ICMCTF2005 Session B7-2: Properties And Characterization of Hard Coatings And Surfaces

Monday, May 2, 2005 1:30 PM in Room Golden West

Monday Afternoon

Start	Invited?	Item
1:30 PM	Invited	B7-2-1 Designed Coatings: Correlation of Coating Properties to Application Results W. Kalss, V.H. Derflinger, J.L. Endrino, C. Gey (Balzers AG, Liechtenstein) More than 25 years ago TiN has started the success story of PVD coated cutting tools. In the meantime TiAlN and AlCrN based coatings dominate the market. However, new outstanding coating solutions with short innovation cycles are needed to fulfill the requirements of the cutting tool market. Reduced development time can only be achieved by an in depth knowledge of the correlation of coating properties (mechanical, thermal) to cutting tool applications, without using time consuming application tests. Based on milling applications in Tool Steel, Hardened Tool Steel and CK 45 the requirements for coatings are derived. A correlation of cutting tests with coating properties of industrial Ti_1-x Al_xN based coatings and recently introduced Al_xCr_1-xN coatings has shown that key properties as abrasive wear resistance, hot hardness and oxidation resistance can be used to predict coating performance. It is also shown that in the future additional focus of university research has to be given to develop advanced methods for measurement of coating properties at application temperatures.
2:10 PM		B7-2-3 Effect of Film Thickness and Ti Interlayer on the Structure and Properties of Nanocrystalline TiN Thin Film Deposited by Unbalanced Magnetron Sputtering J.-H. Huang, F.-Y. Ouyang, G.-P. Yu (National Tsing Hua University, Taiwan) TiN thin films were deposited on AISI D2 steel substrates using unbalanced magnetron (UBM) sputtering. The objective of this study was to investigate the effect of film thickness and Ti interlayer thickness on the composition, structures, mechanical properties, and corrosion resistance of TiN films. The results showed that (111) was the dominant preferred orientation in the TiN films. The variation of film thickness only slightly affected the N/Ti ratio, roughness, and grain size. The packing factor was almost constant with film thickness and the thinnest specimen (120 nm) reached a quite high packing factor of 0.8. Nanoindentation data, ranging from 21~26 GPa, indicated that hardness of the films was not related to the film texture and film thickness. The residual stresses of all TiN films were compressive, and mostly decreased with increasing film thickness in TiN/D2 specimens. In the bi-layer TiN/Ti coating, there was a critical Ti interlayer thickness (120~150nm) to effectively reduce the thermal stress and residual stress in the TiN coating. The results of potentiodynamic polarization scan in both 5% NaCl and 0.5M H2SO4 + 0.05M KSCN solutions indicated that packing factor was more effective than film thickness to the corrosion resistance for the coating. Furthermore, increasing film thickness or adding a Ti interlayer could effectively protect the substrate from the corrosive medium, if the packing factor was sufficiently high.
2:30 PM		B7-2-4 Residual Stress Development in UMS TiN Coatings M. Bielawski, D. Seo (National Research Council, Canada) TiN coatings produced by the unbalanced magnetron sputtering (UMS) technique were used to study the relationship between the most relevant deposition parameters, such as substrate bias and working gas pressure, and the residual stress level. The test coatings were deposited on thin silicon and steel substrates to allow residual stress measurements using the laser beam profilometry method. Aside from residual stress magnitude, the UMS TiN coatings were also evaluated for microstructure, composition, hardness and Young's modulus. It was found that the properties of TiN coatings could be linked to the residual stress magnitude, which in turn was strongly affected by the deposition process conditions and substrate properties. Significantly higher stresses were observed for coatings deposited on steel substrates. Subsequently, the role of intrinsic and thermal stresses in the coating/substrate system was discussed. In the next step of the experimental program, stress-temperature correlation plots were produced, by subjecting the coatings to temperature cycles from room temperature (RT) to temperatures above the maximum deposition temperature and back to RT. These plots were used to evaluate possibility of residual stress relaxation during the post-deposition heat treatment. A detailed discussion of these results as well as the correlations between deposition parameters, residual stress level and coating properties is provided in the paper.
