Plasma Assisted CVD, Thermochemical Treatments and Duplex Technology

Friday, May 4, 2001 8:30 AM in Room Golden West

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8:30 AM B7-1-1 Manufacturing and Structure Investigation of Plasma-Enhanced CVD Layer Systems
A. Leonhardt, K. Bartsch, Ch. Taeschner (Institut für Festkörper- und Werkstofforschung Dresden, Germany)
Several kinds of d.c. plasma assisted chemical vapour deposition (PACVD) processes were used to deposit different crystalline and crystalline/amorphous wear resistant layer systems. Especially, this contribution will deals with the deposition and structure investigation of the 3 following systems (a) crystalline Al@sub 2@O@sub 3@-layers consisting of different modifications (a, g, k) in dependence on the deposition temperature, the gas phase composition and the kind of plasma excitation (unipolar or bipolar) (b) a composite layer system existing of an amorphous carbon matrix with homogeneously distributed nanocrystalline TiC-particles (TiC/a-C) using a d.c. pulsed discharge and at a deposition temperature of 763 K (c) a multilayer coating of 2 non-mixing hard materials (TiN and both amorphous and crystalline Al@sub 2@O@sub 3@) and its texture in dependence on the thickness and structure of individual layers. On the basis of these deposited layer systems it can be demonstrated that the plasma assisted chemical vapour deposition is an excellent method for the fabrication of new interesting wear resistant layer systems, which cannot obtained by classical CVD. An extensive investigation of the structure properties of layer systems reveal additionally that special constitutions can be only obtained using the PACVD-process.
9:10 AM B7-1-3 Gas Phase Analysis of TiN and TiC Plasma Enhanced CVD Processes by Molecular Beam Mass Spectrometry
C.M. Reddy, C.C. Amato-Wierda (University of New Hampshire)
Plasma-enhanced chemical vapor deposition (PECVD) is becoming an increasingly attractive process for the hard coatings industry because of its low temperature capabilities. Many thermal CVD processes for refractory coatings, such as TiN and TiC, currently require temperatures from 700°C to over 1000°C, which can be deleterious to steel substrates. Optimization of plasma CVD require an understanding of how process variables affect the gas-phase composition during deposition. This is especially critical for PECVD because it is a complex environment containing neutrals, radicals, and ions. The relative densities of these species and their ion energies can be controlled by process variables. This paper will describe the recent design and construction of a PECVD reactor coupled to a molecular beam mass spectrometer. The plasma reactor contains planar electrodes and uses a capacitively coupled rf plasma. Quadrupole molecular beam mass spectrometry was used for the analysis of the gas phase of the PECVD processes. We will present our results on the gas-phase chemistry of PECVD processes for TiN and TiC. The precursor systems for TiN and TiC are TiCl@sub 4@ + NH@sub 3@ and TiCl@sub 4@ + CH@sub 4@, respectively. The gas-phase species occurring during these processes were determined as a function of process variables, such as: rf power, reactant ratios, reactor pressure, and residence time. Higher plasma power increased the intensity of ions from TiCl@sub 4@ and Ar up until 100 W, from NH@sub 3@ plasma up until 150 W and then ion intensity reached a plateau value with increasing rf power. The Ar ion intensity increases with total reactor pressure up to 200 mTorr and then ion intensity was found to decrease with pressure. Similar trends were observed with ions from NH@sub 3@ plasma as the total reactor pressured increased. Ion energy distribution studies attempted showed that there exists a ion energy range for each species.
9:30 AM B7-1-4 Growth of BON Thin Films Using Low Frequency RF Plasma Enhanced MOCVD and Study on the Deposition Parameter Effects on the Film Hardness
G.C. Chen, M.C. Kim, J.G. Han, S.-B. Lee, J.-H. Boo (Sungkyunkwan University, Korea)
Superhard materials are widely applied in the cutting, polishing and wear protection engineering. The successful synthesis and fabrication of BN and BCN as well as BCO indicates that the materials, composed of boron with other light elements such as nitrogen, carbon and oxygen, are attractive candidate of superhard material. Recently, the possibility of existence of a BON material has been proposed. So far, however, there is no report on the thin film growth and hardness measurement of this material in detail. RF plasma enhanced metalorganic chemical vapor deposition (PEMOCVD) has successfully been applied into the fabrication of oxide, nitride and boron-containing materials. The frequency was usually 13.56 MHz in these cases. The high ratio of gas-phase molecule dissociation was expected by use of such a high frequency that may caused the multi-deposit in fabrication of multi-elements compounds. To avoid this disadvantage, a deposition process with low frequency is h! ighly desirable. In this study, therefore, a PEMOCVD derived by 100 KHz RF was used to grow this new material, BON, with trimethylborate precursor as boron and oxygen source. The plasma source gases were Ar and H@sub 2@. Two kinds of reactive gases (N@sub 2@ and NH@sub 3@) were employed as the nitrogen source. The as-grown films were characterized by XPS, RBS, FTIR, UV, SEM and Knoop microhardness tester. The effects of deposition parameters such as reactive gases, substrate temperature and deposition time on the hardness of film were investigated. Based on the experimental results, we could get the conclusions as followings: (1) BON films can be more rapidly grown using the NH@sub 3@ rather than N@sub 2@; (2) The hardness of BON films gained with N@sub 2@ was higher than that of NH@sub 3@; (3) The higher substrate temperature the higher hardness; (4) Both structure and composition of the as-grown films can influence the film's hardness. The film with smooth and continuous s! tructures as well as with high N-content possessed high hardness.
