ICMCTF2008 Session B3-2: CVD Coatings and Technologies

Monday, April 28, 2008 1:30 PM in Room Royal Palm 1-3

Monday Afternoon

Start	Invited?	Item
1:30 PM		B3-2-3 Investigation of the Low Temperature Atmospheric Plasma System for Deposition Photocatalytic TiO₂ Thin Film W.-J. Liu, Y.-L. Lai (I-Shou University, Taiwan) The purpose of this work is to develop a novel low temperature atmospheric pressure (AP) plasma system and use the system to deposit photo-catalytic TiO₂ thin film. In this study, we used titanium isopropoxide (TIP) aqueous solutions as precursors for TiO₂ thin film. The precursor was vaporized by ultrasonic oscillator, and moisture of precursor was introduced into plasma reaction quartz tube by argon carrier gas. The main plasma working gas is argon mixed with O₂. Deposited TiO₂ thin films were investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), Raman spectroscopy. The photocatalytic properties were measured by contact angle and methylene orange decoloration testings. At the same time, the optimum results indicated the parameters of the AP plasma system are the TIP precursors flow rate/oxygen flow rate of 20 sccm/200 sccm for TiO₂ thin film at 500°C, respectively. The relationship between material and optical characteristics of titanium oxide (TiO₂) photo-catalytic films were analyzed in this study. It is found that titanium oxide films possessed more columnar structure and larger specific surface area would result in better photo-catalytic characteristics.
1:50 PM	Invited	B3-2-4 Recent Advances in CVD of α-Al₂O₃ for Tool Coatings S. Ruppi (Seco Tools AB, Sweden) Recent developments in CVD deposition technology have made texture-control of α-Al₂O₃ realistic and feasible on an industrial scale and textured α-Al₂O₃ coatings are attracting increased attention due to the improved wear properties. Consequently, the better understanding of mechanical as well as thermal barrier properties of these kinds of coatings is important. The growth textures of CVD α-Al₂O₃ coatings can be predetermined by optimized nucleation and growth processes. The following textures have been reported for α-Al₂O₃ in the patent literature: (012), (104), (110), (116), (300) and (001). In commercial α-Al₂O₃ coatings the most commonly occurring textures are: (012), and (104). The control of texture from (012) to (014) has resulted in substantial improvement of commercial products. The existence of the (001) texture with promising cutting properties has only recently been reported. This presentation reviews the recent advances in the field of CVD of Al₂O₃. The development of the first generation CVD Al₂O₃ layers with poor coating uniformity and undefined crystal structures to modern α-Al₂O₃ coatings will be described. The latest developments in the area of texture control of α-Al₂O₃ will be treated in more detail. Examples of controlled deposition of (012), (110), (104) and (001) textured alumina layers will be shown. The performances of the textured alumina coatings in metal cutting will be compared and discussed. Results obtained by using XRD, TEM, SEM and practical cutting tests will be presented.
2:30 PM		B3-2-6 CVD-Al₂O₃-Coatings - Correlations Between Structure and Properties M. Höhn, I. Endler (Fraunhofer Institut Keramische Technologien und Systeme (IKTS), Germany); R. Pitonak (Boehlerit, Austria); S. Ruppi (Seco Tools, Sweden); M. Schneider (Mapal, Germany); H. van den Berg, H. Westphal (Kennametal Technologies GmbH, Germany) Today CVD-alumina is one of the most important components in modern coating systems for cutting tools. Commercial alumina coatings can be deposited with different structures. They vary in modification, texture and grain size. A main target in the last years was to get a better knowledge about correlations between texture and wear behaviour of Al₂O₃ layers. In this work different commercial hard metal inserts coated with α- and κ-Al₂O₃ top layers are characterised extensively regarding to structure as well as physical and mechanical properties. At first the alumina layers are analysed concerning their modification, texture and grain size. Following microhardness, Young’s modulus, stress, thermal conductivity and the friction coefficient were determined for each individual structure. It was found that α- and κ-Al₂O₃-layers show distinct differences in microhardness and Young’s modulus. α-Al₂O₃ layers offer Vickers hardness up to 2800 HV[0.01] and Young’s modulus up to 480 GPa while κ-Al₂O₃-layers do not exceed hardness values of 2400 HV[0.01] and Young’s modulus of 370 GPa. Furthermore correlations between grain size and hardness as well as Young’s modulus are received. The lowest thermal conductivity is measured for <104> textured α- and κ-Al₂O₃-layers. All α-Al₂O₃ layers with other textures show a higher thermal conductivity. Based on the structure-property-relations received in this work application advices are given for an optimal application of cutting tools coated with alumina layers of different structures.
