ICMCTF2004 Session B10: Surface Processing and Modeling

Thursday, April 22, 2004 8:30 AM in Room Sunset
Thursday Morning

Time Period ThM Sessions | Abstract Timeline | Topic B Sessions | Time Periods | Topics | ICMCTF2004 Schedule

Start Invited? Item
8:30 AM B10-1 The Interface TiN-Si3N4: a Model for the Bonding in Hard Nanocomposites
J. Patscheider (EMPA, Switzerland); N. Hellgren, R. Haasch, I. Petrov, J.E. Greene (University of Illinois at Urbana-Champaign)
The advent of superhard nanocomposite coatings and their understanding evidenced the importance of atomically sharp interfaces between the nanocrystallites and the surrounding amorphous phase or the properties of these materials. Especially the quality of the interfaces in terms of stoichiometry and completeness of phase separation are decisive for the outstanding properties of nanocomposite hard coatings. However, there is no analytic technique available which could probe the chemical nature of these interfaces due to their three-dimensional nature. To overcome these limitations model interfaces were synthesized on single-crystalline TiN under clean conditions with several monolayers of Si3N4 and other materials relevant for the system TiN-Si3N4. The thickness was chosen to be close to the typical values for hardness-enhanced nanocomposites and to be transparent for photoelectrons from the base material. In situ analyses with XPS were performed in order to analyze the influence of these overlayers on the bonding characteristics. The results and their implications on bonding properties are discussed with respect to macroscopic properties.
8:50 AM B10-2 Modelling Nitrogen Atom Flux in Post-discharge Nitriding Processes
T. Belmonte (INPL-Ecole des Mines, France); C. Jaoul, J.N. Borges (LSGS, France)
Nitriding of pure iron using microwave N2-H2 post-discharges is modelled by coupling hydrodynamic and kinetics of the gas phase, surface processes and solid diffusion. Despite a rigorous physical approach of each step is developed, several assumptions on basic data are necessary to complete the model. However, the description of the interface phenomena provides a clear understanding of the material response to a given gas phase composition. The most important aspect presented deals with the dissolution of nitrogen atoms into the iron nitride ε-Fe2N1-x at the topmost surface of the sample. As chemically adsorbed nitrogen atoms are involved in both the Langmuir-Hinshelwood and the Eley-Rideal loss mechanisms of N atoms into N2, their dissolution implies a subsequent decrease of the loss probability of N atoms at the surface. This is the main reason why post-discharge nitriding works at high temperature. The consumption of the nitrogen atoms at the surface of the sample limits considerably their loss by recombination. Finally, a first comparison with experimental results is also included, showing satisfactory trends.
9:10 AM Invited B10-3 The Influence of Ion Implantation during Reactive Sputtering
D. Depla (Ghent University, Belgium)

The Ion-induced Secondary Electron Emission (ISEE) coefficient depends strongly on the target surface condition and therefore we can retrieve from the target voltage behaviour information about the processes occurring at the target during DC reactive magnetron sputtering. Using this simply technique, the target voltage behaviour for the reactive sputtering system Si/N2/Ar was studied in detail. The target voltage behaviour must be attributed to the presence of non-reacted nitrogen atoms implanted in the target during the reactive sputtering process. A similar effect was notice during DC magnetron sputtering of a silver target in an argon/nitrogen mixture. Also, non-reacted nitrogen atoms were detected in the target surface with in situ XPS during reactive glow discharge sputtering of copper. These experiments gave clear evidence for the important role of reactive ion implantation in the poisoning mechanism during DC magnetron sputtering.

To explain the noticed target voltage behaviour, an analytical model is proposed based on the shallow implantation of reactive gas ions in the target. The chemical reaction between the implanted atoms results in a decrease of the target surface recession speed, and consequently the surface concentration of the implanted species increases, further reducing the recession speed of the target surface, resulting in an avalanche situation when the reactive gas mole fraction in the plasma exceeds a critical value. Besides their reaction with the target atoms, the high concentration of these implanted atoms enhances also the formation of reactive molecules by reaction between two implanted atoms formed by the decomposition of the molecular ions. This second reaction can explain several features of the measured target voltage behaviour. In the case of Al/O2/Ar, a good agreement was found between the results of the above described analytical model and those achieved by TRIDYN simulations.

