Advanced Characterization of Coatings and Thin Films

Friday, May 3, 2013 8:00 AM in Room Royal Palm 1-3

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8:00 AM TS2-2-1 Correlation Between the Rockwell Indentation Test and the Progressive Load Scratch Test for Assessment of Coating Adhesion
Nicholas Randall (CSM Instruments, Switzerland); Reinhold Bethke (Fraunhofer IST, Germany); Gregory Favaro (CSM Instruments, Switzerland)

In recent years it has become current practice to employ a wide range of test methods to assess the adhesive properties of thin films and coatings, ranging from the simple tape-peel test to the more advanced pull-off and 3-point bending tests. Many such methods have high operator subjectivity, high data variability and in many cases are unsuitable for industrial Quality Control (QC) use where assessment is done regularly and often by several operators. The Rockwell indentation test (ISO 26443 and VDI 3198) has become common for evaluating the adhesion of hard coatings deposited on various substrates, but the applied load (1472 N) is often too high causing the 200 µm radius diamond indenter to plunge too deeply into the substrate making it difficult to classify the resultant coating damage around the edges. The progressive load scratch test (ASTM C1624, ISO EN 1071-3, ISO 20502) is now widely used to characterize the adhesion of thin hard coatings with high repeatability. However, a direct correlation between these two methods has never been attempted.

It has been proposed that a smaller radius diamond indenter (possibly 50 µm radius) could be employed with the Rockwell indentation test, using a lower applied load, in order to concentrate the maximum stress nearer to the sample surface causing more focused failure of the coating-substrate interface. The objective of this study is to fabricate samples representative of the 6 failure categories of the standard Rockwell test, to then evaluate the same coatings with lower load and smaller indenter radius, and thirdly to test the same samples with the progressive load scratch test. It is hoped that this could lead to better correlation of data obtained with all such methods and aid industry in better QC control of their coatings.

8:20 AM TS2-2-2 How to Make Tribological Tests Physical
Norbert Schwarzer (Saxonian Institute of Surface Mechancis, Germany)

Caused by the many effects taking place during a general tribological test it is a relatively ambiguous goal to create not just a tribo-model or simulation tool, but to make it fit for inversion and thus, analysis of such tribological tests. The talk features an approach where tribo parameters, like Archard's wear depth parameter kd, are extracted from effective interaction potentials [1], which themselves are built up and fed from more physical-oriented measurements like Nanoindentation and PHYSICAL scratch. By using such effective material potentials one can derive critical loading situations leading to failure (decomposition strength). A subsequent connection of these decomposition or failure states with the corresponding stress or strain distributions allows the development of rather comprehensive tribological parameter models applicable in wear and fatigue simulations as demonstrated in this work.

From this a new global increment wear model has been developed on the basis of the effective indenter concept [1, 2] by using the extended Hertzian approach [3]. The models do not only allow to analyze certain tribological experiments like the well known pin-on disk test or the more recently developed nano-fretting tests, but also to forward simulate such tests and even give hints for better component life-time predictions. Within the talk a few examples will be shown.

[1] N. Schwarzer, Short note on the effect of pressure induced

increase of Young's modulus, Phil. Mag., submitted July 2011

[2] N. Schwarzer, G. M. Pharr: „On the evaluation of stresses during

nanoindentation with sharp indenters”, Thin Solid Films, Vol. 469-470C pp.

194-200

[3] N. Schwarzer, T. Chudoba, G. M. Pharr: „On the evaluation of

stresses for coated materials during nanoindentation with sharp indenters”, Surf. Coat. Technol, Vol 200/14-15 pp 4220-4226

[4] N. Schwarzer: "The extended Hertzian theory and its uses in

analysing indentation experiments", Phil. Mag. 86(33-35) 21 Nov - 11 Dec

2006 5153 – 5767, Special Issue: “Instrumented Indentation Testing in Materials Research and Development”

8:40 AM TS2-2-3 Depth Profiling >40-µm Anodized Coatings Using Glow Discharge Optical Emission Spectroscopy
Fuhe Li, Justin Laiduc, Warren York, Wendy Rivello (Air Liquide Electronics-Balazs NanoAnalysis, US)

