
We propose amorphous transition metal nitrides with a preferred covalent bonding for a next class of tough materials with tuneable hardness. (Ti,Al)1-xSixN (0.10≤x≤0.27) thin films were grown onto Si (001) and cemented carbide substrates by cathodic arc evaporation of Al-rich Ti-Al-Si cathodes in an Ar-N2 gas mixture. The as-deposited films were analyzed by elastic recoil detection analysis (ERDA), x-ray diffraction (XRD), nanoindentation, and transmission electron microscopy (TEM). With an incorporation of 19 at.% Si, the film structure changes from microcrystalline to nanocrystalline. With further incorporation of Si (27 at.%), the films assume an x-ray and electron amorphous state. The hardness of amorphous films is as high as 14 GPa. A comparison with magnetron sputtered amorphous Ti-Al-Si-N films will also be reported.
8:40 AM B5-1-3 Solid Solutions and nanostructures in Al(Si)N Hard Coatings
Joerg Patscheider (Empa, Switzerland)
Nitride-based coatings with specific nanostructures such as multilayers with nanoscale dimensions and fully phase-separated nanocomposites are in the focus of scientific interest since two decades. The deposition of transition metal nitrides and silicon leads to the formation of bi- and multiphase coatings containing silicon nitride. Depending on the materials system and preparation conditions, such coatings may show enhanced hardness and other favorable properties. These make such coatings not only a subject of intense research, but are the reason for their application potential as protective coatings on a wide variety of tools and components. Using aluminum instead of transition metals causes the formation of optically transparent Al(Si)N coatings that show, despite enhanced hardness of more than 30 GPa, some interesting differences with respect to transition metal nitride/silicon nitride coatings. A solubility limit exists for silicon contents around 6 atomic %, that seemingly is thermodynamically stable. Correspondingly, the Al-Si-N system forms, as a function of the silicon content, either solid solutions or a two-phase nanocomposite structure. Structural investiga-tions lead to a growth zone model that accounts for the different nanostructures. Investigations on model systems using nanoscale multilayers show that in this materials system the absence of a major hardness enhancement, characteristic e.g. for TiN/Si3N4, can be understood in terms of epitaxy and elastic properties of the single phase components. The addition of oxygen to form Al(Si)N1-xOx causes, similar to silicon addition, grain refinement and a gradual disappearance of the columnar structure with increasing oxygen content. Despite very high oxygen concentrations up to 20 at% O hardness values of 25 Gpa are reached. The properties of these coatings will be presented and underlying mechanisms will be discussed.
9:20 AM B5-1-6 Corrosion Resistance and Hardness of Nb-Si-N Coatings Deposited by Dual Magnetron Sputtering
Giovanni Ramírez, Sandra Rodil, Stephen Muhl, Lazaro Huerta (Universidad Nacional Autonoma de Mexico); Enrique Camps, Luis Escobar-Alarcón (Instituto Nacional de Investigaciones Nucleares, Mexico)
In this work, we prepared thin films of Nb-Si-N using two separate magnetrons, where one target was Si and the other Nb. The atmosphere was a variable mixture of argon and nitrogen. The film composition and structure was modified by varying the power of the two magnetrons independently. For the Si target, the rf source was varied between 40-200 W and for the Nb target, we tested dc powers between 100-300 W. The aim of the study was to find deposition conditions that lead to a dense hard microstructure presenting both high hardness and corrosion resistance, in a similar fashion as the nc-TiN/a-SiNx phases reported by different authors. The films were characterized by X-ray photoelectron spectroscopy to obtain the composition and the chemical bonding characteristics. Similarly, Raman spectroscopy was used to identify the bonding characteristics and the presence of isolated silicon phases. The corrosion resistance was evaluated for films deposited on two different steels using dc and ac electrochemical techniques. The dc techniques include potentyodynamic polarization and polarization resistance, data that were analyzed using the Tafel method. Meanwhile, electrochemical impedance spectroscopy as a function of the immersion time up to 72 hours was used to evaluate the stability of the coatings and electronic equivalent circuits were used to model the variations of the coatings parameters in time. The results of the different characterization techniques were correlated to the deposition conditions and the films composition.
9:40 AM B5-1-7 Quaternary-Phase Coatings in the Cr-WC-N System
Michael Walock (University of Alabama, Birmingham); Issam Rahil (Arts et Metiers ParisTech, France); Yujiao Zou (University of Alabama, Birmingham); Corinne Nouveau (Arts et Metiers ParisTech, France); Andrei Stanishevsky (University of Alabama, Birmingham)
Binary tungsten carbide films can be smooth, hard crystalline materials, but with low fracture toughness. Tungsten nitride films are frequently harder, but are more brittle. Chromium nitride films have excellent wear and oxidation resistance, but often develop a porous columnar structure with low hardness. The composites of these binary compounds offer a possibility to tailor the material for a desired combination of properties. However, little is known about ternary and quaternary thin-film systems based on these compounds. To this end, we have used reactive RF-magnetron sputtering with Cr and WC targets to form ternary and quaternary thin-film coatings (film thicknesses from 1 to 2 microns), with an argon/ nitrogen working gas. The films were deposited onto Si, Ti, CoCr, WC, and high-speed steel substrates at a substrate temperature below 500 K. The structural and mechanical properties of the resulting coatings have been characterized with XRD, XPS, AFM, SEM/ EDX, and nanoindentation. Depending on the deposition conditions, the XRD, XPS, and EDX results indicate the presence of the binary (W2C and WC1-x), ternary (WC-N and Cr-WC), and quaternary (Cr-WC-N) phases. Our SEM and AFM results show smooth films for the tertiary and quaternary compounds. The mixed binary phase W2C and WC1-x films demonstrated nanoindentation hardness above 40 GPa, but they partially delaminated from the majority of the substrates. All ternary compositions (WC-N and WC-Cr systems) tested to date have shown strong adhesion to the substrates, but the hardness was in the range of 12 – 20 GPa. However, the hardness values for some films with Cr-WC-N composition (Cr/W ratio ranges from 1.4 to 2.8:1) were measured in excess of 35 GPa. The formation of a nanocrystalline (grain size 5-8 nm) nanocomposite (i.e. more than one pure phase present) material was suggested on the basis XRD and XPS data. These results combined with low roughness (RMS 1.1 – 1.5 nm) and high adhesion make these quaternary thin-film coatings a promising material for demanding applications such as cutting tools, friction pairs, and intermediate layers for deposition of micro- and nanocrystalline diamond coatings.

