Papers

ICMCTF2005 Session B6: Plasma Assisted CVD, Thermochemical Treatments and Duplex Technology

Thursday, May 5, 2005 1:30 PM in Room Sunset

Thursday Afternoon

Start	Invited?	Item
1:30 PM		B6-1 Effect of Reactor Geometry on the PECVD Deposited SiO₂ Films A.M. Mahajan, D.K. Gautam (North Maharshtra University, India) Home made Plasma Enhanced Chemical Vapor Deposition (PECVD) system have been used to deposit Silicon dioxide (SiO₂) films. The liquid tetraethoxysilane (TEOS) has been used as a source of Si instead of SiH4 to avoid dangerous handling of SiH₄. The properties viz-uniform thickness within the substrate and substrate-to-substrate, precisely controlled refractive index, low tensile stress, good stoichiometry and surface morphology etc. have been studied using different characterization techniques like ellipsometery, Fourier Transform Infrared (FTIR) spectroscopy, Scanning Electron Microscopy (SEM). In this paper, we intend to report the effect of reactor geometry (i.e. by varying interelectrode spacing) on the properties of the deposited SiO₂ films by keeping the other process parameters at their optimized constant values. Ellipsometer (Philips SD1000) has been used to determine thickness, refractive index and film stress. Through FTIR (Shimadzu-8400) spectroscopy, the characteristic peaks of Si-O-Si stretching, bending and rocking have been indicated with the significant intensities in the spectras taken for the SiO₂ films.
1:50 PM		B6-2 Tantalum-Carbide Layers and Micro-Composite Material Produced by Duplex Plasma and Thermal Treatments A. Raveh (NRC-Negev, Israel); J.E. Klemberg-Sapieha, L. Martinu (Ecole Polytechnique de Montreal, Canada) Tantalum carbides (Ta₂C-TaC) have great potential as an alternative to tantalum in environments requiring high thermal stability and corrosion resistance. In this study, carburized tantalum layers were produced in an inductively coupled radio-frequency plasma using CH₄-H₂-Ar mixtures. The carburizing process was followed by a two-step heat treatment consisting of forming a solid solution and aging, in order to produce a tantalum-carbon micro-composite material (MCM). The carbide phases, the microstructure and the composition of the carburized layers and of the MCMs were characterized by XRD, AES, SEM/EDS, AFM and TPD (temperature-programmed desorption) using mass spectrometry. The mechanical properties of the carburized layers and of the MCMs were studied by laterally resolved depth-sensing indentation and micro-scratch techniques, and the corrosion resistance was examined by impedance analysis. Within the same treatment time, it was observed that the thickness and the phase content (Ta₂C or TaC) of the carburized layer were different for three distinct ranges of fabrication conditions in terms of pressure (p) and radio-frequency power (P). (a) p < 30 Torr, P < 1000 W: a layer 1 µm is formed, exhibiting a steep diffusion profile; (b) 40 < p < 60 Torr, 1400 < P < 1600 W: a thick carbide layer (several microns) is formed, mainly consisting of TaC with a uniform chemical composition and the highest hardness (Hv ~ 25 GPa); and (c) p ~ 100 Torr, P ~ 2000 W: carbon film is formed. During the heat treatment, recrystallization takes place. The size and hardness of the grains and the carbide boundaries were found to be strongly related to the composition and the thickness of the initially carburized layer.