2:50 PM		B7-2-5 The Effect of Plasma Immersion Ion Implantation on the Hardness and Composition of Cathodic arc deposited Titanium Nitride Thin Films S.H.N Lim, D.G McCulloch (RMIT University, Australia); M.M.M Bilek, D.R. McKenzie, M Swain (University of Sydney, Australia); J. du. Plessis (RMIT University, Australia) Intrinsic stress in coatings strongly influences quality since high stress can cause the film to delaminate. We have investigated ways of controlling the intrinsic stress by combining plasma immersion ion implantation (PIII) with conventional physical vapour deposition. This duplex system combines conventional deposition and periodic pulses of highly energetic ions to implant into the growing film. In this work, we deposit titanium nitride (TiN) thin film coatings using a duplex filtered cathodic arc and PIII system. We systematically vary the pulsing voltage and frequency of the PIII, and then characterized the microstructure using transmission electron microscopy (TEM), indentation hardness using an ultra micro indentation system (UMIS) and x-ray photoelectron spectroscopy (XPS) was used to study the effect of nitrogen flow rate and pulsing voltage on the chemical composition. Our result shows that as we increase the pulsing voltage, the intrinsic stress of the film dramatically decreases. By applying a 2kV pulsing energy, the stress can be reduced by approximately 50% compared to an unbiased coating. TEM shows that as the pulsing voltages increases, the preferred orientation of the crystallites flipped from a {111} to {200}. Increasing the implantation voltage also resulted in a decrease in the indentation hardness. This observation is explained using a model correlating the level of intrinsic stress with the measured indentation hardness. Samples using XPS were specifically selected to study the effect of flow rate of nitrogen, the pulsing energy and the frequency of the high voltage pulse.
3:10 PM		B7-2-6 Structural and Chemical Properties of Sputtering Deposited Ti-Ge-N Thin Films C.S. Sandu (IPMC-SB-EPFL, Switzerland); R. Sanjines (SB-EPFL, Switzerland); M. Benkahoul, M Parlinska-Wojtan (IPMC-SB-EPFL, Switzerland); A. Karimi (EPFL, Switzerland); F. Levy (IPMC-SB-EPFL, Switzerland) Thin films of TM-Si-N (TM = early transition metal) are used as protective coatings. The most investigated among the ternary composite systems is Ti-Si-N. The system Ti-Ge-N has been chosen to extend the knowledge about the formation of nanocomposite films. Ti-Ge-N and TiN/GeN-multilayer thin films were deposited by reactive magnetron sputtering on Si and WC-Co substrates at Ts= 240°C, from confocal Ti and Ge targets in mixed Ar/N₂ atmosphere. The nitrogen partial pressure and the power on the Ti target were kept constant, while the power on the Ge target was varied in order to obtain various Ge concentrations in the films. The decrease of N content is 2 times faster than the Ge increase in the films. No presence of Ge-N bonds was detected by FTIR absorption spectroscopy. TEM investigations revealed important changes induced by Ge addition in the columnar morphology and structure of Ti-Ge-N films. EELS study revealed a significant increase of Ge content at the grain boundaries. The segregation of Ge atoms on the crystallite surface is responsible for limiting the growth of the crystallites. The nanohardness behavior is explained by the decrease of grain sizes due to Ge addition. TiN/GeN multilayer films with TiN thickness ?? 6 nm and various GeN thicknesses between 0.5 and 4 nm were deposited using target shutters. A nanocrystalline multilayer film is formed, where the suppression of crystal growth is controlled by the successive deposition of two phases. STEM, TEM, nanoindentation and XRD techniques were employed to characterize the multilayer films. The properties of both types of films (monolayer and multilayer) are compared and interpreted.