This work has been supported by the U.S. National Science Foundation (DMR-0806521, DMR-0922910) and the Regional Council of Burgundy, France.

10:00 AM B5-1-8 Self-Organized ZrN/Si3N4 Lamellar Growth During Reactive Dual Magnetron Sputtering of Zr1-xSixNy Thin Films at High Temperature
Naureen Ghafoor, KuNai- Yuan, Jens Birch, Jens Jensen, Lars Hultman, Magnus Odén (Linköping University, Sweden); Jian-Guo Wen (University of Illinois at Urbana- Champaign); Ivan Petrov (University of Illinois at Urbana-Champaign)

In the field of superhard nanocomposites the research has focus on introducing new multifunctional materials as well as on the understandings of the structural complexity of the nanocomposites which boost their functionality, such as hardness, thermal stability, and corrosion resistance. Here we present an experimental study on Zr1-xSixNy (0 ≤ x ≤1; 1 ≤ y ≤ 1.22) alloys synthesized by reactive magnetron sputter deposition onto single-crystal MgO(001) and Al2O3(0001) substrates at 800°C that allows for phase separation during growth and hence make possible to design the structure of the internal interfaces by controlling the composition. For this high temperature, epitaxial growth allows incorporation of as much as 10 at.% of Si in ZrN, which enhances oxidation resistance and thermal stability of the films up to 1000°C, while retaining its superhard nature. The structure of Zr0.8Si0.2N films constitutes 3-5 nm thick lamellas that extend in the growth direction with a strong (002) texture. It is revealed by lattice resolved z-contrast transmission electron microscopy imaging that the lamellas consist of ZrN and amorphous Si3N4 separated by a possible crystalline SiNx: Zr tissue phase.

10:20 AM B5-1-9 Modulation Structure and Mechanical Properties of W/ZrB2 Multilayers
G.Q. Liu, Y.B. Kang, De Jun Li, X.Y. Deng (Tianjin Normal University, China)

Nanoscale multilayers made of borides, nitrides, and carbides, exhibiting desired mechanical properties, have been developed and applied to various kinds of industries for the past decades. In this study, we worked with W/ZrB nanoscale multilayers coatings. Tungsten, as a high atomic-number and refractory material, has been widely applied in applications such as wear- or corrosion-resistant components in high-temperature and high-vacuum environments due to its excellent mechanical, thermal and electrical properties. The refractory compound ZrB also has a high hardness, high melting point, high electrical conductivity and excellent corrosion resistance. Because W and ZrB have different crystal structures, we expect little mutual intermixing of both nanolayers at elevated temperatures and hence preserve the high-temperature tribological performance. Several different types of transition metal nitrides, borides, and carbides multilayered coatings, such as W/NbN, Mo/NbN, AlN/VN, AlN/TiN, TiN/TiB2, TiB2/TiC, TiN/SiNx, have been explored. For the W/ZrB2 multilayers addressed in this work, studying the influences of various growth parameters will help us determine their microstructure and the related mechanical properties.

