Papers

ICMCTF2004 Session B8-1: Hard and Multifunctional Nano-structured Coatings

Tuesday, April 20, 2004 8:30 AM in Room Golden West

Tuesday Morning

Start	Invited?	Item
8:30 AM		B8-1-1 Nano Crystalline (Al,Ti,Si)N Coatings for High Speed Cutting Tool Applications of Hardened Work Materials Y. Tanaka, A. Kondo, K. Maeda (Mitsubishi Materials Kobe Tools Corporation, Japan) Nano crystalline (Al,Ti,Si)N coatings were deposited on WC-Co substrates using a cathodic arc ion plating method. The structures and the compositions were characterized by X-ray diffraction (XRD), Transmission electron microscopy (TEM) and X-ray photoelectron spectrometer (XPS), and the mechanical properties were evaluated by indentation tests and ball-on-disk wear tests. Codeposition process from different composition targets enabled to control the structure of the film and high hardness over 37 GPa was obtained with nano crystalline structures. Addition of Si improved oxidation resistance and mechanical properties and these were discussed with the film structure and composition. The high speed cutting performances on hardened die steels and Inconels were investigated by using coated carbide endmills. Nano crystalline (Al,Ti,Si)N coatings showed greatly improved cutting performances, especially on high hardness work materials of over 60 HRC . Wear mechanism and cutting characteristics were discussed with the structures and properties of the films.
9:10 AM		B8-1-3 Structure Refinement on Hardness Enhancement and Fracture Behaviour of TiAlN-based Nanocomposite Thin Films D. Sarangi, A. Karimi (EPFL, Switzerland); M. Morstein, T. Cselle (Platit AG, Switzerland); A. Schütze (Balzers AG, Liechtenstein); M. Tobler (IonBond AG, Switzerland) Hard thin films based on TiAlN nitrides are used to improve performance of cutting tools. Recent developments showed that the nanocomposite version of these nitrides exhibit overall mechanical properties much better than the average of the constituent phases, in particular, fracture toughness which is very important regarding wear resistance and reliability of thin films. In this paper we first present the atomistic aspects of the formation of nanostructures in TiAlN-based nitrides using HRTEM together with local chemical analysis. The role of Al and Si on the occurrence of nanoclusters inside the grains, segregation at the grain boundaries, accommodation of secondary phases will be highlighted with respect to continuous nucleation process conditions under arc-plasma deposition. In the second part we will show mechanical properties measured using depth sensing nanoindentation techniques. Hardening mechanisms based on interface driven phenomena, structure barriers strengthening, coherency stresses will be discussed considering earlier models by Veprek, Barnett etc. Emphasis will be made on fracture modes and mechanisms, both of them strongly influenced by quality of grain boundaries as shown by TEM observation of FIB cross sectioned samples. The crack modes will be discussed in terms of different deformation mechanisms that happen during indentation of these thin films.
9:30 AM		B8-1-4 Effect of Element Addition on Structural and Mechanical Property of (Ti,Cr,Al)N Coating Deposited by a Hybrid Coating System K. Yamamoto, S. Kujime, K. Takahara (Kobe Steel Ltd., Japan) Previously, we reported formation of superhard ternary nitride (Ti,Cr,Al)N coatings with high Al contents deposited by a new plasma enhanced cathode. In this work, effect of additional elements, such as B and C, on the structural and mechanical properties of (Ti,Cr,Al)N coatings was investigated. Depositions of (Ti,Cr,Al)N coatings with additional elements were conducted by a new hybrid coating system wequipped with arc and UBMS (unbalanced magnetron sputter) sources in the same process chamber. The arc source was used to deposit (Ti,Cr,Al)N coating and additional elements were sputtered from the UBMS source. In case of B and C addition, an electro-conductive boron carbide was used as a sputter target. The structure and mechanical properties of the resultant coatings were investigated against the concentration of the doped elements.