9:50 AM B7-1-5 Electrolytic Plasma Processing for Cleaning and Metal-Coating of Steel Surfaces
X. Nie, F.L. Wang (Louisiana State University); E.I. Meletis (Lousiana State University)
Electrolytic plasma processing (EPP) involves electrolysis and electrical discharge phenomena and consists an emerging, environmentally friendly surface engineering technology. Electro-plasma/material surface interactions during processing can be used for cleaning of metal surfaces, formation of diffusion layers and/or deposition of metal, ceramic and composite coatings. This work is concerned with cleaning and deposition of metal coatings on steel surfaces for corrosion protection. The effects of process parameters on cleaning steel surfaces from oxides were first investigated. Surface roughness and oxygen content before and after cleaning were evaluated by profilometry and energy dispersive spectroscopy (EDS). The structure of the "cleaned" outer surface layer as it develops after the electro-plasma interaction was studied by high resolution TEM. Mechanically cleaned surfaces (shot blasting) were also evaluated for comparison purposes. EPP was also utilized to deposit Zn and Al-Zn coatings on cleaned surfaces using a variety of process parameters. Morphology and microstructure of the coatings were studied using SEM. Coating adhesion as a function of surface roughness and hardness was assessed by conducting pull testing and hardness measurements, respectively. The results show that EPP can effectively produce clean surfaces and metal and alloy coatings and has a great potential as a new plasma surface engineering technique. Key words: Atmosphere plasma, plasma electrolysis, Cleaning, Zn coating, Zn-Al coating .
10:10 AM B7-1-6 Plasma Nitriding of Austenitic Stainless Steels: Formation, Structure and Properties of Surface Layers
E. Menthe (DaimlerChrysler AG, Germany)
This contribution presents an overview of Plasma nitriding of austenitic stainless steels. Austenitic stainless steels are often used as construction materials in the chemical and food processing industries. While the corrosion resistance of these materials is excellent, their hardness and wear resistance is relatively low. Many attempts have therefore been made to increase the wear resistance without deteriorating the corrosion resistance. Beginning in the late 80`s it has been shown by different research groups that plasma nitriding at temperatures at or below 450°C offers the opportunity to enhance the mechanical properties of austenitic stainless steels without affecting the excellent corrosion resistance. In this case a metastable phase named S-Phase or saturated austenite with outstanding properties is formed. Inside this new phase the Nitrogen remains in solid solution instead of removing Chromium from the austenitic structure by precipitation of CrN. This type of layer can also be produced by other surface treatments, i.e. plasma immersion ion implantation, ion beam nitriding, ion implantation or by a PVD coating. In this paper, the formation, the structure and the properties of the surface layers formed at temperatures ranging from 300°C to 500°C are described. In particular the influence of treatment gas, glow discharge parameters, substrate material, treatment temperature and time on the formation and the microstructure will be highlighted. This will be followed by the presentation of the mechanical properties i.e. hardness, adhesion, wear and corrosion resistance and fatigue life. The surface layer has been analysed directly after plasma nitriding as well as in the depth profile. Finally these results are compared to the results obtained by other nitriding treatments.
10:50 AM B7-1-8 Comparison Between Microwave Plasma and PI3 Nitriding of Aluminum.
F. Rossi (European Commission, Joint Research Centre, Italy); K. Spyradek Hahn (Forschung Zentrum Seibersdorf, Austria); R. Sonnleitner (Forschung Zentrum Seiberdorf, Austria)
Nitriding of Al alloys has been performed with microwave plasma and PI3. The parametric study illustrates the influence of gas composition,temperature, ion flux and energy of the impinging species. TEM study oif the nitrided layers shows the formation of AlN. The condition of formation of AlN depends strongly on temperature which imposes the diffusion of Al and N as well as resputtering of the modified layer.
11:10 AM B7-1-9 A Study on the Cavitation Resistance of Ion Nitrided Steel
K.C. Chen, J.H. He, W.H. Huang (Feng Chia University, Taiwan)
Cavitation is a common deterioration process of a material resulting from high-speed fluid attack. Surface treatments are usually preferably considered to promote cavitation resistance because of economic reasons and longer durability performances. The cavitation behaviours of ion nitrided carbon steel, the response of nitriding layer to various cavitation environments, in particular were studied. An ASTM G32-85 standard method was conducted to proceed cavitation test in fresh water, 3.5wt% NaCl, and 3.5wt% HCl aqueous electrolyte, respectively. Experimental results show that nitriding of steel would reduce the cavitation rate of the S48C steel in fresh water. This is due to the hard-nitrided surface that can resist mechanical damage. Electrochemical corrosion plays a part in the case of 3.5wt% NaCl and 3.5wt% HCl electrolyte. Ion nitrided specimens in the 3.5wt% NaCl electrolyte therefore show higher cavitation weight loss than that in fresh water. However, the nitriding layer decreases cavitation rate of the nitrided steel. Ion nitrided specimen in the 3.5wt% HCl electrolyte subjecting primarily for electrochemical attack to the nitriding layer shows inferior cavitation resistance than blank steel. This can be proved by the polarization test, for which the nitrided steel has higher corrosion current than blank steel. Therefore, the method of surface modification should be properly determined depending on what electrolyte would be used. Ion nitriding of carbon steel in our case is suitable for fresh water and 3.5wt% NaCl electrolyte, but not for 3.5wt% HCl electrolyte.