ICMCTF2011 Session B2-2: CVD Coatings and Technologies

Monday, May 2, 2011 1:30 PM in Room Royal Palm 1-3
Monday Afternoon

Time Period MoA2 Sessions | Abstract Timeline | Topic B Sessions | Time Periods | Topics | ICMCTF2011 Schedule

Start Invited? Item
1:30 PM Invited B2-2-1 High-Speed Coating of α-Al2O3 Film by Laser Chemical Vapor Deposition on Cutting Tools
Takashi Goto (Tohoku University, Japan)

WC-Co composite has been widely employed to cutting tools due to high hardness and ductility; however, W is a rare resource and localized on earth. Therefore, alternate material should be sought to substitute W. Since Ti is more abundant and Ti-based compounds have high hardness and strength, TiN-Ni cermet can be a promising cutting tool material having competitive performance of WC-Co composite. The surface of these cutting tools should be generally coated by thermally insulative and anti-abrasive α-Al2O3film, preventing temperature increase and degradation of mechanical properties of substrate material. α-Al2O3 film has been commonly prepared by chemical vapor deposition (CVD) on cutting tools using halide precursors, typically AlCl3, at more than 1300K. Metalorganic CVD (MOCVD) is also applicable to prepare Al2O3; however amorphous or γ- Al2O3 has likely been formed even around 1300K. In order to prepare α-Al2O3 film on TiN-Ni cermets, a low temperature deposition of α-Al2O3 and a high deposition rate are key issues for practical application of TiN-based cermet cutting tools.

We have employed laser CVD (LCVD) using triacetyl-acetoanate-aluminum (Al(acac)3) as Al source gas with two lasers, i.e., Nd:YAG and diode (InGaAlAs) lasers. In the case of Nd:YAG laser, the crystal phase changed from γ to α/γ mixture to α type with increasing deposition temperature (Tdep) and laser power. α-Al2O3 film was prepared at 1214K. The preferred orientation of α-Al2O3 film changed from non-orientation to (104) to (104)/(006) mixed orientation with increasing deposition temperature and laser power. (104) oriented α-Al2O3 film had well-developed facetted grains. The cross-section showed a columnar microstructure suggesting nanometer-sized pores contained in the film. The high energy laser, i.e., diode laser, was more effective to prepare well-oriented α-Al2O3 films at farther lower deposition temperature. At 795K, amorphous Al2O3 film was obtained, while at more than 893K, α-Al2O3 film was obtained. At 110 W and around 950K, significantly (006) oriented Al2O3 film was obtained. The (006) oriented α-Al2O3 films exhibited hexagonal grains about several μm in size. With increasing laser power and deposition temperature, (104)/(012) oriented α-Al2O3 films were prepared. The preferred orientation was also strongly dependent on total pressure, and (104) and (012) orientations showed maxima at 0.2-0.4kPa and 0.2-0.6kPa, respectively. The highest deposition rates of α-Al2O3 film by laser CVDs were 310-324 µm/h which were more than 100 times greater than that of common conventional thermal CVD.
2:10 PM B2-2-3 Protective Aluminum Oxide Coatings on Titanium Alloys from Al Metal-Organic Chemical Vapor Deposition
Yannick Balcaen, Nicoleta Radutoiu (Université de Toulouse, INPT/ENIT, LGP, France); Diane Samelor (Université de Toulouse, CIRIMAT/INPT/CNRS, France); Joel Alexis, Loic Lacroix, Jean-Denis Beguin (Université de Toulouse, INPT/ENIT, LGP, France); Alain Gleizes, Constantin Valhas (Université de Toulouse, CIRIMAT/INPT/CNRS, France)