Radio Frequency (RF) glow discharge optical emission spectroscopy (GD-OES) has been developed in our laboratory to characterize various coatings and thin films. Thick dielectrics (insulators) such as anodized coatings, typically > 40 µm, are used in semiconductor, coating equipment, defense, aerospace, automotive, architectural, medical, marine, sporting goods, home appliances, and recreation. These thick coatings can be analyzed by RF GD-OES for elemental composition, spatial elemental distribution, and trace impurities. The use of RF plasma for material sputtering, excitation and ionization avoids many intrinsic limitations associated with traditional electron beam, ion beam or x-ray techniques. Deep depth profiling a > 40 µm anodized coating (e.g. Type III hard coatings) throughout its entire thickness down to its substrate at nm depth resolution can only be accomplished by RF GD-OES.

With simultaneous multi-element (40 or more including H, C, N, O, Na, Mg, Al, P, S, Cl, Fe…) profiling capability (real-time profiling), RF GD-OES has been successfully used to examine coating uniformity, interfacial contamination, and surface stoichiometry (<10 nm). The RF GD-OES results demonstrate the usefulness of this technique in optimizing anodization processes, facilitating base material (aluminum alloys) selection, controlling surface and interfacial contamination, and preventing premature failure of an anodized coating or subsequent layer. The signal intensity produced by RF GD-OES has a simple and well-defined mathematical (linear) relationship with elemental concentration in a material. A wide linear dynamic range (over six orders of magnitude) possessed by RF GD-OES coupled with various NIST traceable material standards developed in our laboratory have made accurate surface, interfacial and bulk analyses possible.

9:00 AM TS2-2-4 Mechanical Properties of Nanocrystalline Coatings Revealed by Bending Tests on Fabrication-Unaffected Micro-Cantilevers
Angelika Riedl (Materials Center Leoben Forschung GmbH, Austria); Rostislav Daniel (Montanuniversität Leoben, Austria); Mario Stefenelli (Materials Center Leoben Forschung GmbH, Austria); Thomas Schöberl, Otmar Kolednik, Christian Mitterer, Jozef Keckes (Montanuniversität Leoben, Austria)

Thin nanocrystalline coatings featuring outstanding mechanical properties have gained much interest in recent years. The application of deposition techniques operating far from the thermodynamic equilibrium results in the formation of pronounced depth inhomogeneities in microstructure and strain over coating thickness compared to their bulk counterparts. Thus, instead of surface sensitive parameters obtained using indentation techniques, knowledge about their mechanical behaviour is required in order to assess the relationship between process conditions, thickness-dependent coating properties and functional behaviour. The presented approach is a step forward in the characterization of thickness-averaged mechanical properties of crystalline coatings at the micrometer scale. It consists of an etching step of the substrate to isolate the coating without affecting its interface to surface inhomogeneity, thus preserving its nucleation zone. Afterwards, a rectangular cantilever is fabricated by cutting the free-standing coating with a focused gallium ion beam. The cantilever beam is loaded by an indenter, where load-displacement curves are recorded until fracture. Then, the fracture surfaces are evaluated by scanning electron microscopy. Using this approach, the fracture mechanism can be identified and linked to coating microstructure and residual stress state. The influence of deposition parameters, annealing treatments and coating architectures on the fracture properties of representative CrN and TiAlN coatings will be demonstrated. The approach allows the identification of mechanisms, which are responsible for the deterioration of the coating performance and which are often not well understood or remain unrevealed by other characterization techniques.

