ICMCTF2003 Session B7: Properties And Characterization Of Hard Coatings And Surfaces

Thursday, May 1, 2003 1:30 PM in Room Golden West

Thursday Afternoon

Start	Invited?	Item
1:30 PM	Invited	B7-1 Effect of Ion Bombardment on Properties of Hard Sputtered Films J. Musil, H. Polakova, J. Vlcek, J. Suna (University of West Bohemia, Czech Republic) It is well known that the energy E_pi delivered to the growing film by bombarding ions has a crucial effect on its structure and so on its physical and functional properties. In a collisionless discharge this energy can be determined from three easily measured quantities, i.e. the substrate bias U_s, the substrate ion current density i_s and the deposition rate a_D of the film, according to the formula E_pi = E_i ν_i/ν_c ~ U_s i_s/a_D, where E_i is the ion energy, ν_i and ν_c is the flux of ions and condensing particles, respectively. This means that E_pi strongly depends not only on U_s and i_s but also on a_D. This fact is of extraordinary importance in reactive deposition of compounds, such as nitrides, oxides, carbides, etc. A change in the partial pressure of reactive gas (N₂, O₂, CH₄, etc.), under constant deposition conditions, affects not only amount of reactive gas atoms in the growing films but it can also result in large changes in a_D and hence in the E_pi values. For instance, for nitrides a_D(Me) = (3-4) a_D(MeN) and for oxides even a_D(Me) = (10-15) a_D(MeO), where Me is a metal, MeN and MeO is a metal nitride and metal oxide, respectively. This paper reports on the effect of the E_pi values on (1) development of the structure of nitrides, (2) desorption of N from reactively sputtered nitrides, (3) resputtering of the growing film and (4) mechanical properties of hard Ti(Al,V)N_x and Ti(Fe)N_x nitrides. Besides, it is shown that the delivered energy E_pi is necessary but not a sufficient condition to form the film with a maximum hardness H_max. To produce the film with H_max two conditions must be fulfilled: (1) the energy E_pi must be greater than E_pi,min and (2) the film must have an optimum structure.
2:10 PM		B7-3 Synthesis and Characterization of Nanolayered TiB₂/TiC Coatings for Possible Elevated Temperature Applications K.W. Lee, Y.-W. Chung, L. Keer, K.. Ehmann (Northwestern University) Multilayered coatings composed of 3 nm TiB₂ and various individual layer thicknesses of TiC were synthesized using non-reactive dual-cathode magnetron sputtering techniques with substrate rotation on silicon (001), M2 steel and WC cutting inserts. The two coating materials were chosen for their high hardnesses, melting temperatures, and immiscibility between different crystal structures. The goal of the research is to synthesize hard and chemically stable coatings that provide wear protection at high contact pressures and temperatures. Under appropriate deposition conditions, we obtained coatings with TiB₂(001) preferred orientation. Room-temperature hardness of these coatings approaches 60 GPa, far exceeding the rule-of-mixture value. High-resolution transmission electron microscopy and low-angle x-ray diffraction studies confirmed that the layer structure of these coatings was preserved after one-hour annealing in argon at 1000°C. Scanning electron microscopy shows that coatings were subjected to oxidation at 800°C in an oxygen-containing environment. Wear and durability tests on coated M2 steels demonstrated the improved room temperature tribological performance of these coatings under unlubricated conditions compared with standard coatings such as TiN. Actual dry machining on coated C3 WC cutting inserts was performed using 1018 steel and aluminum 319. Scanning electron microscopy and white-light interferometry were used to evaluate durability of these coatings before and after machining. All coated tools out-performed the uncoated tool. Among them, the TiB₂ and multilayer (TiB₂ : TiC = 3:1) coatings show the best performance. These results will be presented and discussed in terms of the coating's potential in dry machining and high-temperature tribological applications.
2:30 PM		B7-4 Study of Oxidation and Wear Behaviors of (Nb,Cr)N Thin Films Using Raman Spectroscopy J.H. Hsieh (School of MPE, Nanyang Technological University, Singapore 639798, Singapore); C. Li (Nanyang Tech. University, Singapore); L.K. Tan (Singapore Institut of Manufacturing and Technology, Singapore); N.J. Tan (IMRE, Singapore) Several (Nb,Cr)N coatings were deposited by an unbalanced magnetron sputtering system. The tribological properties of these coatings were then studied using a ball-on-disk setup with alumina balls. The wear debries were then examined using Raman spectroscopy. The results were compared with those obtained on furnace-oxidized coatings. By comparing these results, we are able to explain why Cr-riched coatings were subjected to polishing wear, while Nb-riched coatings were subjected to ploughing wear. In addition, some of the coatings were oxidized by oxygen plasma, followed by Raman spectroscopy study. The difference in oxide structure was discussed.
