ICMCTF2004 Session TS2: Self-Organization and Surface Response Effects in Thin Film Technology and Under Operation

Friday, April 23, 2004 8:30 AM in Room San Diego

Friday Morning

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8:30 AM TS2-1 Surface Engineering Issues in Nanoscience and Nanotechnology
S. Datta, Z. Klusek, H.L. Du, J.S. Burnell-Gray (University of Northumbria, United Kingdom)
Surface engineering processes are important considerations in nano-science and nano-technology. Nano-science and nano-technology allow investigation of surface engineering phenomena at a fundamental level in terms of work function and local density of states, nanoscale morphology, defect structures and chemical environments. On the other hand some surface engineering processes also offer ways to create molecular features which are essential for the advancement of nano-science and nano-technology. In this paper, we shall discuss these aspects at a most fundamental level from the information generated using scanning tunnelling microscopy (STM), scanning tunnelling spectroscopy (STS), current imaging tunnelling spectroscopy (CITS) and high resolution transmission electron microscopy (HRTEM). We shall present results from our studies on in situ functionalisation of tribologically generated surface with high wear resistance, phase transformation and degradation processes in CVD deposited DLC coatings, cluster formation during oxidation of TiAl and molecular pit formation with functionalities in treated graphites. We shall discuss the implications and significance of these findings.
8:50 AM TS2-2 TiAlN Based Nanoscale Multilayer Pvd Coatings Designed to Adapt their Tribological Properties at Elevated Temperatures*
P.Eh. Hovsepian, D.B. Lewis, Q. Luo (Sheffield Hallam University, United Kingdom); P.H. Mayrhofer, C. Mitterer (University of Leoben, Austria); W.-D. Muenz (Techno-Coat Oberflachentechnik)
TiAlN have proved to be increasingly useful in high temperature tribological applications due to their excellent oxidation and abrasive wear resistance. The addition of properly selected elements, coupled in nanoscale multilayer structures however, can further enhance their properties and bring new high performance triggered by diffusion processes at elevated temperatures in the bulk of the coating, or by phase transformations in thin surface layers during friction conditions. The incorporation of Y in the nanoscale pseudo-superlattice TiAlCrN/TiAlYN with typical period of 1.8 nm not only improves the oxidation resistance but also reduces the coefficient of friction of the coating from 0.9 to 0.65 at temperatures in the range of 850-950°C. The adaptation of the tribological properties occurs as a result of the preferential migration of the Y to the column boundaries, which effectively blocks the diffusion paths and promotes coating densification. This unique segregation behaviour is observed only if the Y is incorporated in a layered manner and the concentration is tightly controlled in the range of 1-2%. TiAlN/VN superlattices can achieve another self-adaptation process. During friction the coatings adapt themselves to the combined thermal and mechanical wear by the formation of highly lubricious vanadium-oxides. The oxide formation occurs due to high, (exceeding 650°C), flash temperatures at the asperity contacts, whilst the integrity of the bulk of the coating is retained, leading to exceptionally low, for superhard coatings, with friction and wear coefficients of 0.45 and 2.10-17 m3/ Nm.The coatings have been deposited by the Arc Bond Sputtering method. The excellent high temperature behaviour of the TiAlCrN/TiAlYN has found applications in dry high speed milling of hardened, (HRC =62) steels, whereas the TiAlN/VN superlattice coating has proven to be very efficient in cutting sticky alloys, such as Inconel 718 (HRC= 43).
9:30 AM TS2-4 Impact of TiAln PVD Coating’s Microstructure on the Formation of Protective Tribo-films during High-speed Cutting
G.S. Fox-Rabinovich, S.C. Veldhuis (McMaster University, Canada); A.I. Kovalev (Metallophysical Institute, Russia); N.A. Bushe, I.S. Gershman (Scientific Research Institute of Rail Transport, Russia); A.I. Dodonov (VIT Company, Russia); L.S. Shuster (McMaster University, Russia)
The use of Filtered Arc Deposition (FAD) technique has been shown to result in significant improvements in the TiAlN PVD coating’s microstructure and its physical properties. The investigation of dislocation, and electronic structures of the coatings was performed using TEM and EELS methods. The wear performance of the coatings was studied under conditions of high-speed machining. The friction parameter values vs. temperature of the regular as well as advanced Filtered Arc PVD TiAlN coatings were measured. The impact of the coating’s microstructure on the formation of tribo-films during friction in cutting process with TiAlN coated tools is considered based on approaches of non-equilibrium thermodynamics and self-organizing phenomena. It was shown that the increased density of the defects in FAD TiAlN coating leads to the critical acceleration of mass transfer to the surface during friction and thus enhance the formation of protective alumina films.