9:20 AM TS2-2-5 Cyclic and Monotonic Mechanical Properties of Micro Samples Acquired with Custom Built Setups Working up to 1000 Hz – CuAl10Ni5Fe4, 3Y-PZT
Tobias Kennerknecht (Fraunhofer Institute for Mechanics of Materials, IWM, Germany); Sandy Pelletier, Thomas Straub (Karlsruhe Institute of Technology, Germany); Chris Eberl (Fraunhofer Institute for Mechanics of Materials, IWM, Germany)
Testing micro samples, thin films or coatings requires novel techniques and special equipment with a maximum flexibility to adjust for the samples. Thus, several piezo driven custom built setups were developed in our group, in order to investigate micro samples and thin films loaded in uniaxial tension, compression, bending or subjected to a multiaxial stress state. Most of these setups are designed for cyclic experiments and work in resonance, allowing for fatigue tests at frequencies up to 1000 Hz. Thus, very high cycle fatigue experiments (more than 1E8 cycles) can be performed in a reasonable amount of time. Furthermore, monotonic tests are available, using a setup, which can realize frequencies from 0 to 100 Hz. The present paper will give an overview on experiments conducted with the latter setup (low frequency setup, LFS) as well as with a resonant uniaxial tension-compression-setup (resonant setup, RS) working at frequencies up to 2 kHz. In addition, damage- and microstructural analyses will be addressed, which were established using electron microscopy and a focused ion beam, in order to reveal failure mechanisms. The investigated materials treated in this paper are aluminum bronze (CuAl10Ni5Fe, cross section 260 μm x 130 μm) and 3Y-TZP (Yttria stabilized zirconia, dimensions: 200 x 200 x 1200 μm3), which were manufactured using specially developed micro casting processes (KIT, Karlsruhe), and which are comparable to free standing thin films. Both setups are excited by means of a piezo. Data is acquired by means of a field programmable gate array, which enables parallel acquisition of 8 analog channels at sample rates up to 200 kHz and partial on board treatment of the data. In the LFS, a camera with microscope is used for optical strain measurement performed with digital image correlation. Load is measured using a dynamic load cell. The travel range of the piezo is enlarged by means of a linear stage. The setup can be adapted for flat dog bone tensile samples as well as for three point bending tests. In the RS, the piezo actuator carrying the sample is aligned in direction of gravity. A mass is attached at the free end of the sample, and the system is excited sinusoidally at its natural push-pull frequency. The displacement of the freely hanging mass is measured using a capacitive sensor. Thus, the inertial load of the mass acting as the applied cyclic load on the sample can be determined. The results will help understanding the active fatigue mechanisms and damage formation of micro molded aluminum bronze and of 3Y-TZP. We greatly acknowledge the German Science Foundation (DFG) for sponsoring this work.
9:40 AM TS2-2-6 High Cycle Fatigue of Al and Cu Thin Films by a Novel High-Throughput Method
Sofie Burger, Chris Eberl (Karlsruhe Institute of Technology, Germany); Alexander Siegel, Alfred Ludwig (Ruhr University of Bochum, Germany); Oliver Kraft (Karlsruhe Institute of Technology, Germany)
Mechanical properties and fatigue lifetime of thin films differ significantly from those of bulk materials. With decreasing film thickness the fatigue failure changes from a dislocation based mechanism to pore formation and grain boundary cracking. To obtain a better understanding of the governing mechanisms, a new fatigue setup for micro cantilever bending was developed. A micro-machined Si cantilever coated with Al or Cu thin films is excited at its resonance frequency by a piezo actuator. The thin film undergoes cycles of different strain amplitudes along the cantilever from a maximum near the shoulder to zero at the free end. With a reflected laser beam from the surface the bending amplitude as well as the reflectivity is detected. Thus, by observing the damage front on the thin film after a certain number of cycles, it is possible to compile a fatigue lifetime diagram from one cantilever. Experimental results of cycled thin films of sputter deposited Al, Cu, and Cu with a Ti seed layer will be presented. The micro- and damage structure of these samples was qualitatively and quantitatively analyzed by a SEM/FIB Dual Beam. The results will be discussed in the light of current models for fatigue in thin films. Furthermore, a growth law based description for damage formation induced by fatigue will be presented.
10:00 AM TS2-2-7 Structural, Morphological and Mechanical Characterization of Mo Sputtered Coatings
SilviaMaria Deambrosis, Enrico Miorin, Monica Fabrizio (CNR, Italy); Marco Sebastiani, Edoardo Bemporad (University "Roma Tre" Rome, Italy)
