Papers

ICMCTF2006 Session B7-3: Properties and Characterization of Hard Coatings and Surfaces

Tuesday, May 2, 2006 8:30 AM in Room Golden West

Tuesday Morning

Start	Invited?	Item
8:30 AM		B7-3-1 Formation of Ternary Nitride Thin Films by Magnetron Sputtering Co-Deposition: Solid Solution and Composite Materials C.S. Sandu, R. Sanjines, M. Benkahoul, F. Medjani, F. Levy (EPFL, Switzerland) Thin films of M-X-N (M stands for early transition metal and X = Si, Ge, Sn) are studied as protective coatings. Ti-Si-N, Ti-Ge-N, Ti-Sn-N, Nb-Si-N, Zr-Si-N and Cr-Si-N single layer thin films have been deposited by reactive magnetron sputtering at constant temperature Ts = 240°C, from confocal targets in a mixed Ar/N₂ atmosphere. The chemical reactivity of germanium and tin with nitrogen is significantly lower than that of Si and Ti. In this, the Ti-Ge-N and Ti-Sn-N systems are different from Ti-Si-N. Typical changes in the morphology and structure of M-X-N films are induced by X addition. Nanocrystalline composite films are formed in all these investigated ternary systems. The increase of the X content in the films is related to the decrease of the size D of the MN crystallites following approximately the relationship CX ~1/D. We propose a model for the film formation of M-X-N ternary compound deposited by DC magnetron sputtering. Three distinct composition ranges are pointed out: 1- the solubility range: single phase MN:X film is deposited, 2- the range of formation of the coverage layer: MN:X crystallites are coated with a layer of XNy material, 3- the range of reduction of the crystallite size: increasing the surface to volume ratio of the MN nanocrystallites. In the case of Nb-Si-N and Zr-Si-N systems, Si atoms can substitute metal atoms in the cubic MN lattice up to a critical concentration (CSi ~ 4 at.%). Ti-Si-N and Ti-Ge-N systems are different: no solubility of Si and Ge in the TiN lattice is observed. The resistivity measured as a function of temperature reveals abrupt variation of the temperature coefficient of resistivity as a function of X concentration. It is proposed to provide experimental mean for determining the limit of X solubility in M-X-N ternary systems and for following the thickness evolution of the XNy coverage layer in the composite films.
9:10 AM		B7-3-3 Interface Growth Morphologies in Pulsed Laser Deposited, Room Temperature Grown Multilayer Hard Coatings W. Waldhauser, J.M. Lackner (Joanneum Research Forschungsgesellschaft GmbH, Austria); L. Major, B. Major (Polish Academy of Sciences, Poland) The mechanical behaviour of multilayer coatings is strongly influenced by the type of the formed interfaces between the different layers. On the one hand, hardness and elasticity of the multilayer coating depend partly on the crystal structures, textures and lattice distortion caused by the repeated re-nucleation due to the chemical change at the interface; on the other hand, coating failure is shifted to higher loading by crack deflection at these interfaces. Multilayer coatings grown by high-energetic deposition techniques always struggle with atomic mixing of both adjacent coating materials due to high energetic ion implantation, preventing the growth of sharp interfaces. One of these high-energetic deposition techniques is the Pulsed Laser Deposition (PLD) technique, characterized by pulsed and within the pulse alternating high- and low-energetic particle fractions, hitting successively the substrate surface. Such deposition conditions were shown to be highly advantageous for low temperature deposition by the densification of the growth structures due to activated diffusion and re-sputtering, but increases the difficulty in depositing multilayer structures. The current paper addresses these specific growth conditions based on Ti/TiN and Cr/CrN multilayer coatings. High resolution transmission electron microscopy results were performed to understand the nucleation and growth of these materials. Texture analyses in the separate layers show high influences of the underlain layer. A decrease of the particle energy during depositing resulted in more distinct interfaces and - by the comparison to adhesion strength results from scratch testing - allows conclusions for choosing adequate deposition parameters for very dense room-temperature grown multilayer coatings with sharp interfaces.