9:50 AM B10-5 Parameter Analysis of Reactive Sputtering Process with Surface Kinetics and Plasma Chemistry
C. Li (Nanyang Technological University, Singapore)
Surface kinetics and plasma chemistry play very important roles in the process of reactive sputtering. Many parameters such as the density and flux of electrons and ions, target sputtering rate, substrate deposition rate etc., can be estimated more accurately if the surface kinetics and plasma chemistry are included in the analysis. It is commonly known that the introduction of reactive gas in the reactive sputtering would create a transition from metal to compounds (oxides, nitrides and carbides, etc.) on both target and substrate surfaces. When the supply of reactive gas is beyond a critical amount, the excessive gas would result a sudden increase of its partial pressure. Furthermore, since the ion-induced secondary electron emission of compounds is higher than that of metal, the formation also triggers a sudden change of cathode voltage followed by the Ohm's law. All these phenomena actually originate from the interaction among neutrals, ion and electrons in the plasma region either near surfaces or away. In addition, all these phenomena too lead the well-known hysteresis loop in cathode voltage, sputtering rate and fraction of compound formation under different flow rates of reactive gas. Therefore, the stability is a very important issue in the process control. In this study, a simple mathematical model based on Berg's and Pekker's original proposal is used to carry out a parameters analysis for steady state solution of the hysteresis loop. In order to facilitate the analysis, several non-dimensional parameters are identified and the steady state solutions are obtained numerically. These non-dimensional parameters are also expected to be useful for process control in practices.
10:10 AM B10-6 Single Particle Impact Modeling in Multilayered PVD Coatings for Erosion Protection
M. Bielawski, W. Beres, P.C. Patnaik (National Research Council Canada)
One of the most pressing needs faced by the aerospace industry is the development of advanced coatings for erosion protection of gas turbine engine components. This is particularly important for military aircraft operating in desert conditions. Therefore, new coatings with properties exceeding those of existing materials and meeting higher environmental standards need to be develop. This requires advances in coating technology as well as in the material systems. One of the coating technologies considered for erosion protection application is Physical Vapor Deposition (PVD), particularly Unbalanced Magnetron Sputtering (UMS). Flexibility of the UMS technology allows for deposition of graded multilayered coating systems, including micro- and nano-structured wear resistant and erosion resistant coatings. In the paper, multilayered coatings made out of refractory metals and their compounds, with a composite structure designed to provide maximum erosion protection to the substrate were proposed. Nitrides or carbides of these metals were investigated since they have already been used successfully in monolithic coatings. The coating design efforts were guided by modeling the material response to impact load in simulated erosion condition using two- and three-dimensional finite element models and the ABAQUS/Explicit commercial software. Coating internal structures, such as number of layers, individual layer thickness and material properties, were analyzed to maximize attenuation of stress waves created by a single particle impact. The effect of additional elasticity on the coating system response was assessed. This paper reports on the preliminary modeling results, in terms of material properties and the coating internal structure.
10:30 AM B10-7 Composite Coatings for Mg Alloys Based on Oxide Ceramic Layers Produced using Plasma Electrolysis
A.L. Yerokhin (University of Sheffield, U.K.); P. Shashkov, A. Shatrov, V. Samsonov (Keronite Ltd., United Kingdom); T. Pilkington, A. Leyland, A. Matthews (University of Sheffield, United Kingdom)
Surface treatment is essential for magnesium alloys to improve poor tribological and anticorrosion performances. Recent developments in plasma electrolytic oxidation technology (PEO) offer new oxide ceramic layers with properties superior to that of conventional anodic films on Mg. However, the possibilities of using these layers as a matrix to develop new composite coatings have not been yet explored. In this work, a series of composite coatings is produced based on oxide ceramic layers formed by PEO on Mg alloys. Finishing methods employed to produce the composite coatings include (i) sol-gel, (ii) organic paint, (iii) PTFE spray; (iv) electroless Ni and (v) MO CVD topcoats. The coatings characteristics are studied using optical microscopy, SEM and surface profilometry; mechanical and tribological performances are evaluated by microhardness, scratch adhesion and linear reciprocation ball-on-plate tests; anticorrosion properties are revealed by potentiodynamic corrosion tests performed in NaCl solution. As a result of the study, the potential of new composite coatings with an oxide ceramic matrix is clearly demonstrated.
10:50 AM B10-8 Optical Characteristics of Oxide Coatings on Aluminium Alloys Produced by Pulsed Bipolar Plasma Electrolysis
T. Pilkington, A.L. Yerokhin (University of Sheffield, United Kingdom); P. Shashkov, V. Samsonov, A. Shatrov (Keronite Ltd., United Kingdom); A. Leyland, A. Matthews (University of Sheffield, United Kingdom)
Optical properties of oxide ceramic coatings , such as luminance (L*) and chroma (a*, b*), are related to surface chemical composition and structure. These characteristics can be effectively controlled using recently developed Pulsed Bipolar Plasma Electrolytic Oxidation. Correlation between the process parameters, structure, composition and optical properties was studied for the coatings produced on aluminium alloys. Techniques used for composition and structure analysis included XRD, SEM and optical microscopy. The colour and reflectance of the coatings were investigated using a commercially available Colourspectrophotometer. It was found that optical properties can be controlled to provide a surface colour from near white L*63 a*1.9 b*8.3 to black L*24 a*0.3 b*0.3, expressed in the CIELAB:1976 colour space. In addition, wear, scratch and corossion tests were used to compare coating performance with standard reference coatings.
11:10 AM Invited B10-9 Novel Hard and Wear Resistant Coatings on Aluminium Alloys Produced by Plasma Electrolytic Oxidation
P. Shashkov (Keronite Limited, United Kingdom)