In our previous works (Appl. Phys. Lett. 91 (2007) 251908, Surf. Coat. Technol. 201 (2007) 6812, J. Vac. Sc. Technol. B25 (2007) L11, J. Vac. Sci. Technol. A24 (2006) 966), we have specifically achieved some insight into the relation between the growth parameters and the microstructure and mechanical properties of lots of multilayers such as CrN/ZrN, ZrC/ZrB2, ZrN/TiAlN, ZrN/W2N. Over 30 GPa hardenss with desired fracture resistance has been observed in these multilayer systems. In this work, W/ZrB2 nanoscale multilayers were deposited on silicon by magnetron sputtering at room temperature. The multilayered modulation structure and mechanical properties of the W / ZrB multilayers were studied using SEM, XRD, surface profiler and nanoindenter. The mechanical properties of the multilayers were controlled by modulation periods (Λ) ranging from 9.5 to 40 nm and modulation ratios (tw:tZrB2) from 1:1 to 1:9. All of the multilayers with clear sharp interfaces revealed higher hardness and elastic modulus than the rule-of-mixtures value for monolithic W and ZrB2 coatings. The maximum hardness of 41.5 GPa and critical load of 62.5 mN could be obtained for the multilayer with a Λ of 30 nm and tw:tZrB2 of 1:3 . The polycrystalline and multilayered modulation structures were directly responsible for the enhanced mechanical properties.
10:40 AM B5-1-10 Growth and Properties of Cr2GeC Epitaxial Nanolaminated Thin Films
Per Eklund (Linköping University, Sweden); Matthieu Bugnet, Michel Jaouen, Sylvain Dubois, Christophe Tromas, Thierry Cabioc'h (University of Poitiers, France)

The Mn+1AXn phases (n = 1 – 3, or ‘MAX phases’) are a group of ternary carbides and nitrides (X) of transition metals (M) interleaved with a group 12-16 element (A) [1]. Although a relatively little researched member of the MAX-phase family, Cr2GeC exhibits a number of traits that render it interesting from a fundamental-research point of view, such as its reported thermal expansion coefficient which is the highest of the known MAX phases, and its reported anomalously high density of states at the Fermi level. Because of these intriguing observations and the limited amount of studies available, we are interested in Cr2GeC. For synthesis of this phase, thin-film growth is a potentially important approach because of the relative ease with which numerous MAX phases can be epitaxially grown, often as single crystals. Here, we report growth of epitaxial phase-pure Cr2GeC onto Al2O3(0001) both directly and using a TiN(111) seed layer. The use of a seed layer results in fewer defects as evidenced by the rocking curve full width at half maximum. For optimized composition, phase-pure epitaxial Cr2GeC can be grown at temperatures above 700oC. This enables determination of mechanical and electrical properties. Increased Ge or C content results in film containing additional impurity phases such as Cr5Ge3Cx and pure Ge segregated on the surface. A reduction in temperature yields polycrystalline growth of Cr2GeC in the temperature range 500 – 650oC.

[1] See review: P. Eklund et al Thin Solid Films 518 1851 2010

11:00 AM B5-1-12 In-Situ Characterisation of Microstructure Evolution in Ti1-xAlxN Coatings During Annealing
Christina Wuestefeld, David Rafaja, Volker Klemm, Milan Dopita, Mykhaylo Motylenko (TU Bergakademie Freiberg, Germany); Carsten Baehtz (Forschungszentrum Dresden-Rossendorf, Germany); Claude Michotte (CERATIZIT, Luxembourg); Martin Kathrein (CERATIZIT, Austria)

Hardness and high-temperature stability of hard coatings are indirectly controlled by their microstructure induced by the deposition process, as the initial microstructure strongly affects the kinetics of microstructure changes at elevated temperatures. Thus, the development of the microstructure at elevated temperatures is an important topic for Ti1-xAlxN coatings which can be used in machining applications. In this study, the development of microstructure in Ti1-xAlxN coatings at elevated temperatures was investigated using in-situ synchrotron high temperature glancing angle X-ray diffraction (HT-GAXRD) experiments and related to the original microstructure of the coatings, which was modified via the titanium to aluminium ratio and the bias voltage.