2:50 PM		B7-5 New Metastable Hard Coatings in the System V-C-Al-N S. Ulrich, J. Baumgart, K. Sell, M. Stueber, J. Ye (Forschungszentrum Karlsruhe, IMF I, Germany); H. Holleck (Forschungszentrum and University Karlsruhe, Germany) New metastable nanocrystalline (V,Al)(C,N) hard coatings with f.c.c structure were deposited by r.f.-magnetron sputtering of a composite target (VC : AlN = 60 mol% : 40 mol%) in a pure argon discharge. The chemical composition was determined by microprobe analysis. The metastable structure of the films was characterized experimentally by means of X-ray and electron diffraction as well as high resolution transmission electron microscopy. Furthermore, the influence of the deposition parameters on the film properties such as Vickers hardness (1850 - 3260 HV0.05), Young's Modulus (450 - 480 GPa), adhesion and wear behaviour is described. The conditions for the formation of metastable (V,Al)(C,N) coatings are compared with that of metastable (Cr,Al)N- and metastable (Ti,Al)N thin films and discussed in terms of thermodynamic calculations and estimations.
3:10 PM		B7-6 Influence of Deposition Parameters on the Wetting Behavior of Magnetron Sputtered Chromium Nitride Films A. Hieke, K. Bewilogua (Fraunhofer Institute for Surface Engineering and Thin Films, Germany) For many applications in the areas of forming, cutting, punching, pressing and molding chromium nitride (CrN_x) coatings were applied very often. Beside the well known tribological properties of CrN_x films low sticking properties are also very important. One method to characterize the wetting properties of a film surface is the surface energy measurement. By investigations on different CrN_x coatings surface energy values over a wide range from 30 mN/m up to 75 mN/m could be measured. Such surface energy values corresponded to water contact angles from 120° down below 5°. That means, the surface properties of CrN_x films can be hydrophilic or hydrophobic. Detailed investigations of our CrN_x coatings, which were prepared by reactive DC magnetron sputtering in a argon/nitrogen atmosphere, will be reported. Correlation’s between deposition parameters, especially the ion current density during film growth as well as the nitrogen content in the coatings and the surface energy were revealed. Furthermore we will present results on the surface topography, on the chemical composition in the surface near region down to about 50 nm depth and on the long time stability of the surface energy values. Considering these data an interpretation for the different wetting properties of CrN_x films will be given. Note: Requested an Oral Session.
3:30 PM		B7-7 Structural and Mechanical Properties of Ti_1-xAl_xN Films Deposited by Reactive Unbalanced Magnetron Sputtering P.W. Shum, K.Y. Li, Z.F. Zhou, Y.G. Shen (City University of Hong Kong, PR China) Thin Ti_1-xAl_xN films, with 0≤x≤1.0 (0.7 µm thick), were deposited onto unheated silicon (100) substrates by reactive unbalanced magnetron sputtering at a bias voltage of -60 V in an Ar-N₂ gas mixture. The effects of aluminium concentration on the structural and mechanical properties of these films have been studied. The films were analyzed by x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), cross-sectional scanning electron spectroscopy (SEM), atomic force microscopy (AFM) and nanoindentation measurements. Ti_1-xAl_xN films were first analyzed by XPS in order to determine the chemical bonding configuration and the atomic concentration of elements. The XRD scans exhibited the structural changes in the Ti_1-xAl_xN films with different Al concentrations. It was found that at x < 0.3, the films were essentially B1-NaCl TiN. A two-phase structure of B1-NaCl (TiN) and Wurtzite (AlN) was observed in the range of x = 0.48-0.57. It is interesting to note that the nature of the AlN (002) orientation changes drastically at x=0.57. A single-phase structure of AlN was formed as x=1.0. By nanoindentation measurements, it was observed that the hardness of the TiN film at x=0.0 was 23 GPa. The hardness was increased when the value of x increased and reached a maximum value of 32 GPa at x=0.48. With further increase in x, the hardness of the film dropped. The hardness had a lower value of 21 GPa for x=1.0. The evolution of the microstructure of the films by cross-sectional SEM revealed that both TiN and AlN films had a columnar structure, while the film prepared at x=0.5 had a dense and fine grained structure. Further measurements by AFM indicated that the film at x=0.5 also showed the finest surface topography. By analysis, it is concluded that the maximum hardness coincides with a minimal grain size, which implies a high density of grain boundaries.
3:50 PM		B7-8 Relationship Between an Affinity of (Ti_1-x, Al_x)N Layer Toward Iron and its Cutting Performance H. Takaoka, E. Nakamura, T. Oshika, A. Nishiyama (Mitsubishi Materials Corporation, Japan) For the purpose of improving the wear resistance of cemented carbide cutting tool, (Ti, Al) N hard coating layer is widely used. In this study, the relationship between affinity of (Ti_1-x, Al_x)N layer toward iron and its cutting performance was investigated. (Ti_1-x, Al_x)N films that have various aluminum contents were deposited on cemented carbide substrates by cathodic arc ion plating method, and iron films were further deposited on them by same method. The affinity of (Ti_1-x, Al_x)N films toward iron was determined using above samples after they were annealed in a furnace. The status of interfaces between iron films and (Ti_1-x, Al_x)N films were analyzed by Auger electron spectroscopy (AES). Cutting performances of (Ti_1-x, Al_x)N films coated cemented carbides were evaluated by steel turning and milling.