2:10 PM		B6-3 Growth of Non-Regular CN_x Cluster Arrays on Pulse Plasma Nitrided Hot Work Steel Samples M. Zlatanovic (Faculty of Electrical Engineering, Serbia); N. Popovic, Z. Bogdanov (Nuclear Science Institute Vinca, Belgrade) The samples made of hot work steel grade H13 were pulse plasma nitrided in hydrogen nitrogen mixture and post nitrocarburized in carbon containing discharge. Microhardness measurements, optical microscopy, SEM, Raman and XRD analyses revealed the existence of a thin epsilon compound zone onto 150 micrometers thick diffusion layer after plasma nitriding, while a dense 3 micrometers thick carbonitride overcoating was grown during plasma post processing in carbon containing atmosphere. On the surface of plasma deposited hydrogenated carbonitride films intended for tribological applications non-regular "arrays" of different size conductive clusters were found. Similar arrays architecture, when obtained intentionally, can be used for the resonant optical connections in nano and macro optics. Some coupled arrays like the fiberoptic waveides in fiber optics interferometers were also observed. Computer simulation showed that in the case of spherical Al clusters deposited onto dielectric substrate the resonant interaction of light beam with coupled arrays is possible resembling to the light beam splitter on nano scale.
2:30 PM		B6-4 Investigation of Mechanical Properties of TiN-MoS_x Coating on Plasma Nitrided Subtrate M. Rahman, J. Haider, M.S.J. Hashmi (NCPST and MPRC, Ireland) To meet the increased demand from a coating substrate system, it is desirable to use a substrate with higher load bearing capacity and a surface coating with low friction combined with improved wear characteristics. In the present work, the effects of duplex treatment consisting of plasma nitriding and TiN+MoS_x coatings with and without graded interlayer on the mechanical properties of stainless steel substrate were investigated. Plasma nitriding were performed with a new process (Saddle field neutral fast atom beam source) and coatings were deposited by Close Field Unbalanced Magnetron Sputtering (CFUBMS). EDX, Microhardness tester, Rockwell C indenter and X-ray diffraction (XRD) were used to evaluate coating composition and graded profile, micro hardness, adhesion strength and structural properties respectively. These properties were correlated with the tribological properties evaluated by pin on disk test. It was found that duplex plasma nitriding coating exhibited overall enhanced mechanical properties compare to other combination.
2:50 PM		B6-5 Growth Kinetics of Nitride Layers During Microwave Post-Discharge Nitriding F. Castillo (ITESM-CEM, Mexico); J.L. Bernal (ITESM-TOL, Mexico); J. Oseguera (ITESM, Mexico); A. Fraguela (Benemerita Universidad de Puebla, Mexico) Pure iron pieces were nitrided by a post-discharge microwave assisted process. Experimental data during growth of ε and γT layers were used to estimate the nitrogen diffusion coefficient in each phase. The rapid evolution of the nitrogen surface concentration in these processes, allows developing a masse balance model considering thermodynamic equilibrium on surface from the beginning. The mathematical approximate solution of the Fick equation in each layer was obtained taking into account thermodynamic equilibrium in each interface and considering a polynomial representation of the nitrogen concentration for each layer. This involves the statement and study of a moving boundary value problem. A coupled system of ordinary differential equations was solved to estimate. The mathematical results are compared with the experimental data of the nitrogen diffusion coefficient and the nitrogen concentration for each layer.
3:10 PM		B6-6 Fabrication of Iron Nitride Thick Coatings by Reactive RF Plasma Spraying M. Yamada, M. Fukumoto, T. Yasui (Toyohashi University of Technology, Japan) Iron nitride (Fe₄N)is one of the attractive ceramics in respect of its excellent mechanical, electrical and magnetic properties. It might contribute to the various structural components according to form thick coatings. However, there are few studies to fabricate iron nitride thick coatings. Thick coatings can be easily formed by thermal spray process. However, it is difficult to fabricate iron nitride coatings by conventional thermal spray processes. The difficulty is due to decomposition of iron nitride under a high temperature, and the nitride easily transforms into oxide and hereby losing their excellent properties. On the other hand, reactive plasma spraying, in which metal element react with surrounding active species in plasma, has been considered to be an useful process for the fabrication of nitride ceramics thick coatings. In this study, feasibility of fabricating iron nitride thick coatings by reactive RF (Radio Frequency) plasma spraying was investigated. Spraying with Ar/N₂ mixture for plasma gas, Fe/Fe₄N composite coating onto carbon steel substrate was fabricated. The coating obtained was quite thick and dense structure. Thus, it was possible to fabricate Fe/Fe₄N thick coatings by reactive RF plasma spraying. The nitride phase in the coatings was increased with increasing nitrogen gas flow rate in the plasma gas. Furthermore, micro Vickers Hardness of the coatings was also increased with increasing nitrogen gas flow rate. It indicates that increasing of nitride phase in the coatings improved the micro Vickers Hardness. Hereby, it is considered that nitriding reaction of iron is controlled by changing nitrogen gas fraction in the plasma gas.