9:50 AM TS2-5 Elastic and Plastic Work of Indentation as a Characteristic of the Ability of Nitride PVD Coatings to Dissipate and Accumulate Energy during Friction
G.S. Fox-Rabinovich (McMaster University, Canada); V.N. Scvortsvo (Scientific and Research Institute for Machinery, Russia); S.C. Veldhuis (McMaster University, Canada); L.S. Shuster (Ufa Aviation Institute, Russia)
A study of the chemical and phase composition as well as structural characteristics and residual stress of the TiN-based PVD coatings vs. nitrogen pressure using AES, XRD methods was performed. The friction and wear characteristics of the coatings under different wear conditions were determined. The relation between the TiN PVD coating’s wear resistance and the ability of the coatings to dissipate the energy of plastic deformation as well as to accumulate the energy of elastic deformation obtained by nano-indentation method was outlined. The microhardness dissipation parameter (MDP) was developed as a ratio of energy dissipated during plastic deformation to the total energy of elastic-plastic deformation during nanoindentation to indicate a coating’s durability. An optimal range of the MDP for TiN as well as TiAlN PVD coating was suggested for the different wear modes of the cutting/stamping tools working under high external stress conditions. The connection between MDP and H/E ratio was also considered.
10:10 AM TS2-6 Self-arrangement in Hard Coatings
P.H. Mayrhofer (University of Leoben, Austria)
Nanostructures have attracted increasing interest for hard coatings. The high number of interfaces is often responsible for their superior properties, but these also stimulate microstructural processes. Whereas for single-phase coatings a remarkable reduction in hardness occurs around 500°C, nanocomposite coatings maybe stable up to 1000°C. Deposition of multi-component coatings often results in supersaturated metastable phases. A model system for this is Ti1-xAlxN with NaCl-structure. Annealing causes the metastable phase to decompose into its stable constituents fcc-TiN and hcp-AlN. Initially Ti1-xAlxN coatings undergo spinodal decomposition into coherent fcc-AlN and fcc-TiN nanometer-size domains, generating an increase in hardness at elevated temperatures (age hardening), due to coherency stresses. Further decomposition causes coarsening of the domains and eventual precipitating of fcc-TiN and hcp-AlN phases, resulting in a hardness decrease (overaging). Phase separation may also appear by nucleation and growth of stable phases like in TiB0.34N0.94. Here, annealing of a supersaturated fcc-TiB0.34N0.94 causes the formation of hcp TiB2 precipitates, where hardness increases due to modulus hardening. Another mechanism of structural self-arranging appears in TiB1N0.75 where, as-deposited, the supersaturated phases are in the nanometer range thus, spinodal decomposition within the crystalline phases is unlikely. Nanocomposite TiB1N0.75 consisting of boron-rich and nitrogen-rich nanometer-size phases reach their stable configuration fcc-TiN and hcp-TiB2 by diffusion across their boundaries. This causes also a hardness increase by the formation of a better-defined boundary structure. The results presented show that next generations coatings with increased ability for self-adaptation at elevated temperatures can effectively be prepared by plasma assisted vapor deposition.
10:50 AM TS2-8 Germanium Quantum Dots Growth by Ion-assisted Ion Beam Deposition
H.C. Chung, C.P. Liu (National Chung Kung University, Taiwan, R.O.C.)
Germanium quantum dots have been deposited onto silicon (001) substrates by single and dual ion beam deposition. The structural properties of the as-deposited films have been characterized by atomic force microscopy and transmission electron microscopy. Germanium dot size, shape, size distribution and density are examined as function of ion energy flux and temperature. In particular, the evolution of island shape and assembly are studied with the incident angle of the assisted gun. The results show that, with increasing ion energy in the energy rang of 0.8-1.5 kV, the germanium island size distribution becomes more uniform, the mean island size decreases while the island density increases. Thus, the island size as small as 10 nm can be achieved. Low-energy ion bombardment during deposition exerts a strong influence on the properties of the dots, particularly their size, orientation, and density. The increased island density is not a result of an increased island nucleation rate associated with defects produced in the Si substrate during ion beam-assisted deposition. In addition, for a fixed ion energy, an increased ion-to-atom flux ratio results in similar changes in microstructure distribution as is observed with increasing ion energy.
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