Papers

ICMCTF2004 Session B7-2: Properties and Characterization of Hard Coatings and Surfaces

Monday, April 19, 2004 1:30 PM in Room Golden West

Monday Afternoon

Start	Invited?	Item
1:30 PM		B7-2-1 Thermal Behaviour of Si-containing Nanocomposite Coatings in Oxidant Atmosphere A. Cavaleiro (Coimbra University, Portugal) In recent years, a significant part of the research work carried out on the "Hard Coatings" field is concerned with the development of nanocomposite structures. The envisaged improvement in the mechanical properties is based on the achievement of a multiphase structure consisting in a nanocrystalline hard phase enrobed by a very thin layer (<1nm) of an amorphous/crystalline phase. Among the systems studied, TM-Si-N (TM=transition metal) was the one that attracted more attention. Detailed results of the mechanical characterization of these coatings are abundant in literature. However, in spite of most of the applications of these coatings include high temperature and aggressive media (e.g. cutting and forming tools), only in a few cases, studies were performed for evaluating the oxidation resistance. In the first part of this contribution, a review of the main results in the literature about the thermal and oxidation behaviour of Si-containing films (TM-Si-N) will be presented. The oxidation mechanisms will be compared and discussed as a function of the TM element, the as-deposited grain size and the Si content. A survey of the type of oxide and the calculated apparent activation energies will be given. In a second part, more detailed results about W-Si-N films deposited by sputtering will be shown. The Si content has significant influence on different factors, e.g. the structure, the grain size, the cross section morphology, which from their side determine the final oxidation resistance of the coatings. Moreover, the effect of the type of material used as substrate on the thermal behaviour of the W-Si-N films is also important in the global oxidation behaviour of the coated samples. The oxidation rates will be presented and the results will be interpreted as a function of either the structure of the oxide scale and its mechanical stability during cooling down to room temperature or the grain size and morphology of individual oxides.
2:10 PM		B7-2-3 Investigation of the Properties of Al_1-xCr_xN Coatings Prepared by Cathodic Arc Evaporation A. Reiter, B. Hanselmann (Balzers Ltd., Liechtenstein); V.H. Derflinger (Balzers AG, Liechtenstein); T. Bachmann (Balzers Ltd., Liechtenstein); W. Kalss (Balzers AG, Liechtenstein) Al_11-xCr_xN coatings prepared by different deposition techniques "mainly by reactive sputtering" were investigated in the past, where the good oxidation and wear resis-tance in comparison to Ti(1-x)Al(x)N-coatings were found. In this work Al_1-xCr_xN films are deposited from Al_1-xCr_x targets with various composition (0
2:30 PM		B7-2-4 Low Friction Coatings for Cutting Tools M. Kathrein (CERATIZIT Austria Ges.m.b.H., Austria); M. Stoiber (Plansee AG, Austria); W. Wallgram, R. Venturini, U. Schleinkofer (CERATIZIT Austria Ges.m.b.H., Austria) High wear resistant coatings like Al₂O₃ are widely used in high performance cutting operations. Especially for multifunctional cutting tools the need for low friction properties besides high wear resistance gained increasing importance. Thus, the aim of this work was to develop a tribologically improved Al₂O₃ coating with high wear resistance but also with considerable low friction properties. Coating structure and chemical composition were characterized using scanning electron microscopy (SEM), wavelength-dispersive electron probe microanalysis (EPMA), and X-ray diffraction (XRD, HT-XRD). The tribological properties of the coatings were evaluated using a ball-on-disc tribometer. For the coatings evaluated, a remarkable influence of the deposition temperature on the grain size and a corresponding decrease of the friction coefficient was observed. Phase analysis showed the presence of higher chlorine and Ti_nO_2n-1 contents at lower deposition temperatures where the formation of Ti_nO_2n-1 - phases in the mixed oxide structure was found to provide the coating with beneficial low friction properties. These advantageous effects were observed over a wide temperature range in tribological tests. Furthermore, cutting tests confirmed improved performance of cutting tools.
2:50 PM		B7-2-5 Relationship between Film Properties and Wear Resistance for Various (Ti_1-x,Al_X)N,(x=0,0.25,0.5) Coated Cutting Tools Prepared by Cathodic Arc Ion Plating Method. E Nakamura, H. Takaoka, K. Okada, T. Ohshika, A. Nishiyama (Mitsubishi Materials Corporation Central Research Institute Naka Research Center, Japan) It is well-known that the cutting performance of the (Ti,Al)N coated cutting tools is superior to the TiN coated one in various cutting operations, especially in milling of steels. It is generally recognized that these fairly high performance of (Ti,Al)N film is attributed to its high oxidation resistance and high hardness. In this work, the characteristic of (Ti_1-X,Al_X)N,(x=0,0.25,0.5) films at high temperature was measured. The wear mechanism was investigated by field emission-type transmission electron microscope (FE-TEM). Then relation between Al contents of (Ti_1-X,Al_X)N films and mechanism of flank face wear in steel milling conducted in dry condition was investigated. (Ti_1-X,Al_X)N,(x=0,0.25,0.5) films were deposited on WC-Co substrates using a cathodic arc ion plating method. Film characteristics at high temperature were examined by TG-GTA, High Temperature Micro Vickers Hardness Tester. For the aim of clarifying wear mechanism, sample having flank face wear width of 0.1mm was observed in detail by FE-TEM, and then an interesting result was obtained. Relationship between Al contents of (Ti_1-X,Al_X)N films and wear mechanism will be discussed with taking high temperature characteristics of films into account.