The use of Molybdenum is of interest in various technological areas. Because of its remarkable properties (high melting point (2610°C), high conductivity, good chemical stability and high hardness), Mo coatings have been used in microelectronics (gates for MOS integrated circuits, interconnections, and diffusion barriers), as back contacts for solar cells and they are suitable candidates to fabricate superconducting microcalorimeters for high-performance radiation detectors. Moreover Molybdenum films are used in nuclear energy applications and for missile and aircraft parts. As a consequence of their appeal, a variety of deposition techniques and conditions has been employed to obtain Mo coatings.Nonetheless, a detailed study of the process-structure-properties for Mo-based coatings is still lacking in the literature.In this work, we present an investigation, based on the use of high resolution characterization methodologies, on the properties of Mo deposited by sputtering on titanium substrates. Different films have been grown under different sputtering conditions to find a correlation between a variety of deposition parameters and the intrinsic properties of the films. The working gas has been also changed (Ar, Xe, etc.) to evaluate its influence on the growing layer. Microstructural characterization activities consisted of scanning electron microscopy (SEM), X-ray diffraction (XRD) and focused ion beam (FIB) cross section analysis. The residual stress distribution was investigated by using an innovative high resolution focused ion beam micro-ring-core method. The nano-mechanical properties of the films (hardness and modulus) were analyzed by nanoindentation testing. Wear resistance and adhesion were finally analyzed by means of scratch and tribological tests, using a fully-computerized UMT tester. Results showed a significant modification of coatings’ microstructure, depending on the adopted working gas and process parameters. In particular, a transition from a micro-crystalline columnar microstructure to a nano-porous microstructure was observed by using different kind of working gas. Modifications of the residual stress field and mechanical properties were also observed, as a function of the process parameters, and a correlation with observed adhesion and wear resistance is proposed.
10:20 AM TS2-2-8 Effect of AlN Layer on the Growth and on the Structure of Reactive Sputtered TiAlN Thin Films and Multilayers
Antonella Rizzo, Daniele Valerini, Luciana Mirenghi, Roberto Terzi, Leander Tapfer (ENEA, Italy); Renato Giannoccaro, Umberto Galietti (Politecnico di Bari, DIMEG, Italy)
Machining of aerospace materials is one of the major challenges of modern manufacturing. It has been assessed that nano-multilayered PVD coatings applied at tooling of cemented carbide are useful for a significant tool life improvement in hard conditions of the cutting machine such as in the case of superalloys nichel-based (Incone l 718) and of the alloys titanium-based (TiAl6V4). In particular, TiAlN/AlN multilayers are attracting great interest for the possibility to modulate their mechanical and tribological properties through the multilayer design. In this work TiAlN single layer, TiAlN/AlN gradient structure and TiAlN/AlN nano-multilayers were prepared using a reactive magnetron sputtering system equipped with TiAl and Al targets. The aim of this work is to investigate how the multilayer design affects the thermal and tribological properties of the coatings. The chemical composition has been carried out by XPS analyses. The thermal stability has been characterized by X-ray diffraction, calorimetry and thermogravity while the mechanical properties have been investigated by wear tests.In the as deposited sample the main peak has been deconvoluted into two components c-AlN and c-TiAlN, confirming the template function of the cubic phase of AlN film. c-AlN reflection increases as expected up to 700 °C, disappears at 1000 °C to arise in hexagonal phase. c-TiN reflection comes out at 700 °C to increase at increasing annealing temperature. c-TiAlN reflection at 700 °C is narrower (indicating a higher structural order due to a recovery process) and also shifted on the left (indicating the presence of structural stress due to the decomposition process highlighted by c-TiN presence). The sliding tests carried out at 30 °C indicated a wear rate of about 5x105 mm3/N/m for all coatings which have been observed. At 400 °C the single-layer coating presents a wear rate of the same order of magnitude as those tested at room temperature. The TiAlN/AlN coating with a gradient structure has a chemical composition of Ti 19 %, Al 36 %, N 43 %. The multilayered coated samples decreased their wear rate by one order of magnitude reaching their optimum in the sample of TiAlN/AlN nano-structured with a chemical composition of Ti 23 Al 40 %, N 37 %. A ll multilayered coatings exhibit an onset of the pronounced exothermic peak due to oxidation at ≥900 °C, hence, at least ~400 °C above that for c-TiN.
10:40 AM TS2-2-9 Structural Characterization of Amorphous GdTM2 (TM=Fe, Ni and Co) from First-principles
Raquel Lizarraga, Erik Holmstrom (Universidad Austral de Chile, Chile)
We performed a structural characterization of amorphous GdTM2 (TM=Fe, Ni, and Co) metallic glasses. An efficient and computationally inexpensive method based on Density Functional theory is used to obtain amorphous structures of the glasses. In our analysis we calculate radial distribution functions, angle distribution functions as well as bond lengths and average coordination numbers. The coordination number for the Gd-Gd pairs increases in the series a-GdNi2, a-GdCo2 and a-GdFe2, whereas the TM-Gd pair coordination number decreases is that order. This is in excellent agreement with the experimental data from the anomalous x-ray scattering method.
11:00 AM TS2-2-10 Influence of Stoichiometry and Architecture on Mechanical Properties of Cathodic Arc Deposited Ti-Al-Cr-N Coatings
SaiPramod Pemmasani (International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), India); RaviChandra Gundakaram (International Advanced Research Centre for Powder Metallurgy and New Materials(ARCI), India); KoteswararaoV. Rajulapati (University of Hyderabad, India); Ramakrishna Mantripragada, Suresh Koppoju, Krishna Valleti, ShrikantV Joshi (International Advanced Research Centre for Powder Metallurgy and New Materials(ARCI), India)