9:50 AM		B8-1-5 Tribological Characterisation of Hard Si-based TiN Coatings: the Effect of Composition and Ion Bombardment G.G. Fuentes, R.J. Rodríguez, R. Martínez (Asociación de la Industria Navarra, Spain); S. Carvalho, F. Vaz, L. Rebouta (Universidade do Minho, Portugal); E. Alves (ITN, Portgual); Ph. Goudeau, J.P. Rivière (University of Poitiers, France) This work reports on the tribological performance of (Ti,Si)N nanocomposite coatings as a function of composition and the ion beam bombardment during growth. The coatings were deposited onto silicon and polished high-speed steel (HSS) substrates, by dc reactive magnetron sputtering in the presence of ion beam bombardment. The stoichiometry of the films was investigated by Rutherford backscattering spectrometry (RBS), and the coating densities were derived by combination of RBS and thickness measurements. In the presence of ion bombardment, the coatings developed a two fcc-phase mixture with some degree of compressive stress, i.e. the first phase identified as a fcc TiN (a₀ = 0.429 nm), and a second consisting on a fcc Ti_1-xSi_xN_y (a₀ = 0.418 nm). This latter could be a so-called solid solution where some Si atoms are probably occupying Ti positions in the TiN matrix. Without ion bombardment, only the solid solution was detected. The results of the tribological tests are discussed in terms of the changes in the structural properties of the coatings. We have observed that the nanostructured coatings exhibited better tribological performance than that showed by the coatings deposited in the absence of ion bombardment. The degree of improvement of the tribological properties are discussed in terms of the temperature and the bombarding conditions. The reported results confirm the potential benefits of the ion beam bombardment during coating deposition for the protection of metal tools, forming moulds or different HSS based components working under strong abrasive conditions.
10:10 AM		B8-1-6 A New Low Friction Concept for Ti-Al-N Coatings in High Temperature Applications K. Kutschej (Materials Center Leoben, Austria); P.H. Mayrhofer, C. Mitterer (University of Leoben, Austria); M. Kathrein (CERATIZIT Austria AG, Austria) Ti-Al-N hard coatings are well established in commercial applications - especially for extreme conditions, like dry machining - due to their excellent oxidation and abrasion resistance. For further improvement, different elements may be added. Especially, V offers promising lubricious phases due to the formation of easily shearable oxides (often also referred to as Magneli phases) at temperatures higher than 500 °C. Recently, TiAlN/VN superlattice coatings were developed, where excellent mechanical properties are combined with low friction by alternate layering of TiAlN and VN. In order to develop coatings with more uniform properties V has to be directly incorporated into the TiAlN coating. Thus, the aim of this work was to prepare Ti-Al-V-N coatings with different contents of V to verify the concept of lubricious oxides while maintaining the excellent mechanical properties of Ti-Al-N. An unbalanced D.C. magnetron sputtering system was used to deposit coatings from powder metallurgically prepared Ti-Al-V targets with 2, 5 and 10 at% V in an Ar+N₂ discharge. Coating chemical composition and structure were characterized by wave length dispersive electron probe microanalysis and X-ray diffraction. Mechanical and tribological properties are obtained from microindentation and high temperature ball-on-disc tests against Al₂O₃ and austenitic steel balls. By direct incorporation of V, coating hardness could be increased from 35 to 45 GPa. Increasing the testing temperature from ambient to 700 °C, the friction coefficient could be lowered from above 1 to 0.6 due to the formation of lubricious oxides. Finally it could be shown that by alloying of V to Ti-Al-N coatings, their tribological properties could be improved by the lubricious oxide concept.