3:30 PM		B6-7 Structure and Properties of Plasma Nitrided AISI 316 Stainless Steel After Heating Post-Treatments V.H. Baggio-Scheid, G. de Vasconcelos, A.J. Abdalla (Aerospace Technical Center, Brazil) In this work we investigate the structure and properties of plasma nitrided AISI 316 stainless steel after heating post-treatments. The samples were nitrided at 823 K during 3 h. After nitriding, heating post-treatments were made in a vacuum furnace. The influence of the heating time, ranging from 1 up to 16 h, and heating temperature, varying from 732 up to 873 K, on the surface properties was investigated. The samples were characterized using microhardness testing, scanning electron microscopy (SEM), X-ray diffraction (XRD), and roughness measurements. The changes in microstructure, hardness, and length of the diffusion layer were analyzed.
3:50 PM		B6-8 Improvements in the Understanding and Application of Duplex Coating Systems using Arc Plasma Technology J.L. He, K.C. Chen (Feng Chia University, Taiwan) There has been has been interest for some years in the investigation of duplex processes involving plasma nitriding coupled with hard PVD coatings. There are certain problems in the practical application of the technique. One of these relates to the existence of a "black layer", which is believed to be formed in the nitrided layer surface by the nitride decomposition (denitriding) into iron when subjected to the intensified ion bombardment and/or elevated substrate temperature during hard coating. There remain certain unresolved questions, for example: How are the different nitride phases affected? What is the extent of the degradation on the mechanical properties? What is the sensitivity of a specific steel material to the denitriding? (Not to mention the synergetic effect of the substrate softening caused by the elevated substrate temperature). By knowing answers to these questions, it would be possible to control the microstructure of the duplex coatings, the interface of the nitrided layer/hard coating in particular, which would then affect the mechanical properties and the subsequent performance. This paper discusses the keys to the compatibility of duplex coatings, by understanding the interfacial microstructural changes in a nitriding/AIP-TiN duplex system and its mechanical properties. Knowledge of these motivates the evaluation of real service performance of a nitriding/AIP-TiN duplex system for cutting blades by demonstrating this system as applied to optical fiber shears blades and snip blades. The ε-Fe₃N phase with higher nitrogen content, (compared to the α phase and γ´-Fe4N) is proved to be prone to denitriding, over which the black layer formed on SKH 51 steel alloy is thinner than the SKH 2 due to the existence of nitride stabilizer elements in the steel. Regardless of what nitride phases are formed on the prenitrided specimens, the substrate temperature elevation induced by the cathode ion bombardment synergistically enhances the diffusion of nitrogen atoms in the nitriding layer, causing a significant decrease of nitrogen content. The composite surface hardness of the duplex coated specimen is then dominated by the substrate softening effect. This again dominates the adhesion of the TiN layer as revealed by the fact that the adhesion of TiN to ε-Fe₃N is, at all substrate temperatures, higher than adhesion of TiN to the α phase, though the black layer is only formed on ε-Fe3_N phase. The key to the successful duplex coating as revealed by these studies lies in avoiding substrate softening of steel rather than black layer formation. The AIP process allows low temperature deposition of hard coatings which gives considerable prospects for the application of duplex systems to plain carbon and low alloy steels. It therefore promotes the performance of optical fiber shears blades and snip blades made of high carbon steel and low alloy steel, respectively, and specific application examples are presented in the paper.