9:30 AM		B7-3-4 Increase in Micro-Hardness of (Ti,Cr,Al,Si)N Films by Thermal Annealing at 1000°C H.E Ezura, K.I Ichijo (Keio University, Japan); H. Hasegawa (Okayama University, Japan); K. Yamamoto (Kobe Steel Ltd, Japan); A. Hotta, T. Suzuki (Keio University, Japan) Ceramic coatings have been widely used to improve the performance of cutting tools as well as to extend the lifetime of the tools especially in such hard conditions as high-speed and dry cuttings. Thermal stability of the films, therefore, is one of the key parameters for cutting tools, being less damaged even at elevated temperature while cutting. In this paper, thermal stability of quintary (Ti,Cr,Al,Si)N films are investigated. In recent reports, embedding Si into metastable nitride films improved the mechanical and chemical properties of ceramic films. Here the (Ti,Cr,Al,Si)N films were deposited by cathodic arc ion plating method, using Ti-Cr-Al-Si alloy source. The films were characterized by X-ray diffraction measurement (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and micro-hardness measurement. The lattice parameter, crystal structure and micro-hardness of the films were evaluated as a function of (Al+Si) contents. As the (Al+Si) content increased from 0.55 to 0.77, it was found that the micro-structures of the films change from cubic to hexagonal, allowing decrease in micro-hardness from 31 to 26 GPa. Several thermal treatments were carried out changing temperatures around 900°C in vacuum below 10^-3 Pa for 2 hours. We will present the increasing micro-hardness of the quintary films even at very high temperature reaching 1000°C.
9:50 AM		B7-3-5 Some Nano-Scale Correlations Between Structure and Properties in PEO Alumina Films R. Khan, A.L. Yerokhin, A. Pilkington, A. Leyland, A. Matthews (The University of Sheffield, United Kingdom) Plasma Electrolytic Oxidation (PEO) of aluminium can be used to form surface films, consisting predominantly of alpha and gamma alumina, at near to ambient bulk substrate temperatures. This is attributed to the effect of surface microdischarges which provide high rates of heating and cooling at the surface. Such highly transient surface conditions are favourable for the formation of coatings with ultra fine-grained and amorphous structures, possessing enhanced mechanical properties. The purpose of this work was to investigate some correlations between structural features, hardness and elastic modulus, which are developed within the coating material at a nano scale. The crystalline alumina coatings were produced on aluminium substrates using a pulsed current PEO technique in which pulse duty cycle and frequency were varied, providing different coating growth rates and heat fluxes to the surface. Structural studies were carried out using XRD, SEM, EDX and TEM methods whereas mechanical properties were evaluated using nanoindentation techniques. It is demonstrated that, in terms of H/E ratio, the resilience characteristics of the alumina coatings formed under the conditions of pulsed current PEO approach those of advanced a-DLC and Me-DLC films.
10:10 AM		B7-3-6 Effect of Depth Profile of Residual Stress on Milling Performance of TiAlN Coated Inserts H. Fukui (Tool Materials Development Group, Japan); S. Imamura (Sumitomo Electric Hardmetal Corp., Japan); K. Yamaguchi, J. Iihara (Sumitomo Electric Industries, Ltd., Japan) This study was intended to investigate the effect of the depth profile of residual stress on milling performance of TiAlN coated inserts. This residual stress has a large impact on the milling performance; however there has been no study that has attempted to clarify the relationship between the depth profiles of residual stress. The depth profiles of residual stress were carried out by an adjustment of the substrate bias voltage. In this work, the TiAlN films were deposited at the fixed substrate bias voltage of -50V, and linearly gradient substrate bias voltage from -50V up to -150V, on a WC-Co substrate by using the cathodic arc ion plating method. The depth profiles of residual stress measurement were carried out by using the sin² ψ method with maintaining the X-ray incident angle at beam-line BL16XU of the SPring-8 in Japan. At a fixed substrate bias, the compressive residual stress was 0.5 GPa constant from a substrate to a surface of the film. On the other hand, at linearly gradient substrate biases, the compressive residual stress was increased to a maximum value of 5.5 GPa gradually from a substrate to a surface of the film. The milling performances of TiAlN coated inserts were conducted at AISI 1049 as a work material. In particular, the insert of linearly gradient substrate biases enhanced the fracturing property of the cutting edge compared to that of the fixed substrate bias in this test. The fracturing property has a close connection with the maximum value of compressive residual stress on the top of the film.
10:30 AM		B7-3-7 Oxidation Resistance Properties of Al-Ti-Si-N Coatings Prepared by the Cathodic Arc Ion Plating Method for High Speed Cutting Applications K. Sato, A. Kondo, Y. Tanaka (Mitsubishi Materials Corporation, Japan); Y. Onishi, N. Ichimiya (Mitsubishi Matarials Kobe Tools Corporation, Japan) Al-Ti-Si-N coatings were deposited on WC-Co and platinum substrates by using the cathodic arc ion plating method. Oxidation resistance properties of these films were investigated by using X-ray diffraction (XRD), Transmission electron microscopy (TEM) and X-ray photoelectron spectrometer (XPS). Addition of Si to Al-Ti-N coatings improved the oxidation resistance and Al-Ti-Si-N coatings with higher Si content composition displayed higher oxidation resistance at elevated temperatures in air. Structure and composition evolution of the local area of the Al-Ti-Si-N films were also investigated at elevated temperatures and the results were discussed with the oxidation resistance property. Al-Ti-Si-N coated carbide endmills were evaluated and offered significantly better performance in the machining of hardened steels with the high cutting speeds. Wear mechanism and cutting characteristics were discussed with the film properties.