Plasma electrolytic oxidation of Al alloys enables to produce hard and wear resistant ceramic layers of up to 150 micron thick with excellent adhesion to the substrate. Being a bath process it can treat parts of practically any shape and of a size upto few meters square provided appropriate source of electrical energy is developed. Industrial application of the process required creating of a Process Unit with control over four plasma electrolysis parameters to achieve a high deposition rate in the range of 3-10 microns per minute in combination with moderate specific energy consumption. The Unit applied specially modulated bipolar electrical pulses of kHz frequency range to the electrolytic bath which was supplied with aero-hydro dynamic agitation system.

The oxide ceramic layers were characterized by means of optical microscopy, SEM, EDX, XRD and surface profilometry. Microhardness, scratch and ball-on-disk tests were performed to evaluate mechanical performances. The effects of positive and negative current pulses duration and energy onto the kinetics of the layer growth, structural, morphological and mechanical characteristics are investigated.

11:50 AM B10-11 Oxide/lubricant Composite Coatings Deposited by using Electrolytic Plasma Process
L. Wang, X. Nie (University of Windsor, Canada); Y. Xiao (Chinese Academy of Science, PR China)
Weight-saving materials such as aluminum (Al), magnesium (Mg), titanium (Ti) and other alloys are becoming increasingly important, especially in the automotive and aerospace industries. However, these materials tend to have poor wear resistance. Various Coatings have been used on aluminum alloy to reduce friction and improve wear and scuff resistance. These coatings included composite polymer coatings (CPCs), nickel/ceramic composite coatings (NCC), DLC coating and hard anodizing etc. The purpose of this research is to deposit coating on aluminum alloy via an emerging electrolytic plasma processing (EPP) with selected suspended particles in solution. The particles such as Teflon, molybdenum disulfide (MoS2), boron nitride (BN) or graphite are selected for improvement of the wear and scuffing resistance as well as lubrication properties of coatings. The morphology, microstructure, and composition of EPP-deposited coatings were studied as a function of processing parameters and characterized by XRD, SEM and EDAX. A tribometer was used for investigation of tribological properties. Effects of the electrical and electrolytic parameters on tribological properties were discussed.
Time Period ThM Sessions | Abstract Timeline | Topic B Sessions | Time Periods | Topics | ICMCTF2004 Schedule