10:30 AM		B8-1-7 Hypersonic Plasma Particle Deposition of Si-Ti-N Nanostructured Coatings J. Hafiz, X. Wang, R. Mukherjee, W. Mook, C. Perrey, J. Deneen, J.V.R. Heberlein, P.H. McMurry, W.W. Gerberich, C.B. Carter, S.L. Girshick (University of Minnesota) Si-Ti-N nanoparticle films were deposited using hypersonic plasma particle deposition.¹ In this method vapor phase precursors (TiCl₄, SiCl₄ and NH₃) are dissociated in a DC plasma arc and the hot gas is quenched in a rapid nozzle expansion to nucleate nanoparticles. These nanoparticles are then accelerated in hypersonic flow, causing them to deposit by inertial impaction on a substrate placed downstream of the nozzle. Films of 20-25 microns thickness were deposited on molybdenum substrates at rates of 2-10 µm/min, depending on reactant flow rates, at substrate temperatures ranging from 250 to 850 C. In separate experiments with the same conditions, particle size distributions were measured by placing a sampling probe at the same location as the film substrate. The sampled aerosol was rapidly diluted and delivered to a scanning mobility particle sizer. Measured particle diameters were typically concentrated in the 5-10-nm range, with higher reactant flow rates producing larger particles. Microstructural characterization of the films was performed using scanning and transmission electron microscopy, Rutherford backscattering, X-ray photoelectron spectroscopy and X-ray diffraction. Focused ion beam milling was used to observe film cross section and porosity. Hardness of as-deposited films was evaluated by nanoindentation of polished film cross-sections. Measured hardness values, averaged over 10-15 locations for each film, equaled 22-24 GPa. ¹N. P. Rao, N. Tymiak, J. Blum, A. Neuman, H. J. Lee, S. L. Girshick, P. H. McMurry and J. Heberlein, J. Aerosol Sci. 29, 707 (1998).
10:50 AM		B8-1-8 The Issue of the Reproducibility of the Deposition of Superhard Nanocomposites with Hardness of ≥ 50 Gpa S. Veprek, H.-D. Maennling, J. Prochazka, P. Karvankova (Technische Universität Munchen, Germany) After the publication of our generic concept for the design of superhard nanocomposites, (Appl. Phys. Lett. 66(1995)2640; Thin Solid Films 268(1995)64), many papers were published with the aim to deposit, by a variety of techniques, such as plasma induced CVD, reactive sputtering, vacuum arc evaporation and hybrid processing superhard nanocomposites. Whereas in the Ti-B-N system hardness in excess of 40 GPa seems to be relatively easy to achieve, the binary system nc-TiN/a-Si₃N₄ (and also other hard transition metal nitrides instead of TiN) appears more difficult. Based on our earlier work as well as on very recent results that were not published yet, we shall try to elucidate the reasons for the poor reproducibility of our results. Three possible reasons, that appear to be the most frequent for the lack of success, will be discussed in detail: Conditions that have to be met in order to facilitate the thermodynamic requirements for phase segregation, kinetic constrains and the problem of impurities where oxygen seems to have the strongest effect on the degradation of the hardness. It will be shown that only when the oxygen impurity content is less than 0.1 at. % hardness of 45 GPa or more can be achieved. > Finally, I shall briefly discuss the issue of long-term stability of the coatings in view of recent reports of other researchers according to which, for example the (TiAl)N coatings decompose and soften after about half a year exposure to air at room temperature.