Alumina coatings present great technological interest in numerous application domains, such as microelectronics, catalysis or surface protection. This study focuses on the implementation of different aluminum oxide coatings processed by metal-organic chemical vapor deposition from aluminum tri-isopropoxide on commercial TA6V titanium alloy to improve its high temperature corrosion resistance. Previous work allowed establishing processing conditions – microstructure relationships for such coatings. Films grown at 350°C and at 480°C are amorphous coatings and correspond to the formulas AlOOH, and Al2O3, respectively. Those deposited at 700°C contain g- Al2O3 nanocrystals. Their mechanical properties and adhesion to the substrates were investigated by indentation, scratch and micro tensile tests. Hardness and stiffness of the films decrease with increasing the deposition temperature and reach a plateau corresponding to the onset temperature crystallization of their crystallization (700°C). The hardness of the coatings prepared at 350°C, 480°C and 700°C is 5.8 ± 0.7 GPa, 10.8 ± 0.8 GPa and 1.1 ± 0.4 GPa, respectively. Their stiffness is 92 ± 8 GPa (350°C), 155 ± 6 GPa (480°C), and 11.5 ± 2.8 GPa (700°C). Scratch tests cause adhesive failures on the films grown at 350 °C and 480°C whereas cohesive failure is observed for the nanocrystalline one, grown at 700°C. Micro tensile tests show a more progressive cracking on the latter films than on the amorphous ones. Similar micro tensile tests were performed for Al oxide coated and uncoated Ti alloy substrates after corrosion with NaCl deposit during 100 h at 450°C. The coated samples have a mechanical strength similar to that of the as processed uncoated samples not corroded. After corrosion test, the mechanical strength of the coated Ti alloys is higher than that of the uncoated alloys. It is concluded that the films allow maintaining the good mechanical properties in the targeted operating conditions. However, after corrosion test only the film deposited at 700°C yields an elongation at break comparable to that of the as processed samples without corrosion. The other coatings do not allow the fall of ductility recorded after corrosion test on TA6V. As a conclusion; the as established processing – structure – properties relation paves the way to engineer MOCVD aluminium oxide complex coatings which meet the specifications of the high temperature corrosion protection of titanium alloys with regard to the targeted applications.

2:30 PM B2-2-4 Thermal Stability and Cutting Performance of Ti or Zr-Doped κ-Al2O3 Coatings by CVD
Masaki Okude, Kohei Tomita, Eiji Nakamura, Akira Osada (Mitsubishi Materials Corporation, Japan)

Al2O3 coatings have been one of the most important coatings for the cutting tools. Al2O3, which maintains high hardness and excellent oxidation resistance under such a severe cutting condition, is that dominate the tool-life. Al2O3 has a several different crystal system, metastable κ phase and stable α phase Al2O3 have been used for the cutting tool. A lot of researches have been done about the heat transformation of κ→α phase. Recently, reported that B- and Ti-B-doped κ-Al2O3 slowly phase transformed to α-Al2O3 than non-doped one, however, investigation into the heat transformation mechanism of κ→α phase on B- and Ti-B-doped κ-Al2O3 has yet been successful.

In this paper, Ti or Zr-doped κ-Al2O3 coatings were deposited using a hot wall CVD equipment, with AlCl3-ZrCl4 or TiCl4-CO2-HCl-H2 gas mixture. After being heated these Al2O3 coatings at several heat-treatment processes, crystal system and morphology of these Al2O3 coatings were analyzed. Heat transformation mechanism of Ti or Zr-doped κ-Al2O3 will be discussed.

2:50 PM B2-2-5 Microstructure and Wear Characteristics of Texture Controlled CVD a -Al2O3 and MT-CVD Ti(C,N) Layers during Steel Machining
Rachid M'Saoubi, Oscar Alm, Tommy Larsson, Mats Johansson, Sakari Ruppi (Seco Tools AB Fagersta, Sweden)

The microstructure and wear properties of CVD α -Al2O3 layers with (10-12) and (0001) growth textures were compared with MTCVD Ti(C,N) layers in single point turning of AISI 4140 steel. The experimental coatings were investigated by FEG-SEM, EBSD and a combination of FIB and analytical TEM techniques prior to and after machining. Substantial texture effects on wear performance of the α -Al2O3 layers were observed. When compared to (10-12) textured layer, an enhanced ability of the (0001) textured layer to undergo plastic deformation was confirmed. The deformation was localised in the near surface region of the layer. In contrast to the α -Al2O3 layers, the Ti(C,N) layer exhibited a more uniform plastic deformation across the entire layer thickness. The wear characteristics of the layers are further interpreted in the light of thermal, mechanical and frictional conditions occurring at the tool–chip contact interface.

3:10 PM B2-2-6 Effect of the N/Al Ratio in the Gas Phase at Constant Supersaturation on AlN Epitaxy on Sapphire by HTCVD
Nour Elhouda Baccar (Grenoble-INP, France); Raphael Boichoit, Elisabeth Blanquet, Michel Pons (SIMAP, France)

Aluminum Nitride (AlN) is a III-V wide band gap semiconductor material with a high thermal conductivity and good chemical inertia. These properties make it suitable for several applications in the opto-electronic field, the most important is the fabrication of UV diodes. Thick AlN layers have been processed by HTCVD (High Temperature Chemical Vapor Deposition) using AlCl3 and NH3 diluted in H2.

The thermodynamic and kinetic modeling of AlN growth on AlN templates at different temperatures and N/Al ratios have been made in previous studies [1-2]. The conclusion of (Boichot and al. [1]) was that experiments should be conducted at constant supersaturation and thickness to understand the actual influence of N/Al ratio on AlN layer quality. The relationship between temperature and supersaturation was established by (Claudel and al. [2]).