2:50 PM		B3-2-7 Improvement of Coating Adhesion by WC Interfacial Layer for Coated Cemented Carbide A.O. Osada, H.H. Homma, E.N. Nakamura, S.T. Tsuchiya (Mitsubishi Materials Corporation, Japan) The effect of WC (Tungsten carbide) interfacial layer on the adhesion strength between a TiCN (Titanium carbonitride) layer and a cemented carbide substrate was investigated. The WC interfacial layer was deposited using a hot-wall CVD (Chemical Vapor Deposition) equipment, with WF₆ - CH₃CN - H₂ - Ar gas mixture. The adhesion strength was evaluated by a turning of alloy steel. The sample with the WC interfacial layer between the substrate and the TiCN layer exhibited a better flaking resistance than the sample without the interfacial layer and the sample with TiN interfacial layer. In order to consider the reasons of the improved adhesion, the crystal orientation relationship between the substrate and WC layer, the diffusion of substrate constituent to the interfacial layer and the residual stress in the TiCN layer were examined.
3:10 PM		B3-2-8 Novel Aluminium-Rich Ti_1-xAl_xN Coatings by LPCVD I. Endler, M. Höhn, M. Herrmann (Fraunhofer Institut Keramische Technologien und Systeme (IKTS), Germany); R. Pitonak (Boehlerit, Austria); S. Ruppi (Seco Tools, Sweden); M. Schneider (Mapal, Germany); H. van den Berg, H. Westphal (Kennametal Technologies GmbH, Germany) Today Ti_1-xAl_xN coatings represent a standard PVD coating for cutting tool applications. Fcc-Ti_1-xAl_xN is a metastable homogeneous phase with excellent properties as high hardness, high oxidation resistance and high cutting performance. An important aim is the preparation of coatings with a maximum aluminium content. The higher the aluminium content the higher the oxidation resistance. But PVD processes are limited to the deposition of monophase Ti_1-xAl_xN coatings with a maximum x = 0.65. Higher x leads to the co-deposition of the softer hexagonal wurtzite phase. In this work the preparation of monophase fcc-Ti_1-xAl_xN coatings with x up to 0.9 is described. A LPCVD process using TiCl₄, AlCl₃, NH₃, H₂, N₂ and Ar is applied. At deposition temperatures between 800°C and 900°C very hard Ti_1-xAl_xN layers with 0.7 < x < 0.9 were prepared. The layers possess a high hardness around 3000 HV and Young’s moduli up to 540 GPa. A strong adherence on hardmetal inserts is achieved by deposition of a thin TiN bonding layer. Scratch test measurements showed critical loads of about 100 N. The stress in the coatings depends on the deposition conditions and varies between 650 MPa and -200 MPa. In different wear tests a high performance of the CVD-Ti_1-xAl_xN was observed. Coated inserts showed a reduced wear by 30% in comparison with a state-of-the-art PVD coating in reaming of steel and cast iron. In milling 42 CrMo4V the new CVD-Ti_1-xAl_xN also exceeds the best PVD coatings available on the market today.
3:30 PM		B3-2-10 Microstructural Investigation of MTCVD Ti(C,N) Coatings S. Canovic (Chalmers University of Technology, Sweden); S. Ruppi (Seco Tools AB, Sweden); M. Halvarsson (Chalmers University of Technology, Sweden) CVD Ti(C,N)/alumina multilayers have been shown to be successful as wear resistant coatings on cemented carbide cutting tools. The alumina layers are generally deposited by conventional CVD, while the intermediate Ti(C,N) layers are deposited by moderate temperature chemical vapour deposition (MTCVD). Previous work has mainly been concentrated on the alumina layers, while this work focuses on the MTCVD Ti(C,N) layers. For conventional CVD of Ti(C,N) the deposition temperature is approximately 1000°C. In MTCVD of Ti(C,N) more reactive organic precursors are used, which facilitates a lower deposition temperature at 700-900°C. Deposition of the investigated MTCVD coatings was carried out in a computer-controlled hot-wall CVD reactor. Commercial cemented carbide inserts with a composition of 94% WC and 6% Co were used as substrates. The Ti(C,N) coatings are 8 µm thick and three dopings are used: CO, CO₂ and AlCl₃. The MTCVD Ti(C,N) coatings were pre-examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD was used to determine the texture coefficients and the SEM was used to study the surface morphology. One part of this work was carried out by transmission electron microscopy (TEM) using a Phillips CM 200 FEG working at 200 kV. Cross-section TEM thin foils were prepared using a combined FIB/SEM (focused ion beam/scanning electron microscope) instrument, whereby electron transparency was achieved throughout the coating thickness. Another part of this work was carried out using Electron Backscattered Diffraction (EBSD) in the SEM. The detailed microstructure and texture of the different coatings will be described in this work.