Titanium and Chromium based nitrides find widespread applications as wear resistant coatings on cutting and forming tools. There have been continuous efforts to enhance their performance through various means, including designing their architecture in the form of nanocrystalline, nanocomposite or multilayer coatings. The mechanical properties of these coatings are significantly influenced by the crystal structure, microstructure and composition of the coating. Consequently, there exists an opportunity to control the coating performance by either tailoring the composition, through addition of alloying elements to achieve different stoichiometry, or the microstructure, through introduction of multilayers and nanosized grains. In the case of multilayer coatings, deposition of alternate layers with varying modulus is known to enhance crack resistance and, in turn, the toughness of the coating.

In the present study, Ti-Al-Cr-N based coatings were deposited by cathodic arc evaporation in monolayer and multilayer configurations on tool material substrates. The Al and Cr percentage in the coatings was varied in the range 0-65% by suitably manipulating the process parameters and four different compositions were comprehensively investigated. XRD analysis was carried out to ascertain the crystal structure while microstructural characterization was carried out by FIB-SEM and TEM to observe the variation in grain structure on the surface and cross section of the coatings. Stresses were measured employing an X-ray residual stress analyzer. Mechanical characterization was done using nanoindentation to determine the hardness and modulus, and scratch testing to assess adhesion. In situ scanning probe microscopy was also used to map the mechanical properties of the multilayer coatings. The hardness and modulus of the coatings were found to vary with Al and Cr percentage and correlated with the plasticity, toughness and residual stresses present in the coatings. Results suggest that there exists a critical Al content at which a maximum in hardness is obtained. Furthermore, the variation in sub-surface deformation during scratch testing and toughness with changing composition, and due to the multilayer configuration in the coating, was studied. Mapping of modulus variation between different layers of the multilayer coatings revealed that a substantial modulus mismatch existed between alternate layers that could lead to enhanced toughness. The implications of this study in enabling identification of a suitable coating composition and architecture to yield properties desirable for industrial applications will also be discussed.

11:20 AM TS2-2-11 Fabrication and Characterization of Polymethylmethacrylate (PMMA) Thin Film by Plasma Polymerization
Chuan Li (National Central University, Taiwan, Republic of China); Jang-Hsing Hsieh (Ming Chi University of Technology, Taiwan, Republic of China); Yuan Hung Lin (National Central University, Taiwan)
Poly×methyl×methacrylate (PMMA), also called acrylic glass, is transparent, chemically stable, thermoplastic and inexpensive, making it suitable for many biochemical applications. Among different fabrication processes of PMMA such as gelation, injection and casting, plasma polymerization is the one capable of depositing nano scale films on almost any substrate uniformly and rapidly. In this study, we investigated the structure, composition, surface and mechanical properties of deposited PMMA films on glass by RF power plasma inside a vacuum chamber. The deposition was carried out under different RF power, working pressure and deposition time, from which an optimal fabrication condition was explored. On the characterization part, following tests were carefully conducted: the thickness (around 20 to 160nm) was estimated by surface profiler; microstructures was determined by Fourier transform infrared spectroscopy (FT-IR); surface chemical compositions were examined by X-ray photoelectron spectroscopy (XPS); surface morphology, roughness and mechanical stiffness were measured by atomic force microscopy (AFM) and the wettability by water contact angle. Primary results showed that deposited films are physically and chemically stable for more than a week, which are readily available for cell culture, anti-microbial tests, drugs or proteins release and other bioengineering applications.