3:30 PM		B7-2-8 Decomposition of Supersaturated Ti-Al-N P.H. Mayrhofer (University of Leoben, Austria); A. Hörling (Linköping University, Sweden); C. Mitterer (University of Leoben, Austria); L. Hultman (Linköping University, Sweden) Ti-Al-N coatings are well known for their excellent wear resistance enabling improved machining processes like high speed and dry cutting. In the as-deposited state, these coatings show a supersaturated Ti_1-xAl_xN solid solution with NaCl-structure if the Al/Ti at.-ratio is smaller than ~ 2 for arc-deposited thin films. The metastable Ti_1-xAl_xN phase tends to decompose into its stable constituents, face-centered-cubic (fcc) TiN and hexagonal-close-packed (hcp) AlN, due to their limited equilibrium solubility. For understanding the decomposition route, Ti_1-xAl_xN thin films with different chemical composition x = 0, 0.25, 0.5, and 0.66, prepared in an industrial-sized arc-evaporation system, are investigated in detail. Here we show, using differential scanning calorimetry, small-angle neutral scattering, and X-ray diffraction, that after recovery and structural reordering, the fcc-Ti_1-xAl_xN phase starts to decompose at about 800°C during annealing. Fully coherent Al-rich fcc-domains, corresponding to Guinier-Preston zones in precipitation hardening Al-alloys, with a size of 2-3 nm form during the early stage of the decomposition followed by the formation of Ti-rich fcc-domains at about 900°C. Further annealing causes a coarsening of these domains and precipitation into the equilibrium fcc-TiN and hcp-AlN phases. All of these microstructural processes are directly related to changes in the mechanical properties of the thin films. Activation energies for the phase transformations occurring during thermal annealing up to 1400°C are derived by means of Kissinger plots. Considering that the compositions studied are deep within the miscibility gap of the Ti-Al-N system and the observation of gradually increasing compositional gradients, the fcc-Ti_1-xAl_xN phase decomposition is to a large part driven by spinodal decomposition.
3:50 PM		B7-2-9 High Thickness Ti/TiN Multilayer Thin Coatings for Wear Resistant Applications C. Pecchio (Istituto Scientifico Breda S.p.A., Italy); E. Bemporad (University of Rome, Italy); S. De Rossi (Istituto Scientifico Breda S.p.A., Italy); F. Carassiti (University of Rome, Italy) Hard coatings like TiN normally contain a high degree of internal (usually compressive) stress owing to mutual impingement of growing grains, growth defects developed during the deposition process and thermal mismatch effects; it is, therefore, difficult to produce single-layer TiN coatings thicker than 6-7 µm, without encountering adhesion problems on substrate materials. In the present study thick coatings (i.e. >10 µm ) have been achieved by multilayering, in an alternating fashion, Ti and TiN leading to a tougher and less highly stressed film. A set of multilayered Ti/TiN coatings microns were deposited, using an arc reactive PVD, with different Ti/TiN ratios, different layers number and different overall thickness. Mechanical and tribological properties were characterized using nano and micro hardness test, crater grinding test, scratch test, Rockwell test and impact test. Coatings interfaces, surface defects and roughness characterization were made by Digital Optical Microscopy coupled with Image Analysis, SEM-EDS, TEM-EDS, FIB and AFM. Residual stress were investigated by the use of X-ray diffraction microscopy with the sin²φï? method. In spite of their thickness the Ti/TiN multilayer reveal both residual stress and a wear coefficient comparable to thin layers. With a careful tailoring of the relative Ti/TiN thickness and the interfacial transition between the two layer types, a compromise between hardness and toughness can be achieved.Work on thick Ti/TiN multilayered coatings has demonstrated substantial benefits in both abrasive and erosive wear resistance. This improvement has been suggested to be the result of any of the following mechanisms: crack deflection due to weak interfaces, crack-tip shielding by plastic deformation in combination with strong interfaces, favourable gradients in residual stresses and crack deflection due to differences in the elastic moduli of the individual layer materials.