3:50 PM		B3-2-11 Influence of the Deposition Temperature on Mechanical and Tribological Properties of Si-C:H Coatings on Nitrided and Postoxidized Steel Deposited by DC-PACVD C. Forsich, D. Heim (University of Applied Sciences, Austria); T. Mueller (Rubig GmbH & Co KG Anlagentechnik, Austria) Amorphous carbon-silicon coatings (Si-C:H) combine a series of interesting properties, such as a low friction coefficient, high hardness and wear resistance. Si-C:H films on nitrided steel, especially on construction and on heat treatable steels provide a substantial potential for new applications e.g. such as machine parts. The nitriding can be done with or without white layer. By a postoxidation of the nitrided surface additional corrosion resistance can be achieved. In the present study Si-C:H-films were deposited by means of DC-PACVD using HMDSO and TMS as precursors with deposition temperatures ranging between 190 and 550°C. Prior Si-C:H deposition different plasma-nitriding processes have been performed and some of the samples were also postoxidized. The results show a decreasing deposition rate and an increase of the surface energy at higher deposition temperature. Mechanical properties were studied by a Fischerscope tester whereas the phase composition was determined using XRD. The temperature has a great impact on the hardness. The X-ray analysis shows that the coatings have amorphous structure also at higher deposition temperatures. The evolution of XRD diagrams indicate a stabilization of iron nitride (ε-Fe3N) caused by the present iron oxide phase on postoxidized steel substrates. Further a degradation process of the oxide phase as well as the epsilon phase can be observed with increasing temperature. The investigation of the adhesion of the deposited coatings was evaluated by means of a scratch test method. In addition the tribological properties of the obtained films were assessed with a ball-on-disc test at different humidity conditions.
4:10 PM		B3-2-12 New Methodologies for Enhancing the Nucleation, Growth Rate, and Quality of Nanocrystalline Diamond Films P.J. Heaney, C.D. Torres (University of Wisconsin, Madison); A.V. Sumant (Argonne National Laboratory); A.R. Konicek, M. Hamilton, R.W. Carpick (University of Pennsylvania); F.E. Pfefferkorn (University of Wisconsin, Madison) Diamond has outstanding material qualities such as high hardness, high thermal conductivity, chemical inertness, and extremely low friction and wear under particular conditions. Applying diamond coating to tool surfaces can significantly increase the tribological performance and hence the operational life-span of the tool. However, in case of micro end mills, due to their small size (5-300 µm in diameter) and complicated shapes, obtaining diamond coating is a challenging task. We have developed a new method based on Ar/CH₄/H₂ chemistry using hot filament chemical vapor deposition (HF-CVD) to deposit conformal nanocrystalline diamond thin films on micro-end mills with coating thickness as low as 100 nm, and with sp³ content as high as 95%. The effect of the seeding technique and gas chemistry on the resultant nucleation and growth is characterized using: scanning electron microscopy, atomic force microscopy, and white light interferometry to evaluate coating thickness, growth morphology, and grain size; Raman and near-edge x-ray absorption fine structure spectroscopy (NEXAFS) to characterize the chemical bonding and sp²/sp³ ratio; nanoindentation to evaluate the mechanical properties of the coating; and tribometry to evaluate tribological properties of the film. Machining tests have shown a clear increase in coating performance with the new Ar/CH₄/H₂ based NCD coatings, which are thinner (~100 nm), have smaller grain size and, higher sp³ content than the previous conventional thicker coatings (>600nm), grown based on H₂/CH₄ gas chemistry.