In the first part of the study, experiments were performed on graphite substrates to study the preferential orientation of AlN crystals by varying the temperature and N/Al ratio. It is demonstrated that low N/Al ratio allows the control of growth orientation of the AlN crystal facets along the c-axis.

In the second part, experiments were carried out on c-plane sapphire substrates to investigate the effect of supersaturation and N/Al ratio on the morphology of grown layers. The layers are characterized by SEM, XRD, XPS and SIMS to evaluate both crystal quality and O and Cl contamination.

The main conclusion is that the control of surface quality in term of epitaxial relationship between sapphire and h-AlN is possible through a precise setting of supersaturation and N/Al ratio in the gas phase. It is also concluded that epitaxial growth along c-axis is not thermodynamically favored in classical CVD conditions (low pressures, high temperature and N/Al up to 1).

References

[1] R. Boichot, A. Claudel, N. Baccar, A Milet, E. Blanquet, M. Pons, 2010, Epitaxial and pollycristalline growth of AlN by high temperature CVD: Experimental results and simulation, Surface and Coating Technology, article in press.

[2] A. Claudel, E. Blanquet, D. Chaussende, M.Audier, D.Pique, M.Pons, 2009, Thermodynamic and experimental investigations on the growth of thick aluminum nitride layers by high temperature CVD, Journal of Crystal Growth 311, 3371–3379.

3:30 PM B2-2-7 Doped CVD Coatings – Process, Properties and Machine Technology
Hristo Strakov, Renato Bonetti, Audie Scott (Ionbond AG, Switzerland)

The requirements of chemically vapour deposited ( CVD ) coatings for protective application has increased enormously over the past 30 years. The progress from simple monolayer coatings to of today’s complex coating systems were made possible through innovations in coating equipments and the continual optimization of the processes; this in parallel with improved substrate materials, and the progress in preparation periphery, such as pre- and post-treatment operations. A potential for further coating improvement in industrial applications lies with defined structures and new material combinations. One route to obtain better controlled structures is by adding small amounts of metallic or non-metallic elements combined with controlled nucleation for well known processes. This will be illustrated on the example of boron additions to high and moderate temperature Ti-based coatings. The influence of the concentrations of dopants in connection with coating architecture (e.g. multi- or nano-layers) on coating morphology, hardness, friction and wear behavior will be reported.

Application examples of doped coatings and combined coatings will also be presented. Particularities related to diffusion phenomena of the highly mobile boron atom will be discussed.

3:50 PM B2-2-8 CO Addition in Low-Pressure Chemical Vapor Deposition of Medium-Temperature TiCN Based Hard Coatings
Christoph Czettl (Materials Center Leoben Forschung GmbH, Leoben, Austria); Christian Mitterer (Montanuniversität Leoben, Austria); David Rafaja, Uwe Mühle (TU Bergakademie Freiberg, Germany); Stefan Puchner (TU Vienna, Austria); Marianne Penoy, Claude Michotte (CERATIZIT Luxembourg S. à. r. l. , Mamer, Luxembourg); Martin Kathrein (CERATIZIT Austria GmbH, Austria); Herbert Hutter (TU Vienna, Austria)

TiCN/Al2O3 hard coatings grown by chemical vapor deposion (CVD) are state-of-the-art in metal cutting applications using indexable cemented carbide inserts. A TiCN base layer grown by a medium-temperature (MT) CVD process is a crucial feature for wear resistance and toughness of the tools. In order to influence the structure and properties of this base layer, five different MT-TiCN coatings with increasing amounts of CO in the feed gas were deposited using an industrial-scale low-pressure CVD system. The coatings were deposited using a TiCl4-CH3CN-H2-N2-CO feed gas system with a total flux of 60 l/min. The deposition temperature was 900 °C, the deposition pressure 100 mbar. Phase composition, preferred orientation of crystallites and residual stresses were characterized by X-ray diffraction (XRD). Surface topography and fracture cross-sections were investigated by scanning electron microscopy (SEM). Surface roughness was measured using a white light profilometer. Indentation hardness and indentation modulus of the coatings were determined using nanoindentation with a Berkovich indentor. The oxygen content of the different coatings was analyzed by using electron probe microanalysis (EPMA) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). The thickness of the coatings was measured by light optical microscopy (LOM) on polished cross-sections. EPMA and ToF-SIMS measurements confirmed a good correlation between the oxygen amount in the coatings and the CO flow. With increasing CO amount up to 2.2 vol. % in the gas supply, the originally equiaxed grains change to plate-like grains, while the grain size decreases to a few hundred nanometers. Furthermore, the addition of CO makes the preferred orientation of crystallites weaker until it nearly vanishes at 2.2 vol.-% CO in the feed gas. Also the surface roughness decreases with rising CO addition. TEM analyses showed that the incorporation of oxygen leads to a homogenous distribution of voids within the TiCN grains and to increasing density of twin boundaries. The residual stress shows a minimum while hardness and indentation modulus reach a maximum for CO amounts of 1.5 vol.-% in the feed gas.