The Ti:Al ratio in the coatings varied between 60:40 and 33:67; the bias voltage ranged from -40 to -120 V. The in-situ synchrotron HT-GAXRD experiments were done at 450°C, 650°C and 850°C. After each annealing step, the coatings were cooled to 100°C and an additional GAXRD measurement was performed in order to seek for the spinodal decomposition of metastable fcc-(Ti,Al)N.

From the analysis of the GAXRD pattern, the phase composition as well as the macroscopic lattice strain and the stress-free lattice parameter of the fcc-(Ti,Al)N phase were determined for all investigated temperatures. At 850°C AlN segregated from fcc-(Ti,Al)N and formed c-AlN and w-AlN. It was found that for the same coating composition the ratio between the individual phases present in the coating after annealing at 850°C was different in the coatings deposited at -40 V, -80 V and ‑120 V. This effect of the initial microstructure, which was adjusted by the bias voltage during CAE deposition, on the phase evolution during annealing will be related to the results from GAXRD and transmission electron microscopy.

11:20 AM B5-1-13 Laminated Structure in the Internal Oxidation of Ta-Ru Coatings
Yung-I Chen, Sin-Min Chen (National Taiwan Ocean University, Taiwan)
During the application of refractory alloy coatings for protective purpose at high temperature under oxygen containing atmospheres, the internal oxidation phenomenon has been observed and explored. The characteristic of the internal oxidation zone is a laminated structure with alternative oxygen-rich and deficient layers stacked with a general orientation. The forming conditions has been proposed, i.e., one of the elements should be relatively noble, the coatings exhibit an orientated columnar structure in the as-deposited state, and the inward diffusion of oxygen is faster than the out-diffusion of the constituents of the coatings. In this study, Ta-Ru coatings were prepared with various rotating speeds of substrate and sputtering powers in the deposition processes, and then annealed at 600oC in a 50 ppm O2-N2 atmosphere. The periods of laminated layers were examined by transmission electron microscopy. We also investigated the surface roughness and mechanical properties for the internally oxidized coatings.
11:40 AM B5-1-11 Nanostructured Superhard Films Ti-Hf-Si-N, their Properties and Structure
Alexander Pogrebnjak (Sumy State University, Ukraine); Vyacheslav Beresnev (Kharkov National University, Ukraine); Piotr Konarski (Tele and Radio Research Institute, Poland); Vladimir Uglov, Fadey Komartov (Belarus State University, Belarus); Mikhail Kaverin (Sumy Institute for Surface Modification, Ukraine); Dmitriy Kolesnikov (Belgorod State University, Russia); Vladimir Grudnitskiy (Kharkov National University, Ukraine); Nemat Makhmudov (Samarkand Branch of Tashkent Institute of Information, Uzbekistan); Maxim Il’yashenko, Grigorii Kirik (Sumy State University, Ukraine)

Using vacuum-arc source with HF discharge, superhard nanocomposite films of 1.05 to 1.2 µm thickness were fabricated. Their thickness depended on the bias potential on the substrates and N pressure in a chamber. It was found that the film hardness was ≥ 42 GPa and elastic modulus was E = 490 ± 10 GPa, nanograin size being 5 to 35nm. It was demonstrated that depending on the substrate bias potential, ratio of α-H5S4, nc-HfSi2 and nc-TiN or (Ti,Hf)N phases changed. Using SIMS, RBS, EDS with SEM analysis, the films stoichiometry and concentration profiles over depth were measured. Analyzing the film cross-section, we found good quality of the films, very good adhesion to the steel 3 substrates, pores and columnar structures were not observed.

XRD and TEM with micro-diffraction were applied to determine sizes of nanograins of the above mentioned phases. 200oC to 600oC annealing in vacuum demonstrated that a hardness increased almost by a factor of 15 to 17% (48 to 52 GPa), i.e. an effect of self-hardening due to a process of spinodal phase segregation along grain interfaces was observed. Annealing at higher than 1100oC temperature resulted in formation of an oxide layer of 120 to 140 nm thickness at the film surface.

The work was funded by the NAS project of Ukraine – Nanosystems, Nanocomposites, and Nanotechniques.

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