3:10 PM		B7-2-6 Mechanical Properties of Functionally Graded Titanium Carbide Thin Films J.M. Anton, B. Mishra (Colorado School of Mines); F. Kustas (Engineered Coatings, Inc.) Titanium Carbide thin films have many properties that make them useful for wear resistant applications, including high hardness, high toughness, and low coefficient of friction against steel. Several studies have shown that a film possessing a graded composition will improve the adhesion of the film to the substrate (titanium rich at the substrate, carbon rich at the surface). These studies have been carried out using high energy PVD methods such as pulsed laser deposition and cathodic arc deposition. Here we investigate forming a graded composition by unbalanced magnetron sputtering with a pulsed graphite target. Sputtering can be a more cost effective and readily available method for depositing films with a graded composition. The films' mechanical properties are evaluated by hardness testing, scratch testing, and friction measurements. Previous work on sputtered TiC films has yielded results by which to compare mechanical properties of the graded films. We expect that the film's adhesion will be improved by the graded composition as has been shown with other deposition techniques.
3:30 PM		B7-2-7 Production and Characterization of Nanocomposite Mo-N-Cu Coatings Produced by Arc and Magnetron Sputtering Physical Vapor Deposition Techniques O.L. Eryilmaz (Argonne National Laboratory); M. Urgen (Istanbul Technical University, Turkey); A. Erdemir (Argonne National Laboratory); A.F. Cakir (Istanbul Technical University, Turkey) In this study, a series of novel nanocomposite Mo-N-Cu coating systems has been produced and studied. These coatings were applied to high speed steel substrates by cathodic-arc and magnetron sputtering physical vapor deposition. Coating microstructure and chemistry were varied by controlling Mo or Cu cathode current density or the target power ratios. The coatings were analyzed by x-ray diffraction in thin film mode (angle of incidence 1°) by using CuKa radiation. The average grain size was calculated by the Scherrer formula. Ultra microhardness tests were applied to determine the coating hardness and elastic modulus. The microstructure was investigated by cross-sectional scanning electron microscopy. The friction and the wear behavior were also investigated in open air and dry nitrogen environment. The relationships among average grain size, hardness, elastic modulus, and microstructure of the resultant films are presented.
3:50 PM		B7-2-8 Investigation of Magnetron Sputtered Ti-Cu-Ni Coatings S. Bengelsdorff, H.-R. Stock, P. Mayr (Stiftung Institut fuer Werkstofftechnik, Germany) The replication of optical components like lenses requires an exceptional smooth surface of the moulding tools. Ultraprecision cutting with diamond tools is most suited to achieve these optical surfaces. Due to high chemical wear of the diamond tools steel surface cannot be machined with diamond tools. Up to now, electroless nickel is the hardest material, which can be machined with diamonds, but hardness and temperature stability of these coatings are limited. It could be shown, that titanium copper nitride is a promising alternative. Depending on the chemical composition the hardness is significantly higher and the interaction with diamond is negligible¹. Therefore, Ti-Cu-N coatings with 10-18 at.% copper were deposited on high speed steel (AISI M2) by reactive magnetron sputtering. The chemical composition, ex-situ determined by glow discharge optical spectroscopy (GDOS), was varied by using composite titanium targets with different number of copper inserts and adjusting the nitrogen gas flow. Ultra-microhardness measurements show a plastic hardness of about 18 GPa. Scratch test reveals a critical load of 60 N. The coating thickness, determined by secondary electron microscopy (SEM), ranges between 10 and 18 µm. However a minimal thickness of about 15 µm is necessary for the subsequent grinding and polishing process. First grinding tests with single crystal diamond tools on Ti-Cu-N coatings results a surface roughness (Ra) down to 20 nm, determined by white light interferometry (WLI). This deposited Ti-Cu-N are potentially useful for moulding tools. ¹ A. Vennemann et al., Surf.Coat.Technol.,174-175 (2003) 973.