11:10 AM		B8-1-9 Quaternary Hard Nanocomposite TiCN/SiCN Coatings Prepared by PECVD P. Jedrzejowski, J.E. Klemberg-Sapieha, L. Martinu (Ecole Polytechnique de Montreal, Canada) Individual hard thin film materials such as TiN, SiN_1.3, SiC and CN_x exhibit, individually, very attractive mechanical, tribological, optical and electronic properties related to their microstructure and chemical bonding. In the present work we combine their characteristics while systematically studying quaternary thin films prepared by PECVD from TiCl₄/SiH₄/N₂/CH₄ mixtures with different concentrations of CH₄. Detailed structural and chemical characterizations using SEM, TEM, XRD, AFM, XPS, and ERD suggest formation of TiCN/SiCN nanocomposite structure. Depth-sensing indentation, nanotribology and curvature measurements, on samples prepared under optimal conditions, reveal a hardness of 56 GPa, Young's modulus of 300 GPa, wear coefficient of 12*10^-6 mm³/Nm, a compressive stress of 2.5 GPa, and an elastic rebound of more than 80 %. The optical constants, color and electrical properties were quantitatively assessed using spectroscopic ellipsometry and spectrophotometry. The optical response of the coatings was best modeled by free electron Drude approach mixed with Lorentz interband absorption. It allowed us to evaluate the film electrical characteristics and compare it with the direct four-point probe resistivity measurements. We compare the properties of the present TiCN/SiCN coatings with the performance of PECVD films from our earlier studies.^a,b,c This includes TiN/SiN_1.3 nanocomposites and SiCN covalently bonded materials, for which we obtained hardness of 43 GPa and 33 GPa, and Young's modulus of 350 GPa and 200 GPa, respectively. ^a. Jedrzejowski, J.E. Klemberg-Sapieha, L. Martinu, Thin Solid Films 426 (2003) 150 ^b P. Jedrzejowski, J. Cizek, A. Amassian, J.E. Klemberg-Sapieha, J. Vlcek, L. Martinu, Thin Solid Films (2003), accepted ^c P. Jedrzejowski, B. Baloukas, J.E. Klemberg-Sapieha, L. Martinu, J. Vac. Sci. Technol. (2003), submitted.
11:30 AM		B8-1-10 Nanoscale Layered Hard Thin Films Deposited by Cathodic Arc Evaporation. Part 1 : Deposition, Morphology and Microstructure C. Ducros, F. Sanchette (CEA Grenoble, France) TiN-(Al,Ti)N ; TiN-CrN and CrN-(Al,Ti)N multilayer coatings have been deposited by the cathodic arc evaporation technique. The period is in the range 7 to 200 nm for a total thickness of 3 mm. The periods control of the nanoscaled hard films is achieved, a priori, by way of a simple geometrical calculation and, a posteriori, via both X-ray diffraction and transmission electron microscopy on cross-sections. Microstructure of the as-deposited coatings has been investigated by means of Xray diffraction and transmission electron microscopy in connection with the decrease of the period. For higher periods (multilayered coatings), the fcc structures which derive from each nitride are observed while only the superlattice structure is found for nanoscale layered films (nanolayered coatings). Microstructure evolution with the period is investigated for the three systems and the differences are comment. Mechanical properties and cutting performances of these hard coatings are described in [1]. [1] C. Ducros, F. Sanchette, Nanoscale layered hard thin films deposited by cathodic arc evaporation. Part 2 : Mechanical properties and cutting performances.
11:50 AM		B8-1-11 Nanoscale Layered Hard Thin Films Deposited by Cathodic Arc Evaporation. Part 2 : Mechanical Properties and Cutting Performances C. Ducros, F. Sanchette (CEA Grenoble, France) Nickel based alloys are difficult-to-machine materials because of their very good mechanical resistance even at high temperature. Cemented carbide cutting tools, widely used for turning these alloys are mainly coated in order to increase their cutting life time. In this study, three compositions of multilayer coating are deposited on turning tools: CrN-TiN, TiN-(Al,Ti)N and CrN-(Al,Ti)N [1]. Mechanical properties were first correlated to the period of these coatings, the period being the thickness of two successive nanolayers. In a second time, the influence of the period on turning performances of such coated cutting tools was studied. The relationship between mechanical properties of coatings and cutting performances is also discussed. Mechanical and tribological properties which strongly depend on coating structure [1], were the best for 7nm period coatings with superlattice structure. These hard coatings allowed a lowering of main cutting force and flank wear during Inconel 718 turning, particularly when (Al,Ti)N is used. Time life of superlattice TiN-(Al,Ti)N coated cutting tool is increased comparatively to CVD coated and (Al,Ti)N coated inserts actually used for machining Inconel 718. [1] C. Ducros, C. Cayron, F. Sanchette, Nanoscale layered hard thin films deposited by cathodic arc evaporation. Part 1 : Deposition, Morphology and Microstructure.