4:10 PM		B7-9 A Comparative Study of the Corrosion Behaviour of Hard Nitride Coatings on Iron-based Substrates M. Fenker, M. Balzer, H. Kappl (Forschungsinstitut für Edelmetalle und Metallchemie, Germany) Hard nitride coatings (TiN, TiBN, CrN, NbN) were deposited onto high speed steel and alpha-iron using reactive magnetron sputtering. The corrosion behaviour of the samples was studied by electrochemical corrosion tests in 0.8 M NaCl solution and by salt spray tests. All investigated coating materials own a very high corrosion resistance itself against corrosive media. However, localised corrosion (e.g. pitting corrosion) of the coating systems was observed, when exposed to a corrosive medium. This detrimental failure of the coating systems is due to defects present within the coating. Two kind of defects were detected for our coatings: i) macro-defects, clearly visible in an optical microscope (size 10-100 µm) and ii) nano-defects, even not visible using a scanning electron microscope (SEM). The nano-defects could only be observed using a copper decoration test. Using this test we have counted 58 decorated sites (i.e. pores) on an area of 10x10 µm² for a NbN coating surface, despite the fact that for this coating no columnar structure could be observed by SEM. Optical inspection of the coating surface before and after potentiodynamic corrosion tests of the samples has lead us to the assumption that the macro-defects are responsible for the step-like increase of the current density and hence for detrimental coating failure. This kind of corrosion behaviour could be found for nearly all investigated nitride/steel systems to different extent and will be discussed with respect to the formation and existence of macro-defects.
4:30 PM		B7-10 Microstructure Evaluation and Strengthening Mechanism of Ni-P-W Alloy Coatings F.B. Wu, J.G. Duh (National Tsing Hua University, Taiwan, ROC) Ni-P-W alloy coatings were deposited onto AISI420 steel substrate by both r.f. magnetron sputtering and electroless plating techniques. The coating hardness was investigated through the microhardness testing with a Knoop indenter. The strengthening mechanism of the Ni-P-W coatings in both as-deposited and heat-treated states were described with respect to compositional distribution and microstructural evolutions. In the as-deposited state, when all the coatings were amorphous, the hardness of the alloy films increased with increasing W and decreasing P. After heat treatment, the coatings were strengthened by the precipitation of Ni-P compounds and solutioning of W in the crystallized Ni matrix. Quantitative analysis for the strengthening effect of the Ni-P-W coatings was performed based on the elemental concentrations, Ni-P compound precipitation and NiW matrix ratio. The heat-treated Ni_76.7P_15.9W_7.4 coating showed the highest peak hardness of 1800 HK_0.005 when the maximum W solution limit in the Ni matrix was reached. The degradation in coating hardness under heat treatment was also discussed with respect to W element and Ni-P precipitation incorporated in the Ni-P coating.
4:50 PM		B7-11 Elastic Properties of nc-TiN/a-Si₃N₄ Nanocomposites Films by Surface Brillouin Scattering M.H. Manghnnani, P.V. Zinin, S. Tkachev (University of Hawaii); S. Veprek, P. Karvankova (Technical University Munich, Germany); C. Glorieux (Katholieke Universiteit Leuven) Elastic Properties of nc-TiN/a-Si₃N₄! Nanocomposite Films by Surface Brillouin Scattering *Nanocomposite (nc) films developed recently exhibit extremely high values of hardness¹. To model the behavior of the nanoindenter in case of such a nanocomposites, it is necessary to know the distribution of the elastic properties of the film at the vicinity of the surface. We used Surface Brillouin Scattering (SBS) to determine the elastic properties of the nc-TiN/a-Si₃N₄ film at depth from 50nm to 400 nm. In the case of nc-TiN/a-Si₃N₄ films, the Rayleigh mode can be clearly identified in the Brillouin spectra. Surface acoustic waves (SAW) velocity dispersion curve has been measured at the frequency range from 7.3 GHz till 17.6 GHz. At this frequency range velocity of the SAWs decrease from 5.69 km/s to 4.75 km/s. To model the variation of the elastic properties with depth we used an algorithm proposed by Glorieoux et al.² . Simulation shows that Rayleigh wave velocity increases from 3.5 km/s at the depth of 50 nm to 6.0 km/s at 400 nm. Our results demonstrate that the elastic properties of the film are highly inhomogeneous, and the velocity of Rayleigh wave increases with depth. ¹Veprek, S., The Search for Novel, Superhard Materials, Journal of Vacuum Science & Technology A 17 (5), 2401-2420, 1999. ²Glorieux, C., Gao, W., Kruger, S. E., Van de Rostyne, K., Lauriks, W., and Thoen, J., Surface Acoustic Wave Depth Profiling of Elastically Inhomogeneous Materials, J. Appl. Phys. 88 (7), 4394-4400, 2000.