10:50 AM		B7-3-8 Oxidation and Wear Behaviors of Ti-Based Thin Films J.H. Hsieh (Ming-Chi University of Technology, Taiwan); A.L.K. Tan, X.T. Zeng (Singapore Institute of Manufacturing Technology, Singapore) The degradation of Ti-based coatings is known to be due to the formation of titanium oxide (TiO₂) on their surfaces. In this study, wear and thermal oxidation behaviors of various magnetron sputtered Ti-based thin films were studied using Raman spectroscopy after static oxidation and sliding wear. The oxidized surfaces after the static oxidation and the wear debris generated from pin-on-disc wear test with alumina ball were characterized using Raman spectroscopy to identify the compounds, especially oxides, to gain a better understanding of the tribochemical reactions. In this study, wear and oxidation behaviors of TiN, TiCN (N rich), TiCN (C rich) , TiAlN (Ti rich), AlTiN (Al rich), TiSiN and TiCNO thin films were characterized using Raman Spectroscopy, Scanning Electron Microscopy, and X ray diffractometer. It is found that AlTiN and TiSiN have the lowest oxidation rates while TiCN has the lowest friction coefficient.
11:10 AM		B7-3-10 Corrosion Behaviour of MoS₂-Based Coatings Deposited onto High Speed Steel by Reactive Magnetron Sputtering M. Fenker, H. Kappl, A. Savan (FEM, Germany) MoS₂-based films were deposited using magnetron sputtering from a pure target. Doping was accomplished by "co-deposition" from separate targets onto substrates having 2-fold rotation. An additional experiment had also a Cr⁺ ion etch for surface preparation, followed by a Cr adhesion layer, made using a Cr target mounted on a cathodic arc evaporation source. MoS₂ and Al- and Ti-doped MoS₂ coatings have been deposited onto high speed steel (HSS) and glass substrates for corrosion investigations. The coatings were characterised by scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction measurements. The corrosion behaviour of the samples was electrochemically measured by open-circuit-potential (OCP) measurements and by potentiodynamic corrosion tests in 0.8 M NaCl solution (pH 7). Additional the MoS₂-based coatings on HSS have been exposed to a salt spray test (according to DIN 50021). The corrosion investigations revealed that the addition of Al and Ti to MoS₂ shifts the open-circuit-potential for about 60 to 80 V to lower values, i.e. the dopants make the MoS₂ coating a little bit less noble. In OCP tests a strong activity was found for MoS₂- and Ti-doped MoS₂ coatings on HSS, whereas a smooth curve behaviour was found for Al-doped MoS₂ on HSS. In agreement with the OCP measurements the corrosion potential E_corr in potentiodynamic corrosion tests was the highest for undoped MoS₂ coatings on glass or HSS substrates. After the potentiodynamic corrosion tests a strong corrosive attack could be found for all coatings. In salt spray tests the lowest number of corrosion pits was found for the undoped MoS₂ coating on HSS.
11:30 AM		B7-3-11 Historical Perspective on Surfaces F. Monnoyeur (Carnegie Mellon University) A scientist can look at surfaces from various perspectives. This presentation intends to identify how scientists have been conceiving surfaces at the main periods of scientific development. In the Myth of the Cave, Plato opposes our spontaneous approach to the scientific approach of reality. By looking at objects, we only see the surface or the superficiality of objects; but, by thinking, we can discover the real nature of objects. In this opposition surfaces are mere apparitions of objects, but not the objects themselves. For Plato, surfaces are in fact misleading. On the contrary, Descartes defines a body by its surface, which corresponds to a measurable geometrical figure. Because surfaces are used primarily to measure bodies, they are a necessary step in the scientific investigation. Today scientists can relate to surfaces by giving credit to what they see. For instance, they see the surface of the substrate to be coated. In that case the surface is treated as a mere extension without depth. This extension is observable with an optical microscope and allows the scientist to define surfaces as being rough, colored, cracked, etc. Another way to look at a surface is to consider that it has a depth, which means it is composed of several layers of atoms linked by a common property, such as hardness, crystallinity or composition. From this standpoint, we can consider that the bulk of the object starts with the change of the property of the atoms. At last, how can we define the role of what we call the interface between two media, for instance, between the substrate and a coating? Leonardo Da Vinci supported the idea that the contact between water and air had no reality. Therefore, for Da Vinci, the interface was a pure abstraction without physical existence and was used to indicate an arbitrary separation. However for the scientist today, the interface is the necessary physical intermediary able to operate the transition between the two media.