4:10 PM B2-2-10 Snthesis and Sensitivity by UV Light of SnO2-ZnO Core-Shell Nanowires
Ko-Ying Pan, Han-Chang Shih (National Tsing Hua University, Taiwan); Ming-Hui Chan (Instrument Technology Research Center, Taiwan)
Zinc oxides deposited on Tin dioxide nanowires were successfully synthesized by atomic layer deposition (ALD). The thicknesses of SnO2-ZnO core-shell nanowires are 80, 88, 95, and 100 nm at different ALD cycles: 50, 100, 150, and 200, respectively. The result of electricity measurements shows that the resistance of SnO2-ZnO core-shell nanowires (ALD: 200cycles) is 925Ω, which is much lower than pure SnO2 nanowires (3.6×106Ω). The explanation of this phenomenon is: when electricity passes through SnO2-ZnO core-shell nanowires, the SnO2-ZnO core-shell wires might have a strain at interfaces to keep their shapes complete. Therefore, the energy gap of SnO2-ZnO core-shell wires might decrease, and the electricity will be increased. The result of UV light test shows the recovery time of SnO2-ZnO core-shell nanowires (ALD: 200cycles) is 1030 seconds, which is lower than pure SnO2 nanowires (1827 seconds). SnO2 and ZnO adsorb oxygen easily to form oxygen vacancies on surfaces. The reason of this phenomenon is: when UV light is off, two depletion regions of SnO2-ZnO core-shell wires might produce an effect to cut recovery time down.
4:30 PM B2-2-11 Optical and NO Gas Sensing Properties of GaN/Ga2O3 Zigzag Nanowires
Li-Wei Chang, Jien-Wei Yeh, Han-Chang Shih (National Tsing Hua University, Taiwan)
In this study, we report on the fabrication of GaN/Ga2O3 zigzag nanowires via a chemical vapor deposition system with different ratio of NH3/Ar atmosphere. X-ray, SEM, and High-resolution TEM analyses confirmed that the GaN/Ga2O3 zigzag nanowires have a single-crystal hexagonal structure with axis [101] alignment. The optical properties of GaN/Ga2O3 zigzag nanowires from catholuminescence (CL) and UV-visible absorption spectra show that blue, green, and red emissions because of N-doped process and red-shifts on the band-gap. For application of NO gas sensor, GaN/Ga2O3 zigzag nanowires exhibit drift in their recovery characteristics and for sequential detection of NO gas in the range of 300-400 ppm.
4:50 PM B2-2-12 Equilibrium Segregation of Graphene on Polycrystalline Ni Surfaces by Chemical Vapor Deposition
Chan-Jung Hsu, Pramoda Nayak (National Cheng Kung University, Taiwan); James Sung (KINIK Company, Taiwan); Sheng-Chang Wang (Southern Taiwan University, Taiwan); Jow-Lay Huang (National Cheng Kung University, Taiwan)

Few-layer graphene sheets were prepared on polycrystalline nickel flakes by chemical vapor deposition using equilibrium segregation at a temperature of 800 oC with a very slow cooling rate. The properties of graphene sheets as a function of the hydrogen flow rate were investigated at a constant (CH4 : Ar) flow. It was observed that equilibrium segregation and an optimum gas mixing ratio (CH4/H2 = 0.6/10) are required to synthesize highly crystalline few-layer graphene. The effect of recrystalline treatment of the poly-Ni substrate on the quality of the graphene sheets was investigated. Scanning and transmission electron microscopy and micro-Raman spectroscopy were used to characterize the properties of few-layer graphene. Observations of graphene samples with various recrystalization treatments of the nickel substrate indicate that the defect source on the graphene surface is carbon nanotubes embedded with carbon nanoparticles. The number of graphene layers was estimated based on microscopic observations. The proposed method of growing high-quality large-area graphene provides information on the growth mechanism of graphene and facilitates its controllable synthesis and applications.

Time Period MoA2 Sessions | Abstract Timeline | Topic B Sessions | Time Periods | Topics | ICMCTF2011 Schedule