4:10 PM		B7-2-9 Structural, Chemical, Optical and Mechanical Properties of ZrN/Ag Nanocomposite Coatings M. Debessai (Southern Illinois University); D. Mihut, S.L. Rohde (University of Nebraska-Lincoln); S.M. Aouadi (Southern Illinois University) Nanocomposite films of ZrN/Ag were prepared using reactive unbalanced magnetron sputtering and their structural, chemical, optical, and mechanical properties were investigated as a function of film composition, substrate bias, and substrate temperature. X-ray diffraction spectra revealed broad peaks that correspond to nanocrystalline ZrN. Diffraction peaks corresponding to pure silver were observed only for films with a silver content in excess of 28 at.%. The grain size was evaluated using the Scherrer formula and was found to depend on the three deposition conditions investigated in this study. In addition, substrate bias in excess of -100 V caused the films to be textured in a preferential (111) orientation. XRD findings were confirmed by transmission electron microscopy. The chemical and phase composition were deduced from X-ray photoelectron spectroscopy (XPS). The dielectric function was measured using spectroscopic ellipsometry and yielded information about the structural and optical properties of the films. For example, the conduction electron mean free path was deduced from the Drude-Lorentz model and was correlated to the grain size. The nanohardness and elastic modulus was measured by nanoindention. The resistance to plastic deformation, as measured by the ratio H₃/E₂, was optimized with a silver content of 15% and a substrate bias of -100 V. Finally, the nanotribological behavior of these films was studied using nanoscratch techniques.
4:30 PM		B7-2-10 Changes in Surface Texture of Hard Cr-N Coating Produced by PAPVD after Plasma Nitriding C. Godoy (Universidade Federal de Minas Gerais, Brazil); V.T.L. Buono (School of Engineering-UFMG, Brazil); J.C. Avelar-Batista (Tecvac Ltd., Brazil); R.D. Mancosu, J.K. Morais (Universidade Federal de Minas Gerais, Brazil) It has already been reported that duplex coatings, consisting of plasma nitriding of steel substrates and subsequent deposition of hard coatings by PAPVD (Plasma-Assisted Physical Vapour Deposition), can improve wear and impact resistance due to their superior load support capability. However, depending on the conditions of the deposition process, film defects such as pores and pinholes, different crystalline structures and surface textures can develop, compromising the coating performance. Duplex coatings were produced in this work, using an Ar sputtering mechanism to remove the iron nitride layer and thus prevent the occurrence of compound layer desestabilization. A non-duplex Cr-N coating was also produced for comparison. The changes in surface texture due to this sputter etching by argon/nitrogen ions were analyzed by a 3D topographical method. Glow discharge lamp spectroscopy, x-ray diffraction, scanning electron microscopy and microprobe analysis were employed to evaluate other characteristics of the coatings and the AISI H13 steel substrate. Higher values of the amplitude parameters (Sa, Sq, Sp, Sv, St) were found for the duplex coating relative to the non-duplex Cr-N coating. The height distribution parameters (Ssk, Sku) indicated a surface similar to the nitrided steel, having more outliers. The bearing area ratio curve of the duplex system and its functional parameters (Spk, Sk and Svk) confirmed a rougher surface. For all coated systems, the surface bearing index (Sbi) was higher than for the non coated steel, indicating a better bearing property. The worse response of duplex multiphase coating in potentiodynamic tests (1N H₂SO₄ solution), as compared with a non-duplex Cr-N coating was related with surface texture modification. Nucleation of pits were observed by perfilometry to happen in the outliers of the duplex coating. The intensity of X-ray diffraction peaks in non duplex Cr-N coatings corroborate its smoother surface.
4:50 PM		B7-2-11 Effect of Nitrogen Flow Rate on the Structure and Mechanical Properties of ZrN Thin Film on Si(100) and Stainless Steel Substrates J.H. Huang, C.H. Ho, G.P. Yu (National Tsing Hua University, Taiwan, R.O.C.) Nanocrystalline ZrN films were successfully deposited on Si (100) and AISI 304 stainless steel substrates using hollow cathode discharge ion plating (HCD-IP) system. The effect of nitrogen flow rate (ranging from 5 to 35 sccm) was investigated on the N/Zr ratio, structure, and mechanical properties of the ZrN film. The results showed that the variation of nitrogen flow rate did not significantly affect the film thickness, preferred orientation and hardness. The major effects of the nitrogen flow rate on the ZrN film were N/Zr ratio, packing factor, and grain size. The N/Zr ratio increased (0.6 to 0.9) with increasing nitrogen flow rate. The grain sizes of the ZrN films, measured by both X-ray diffraction (XRD) and scanning electron microscopy (SEM), ranging from 15 to 30 nm, generally decreased with increasing nitrogen flow rate. The hardness of the nanocrystalline ZrN film was not related to the variation of the residual stress. The deformation mechanism of the ZrN film may be through grain rotation or grain boundary sliding instead of slip by dislocations. Due to higher electric conductivity, 304 stainless steel substrate attracts more Zr ions than Si substrate. This leads to larger coating thickness, roughness, and residual stress for the ZrN film deposited on stainless steel than on Si substrate.