Innovations in Thin-film Manufacturing Processes

Wednesday, April 12, 2000 8:30 AM in Room Town & Country

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8:30 AM G1-1 Combined Reactive Deposition of TiAlN or CrN and Non-reactive MoS @sub2@
E. Pflüger (Centre Suisse d@super ‘@ Electronique et de Microtechnique SA, CSEM, Switzerland)
In the past few years, a sharp increase in interest for dry lubrication systems can be observed. Primary forces are exercised by ecological concerns. Also important are economics, namely the increasing cost of toxic waste treatment and having means on site to protect the workforce from the unhealthy influences of these used lubricants. @paragrapph@ MoS@sub 2@ is one of the potential candidates to fulfil these requirements. Considerable improvements have already been obtained to make MoS@sub 2@ coatings, well- known for space applications, applicable to terrestrial systems. Multilayering and alloying with different metals are upcoming and partially already industrially-used techniques. @paragraph@ The basis for these improved coatings is still MoS@sub 2@ , so whatever variation will be chosen, the final macroscopic parameters of the film are determined by the MoS@sub 2@ lattice. Hardness can be considerably increase, but seems to be limited to values about 1000 HV. @paragraph@ This paper reports on a new way including the lubricating properties of MoS@sub 2@ into a by itself already very hard coating. CrN and TiAlN as well-known hard coatings are foreseen as basic matrix. MoS@sub 2@ is taken as solid lubricant, incorporated as nanometer-sized clusters in this hard, wear resistant coating. @paragraph@ These coatings were deposited on different steel substrates and were characterized for mechanical and tribological properties such as adhesion, hardness, Young @super ,@s modulus and friction and wear by using a variety of techniques including scratch tester, depthsensing indentation, pin-on-disk tribometer and micro-abrasion tester, respectively. The structure and composition of the films have been studied by optical microscopy, TEM, SEM, AFM, RBS, XRD, SIMS and EDX
9:10 AM G1-3 Reactive Deposition of Nitrides and Oxides Using a Twin-Cathode Inverted Cylindrical Magnetron
V.W. Lindberg, A.R. Woodard (Rochester Institute of Technology); D.A. Glocker (Isoflux, Inc.)
Reactive deposition of nitrides and oxides of aluminum and other metals were done using a twin-cathode inverted cylindrical magnetron run with mid-frequency power. This geometry is particularly suited for coating three-dimensional objects of complex shape. However, high rate reactive sputtering in such an enclosed cathode has not been reported and presents unknown processing conditions. Dielectric coatings onto glass and polymer substrates have been successfully completed. Relatively high pumping speeds allow the investigation of process stability using gas flow control alone. The hysteresis behavior for the various systems studied will be presented.@paragraph@ Films were deposited under conditions of different pressure, power and reactive gas flow. In order to characterize the films, the reflectance, transmittance and absorbance of coatings deposited on glass slides were measured. Optical properties and deposition rates will be presented for the various conditions studied. In measuring these properties, particular attention was paid to the transition between metallic and poisoned modes of deposition. Adhesion and durability were also assessed.
9:30 AM G1-4 Closing the Coating Thickness Gap: LPPS Thin Film Technology
M. Loch (Sulzer Metco AG, Switzerland); G. Barbezat, P.J. Meyer (Sulzer Metco AG, Switzerland)
Using conventional thin film technologies it is either difficult or expensive to increase the coating thickness above 5µm. On the other hand it is hardly possible to receive coatings with a thickness below 50µm using thermal spray technologies especially if bigger areas have to be coated. Due to this, application which require coatings of a thickness between 5 and 50µm are suffering from the compromises typically taken. Thermally sprayed coatings using the LPPS Thin Film technology can close the gap between thermal spraying and thin film technologies. The process is based on a low pressure plasma spray process which is modified to achieve a large plasma plume. This plasma realizes a spray spot of about 400mm diameter (15 inches) covering a rather large surface area to be coated. Using this thermally sprayed thin film technology it is possible to coat several square meters of a surface within some few minutes with a thermally sprayable material like ceramic, metal or composite. @paragraph@ This paper will present some aspects of the actual development work pointing out coating characteristics and analysis results of ceramic and metallic coatings. It further will provide an outlook on possible application, especially as it will be an additional coating technology rather than a competitive coating technology for conventional thin film and thermal spray techniques.
9:50 AM G1-5 Enhancement of Machine Tool Spindle Performance Through Hybrid Bearings with Low temperature PVD coated rings
K.-D. Bouzakis, N. Vidakis, S. Mitsi, A. Lontos (Laboratory for Machine Tools and Manufacturing Engineering, Mechanical Engineering Dept., Aristoteles University of Thessaloniki, 54006, Greece)
Hybrid angular contact ball bearings with steel rings and silicon nitride rolling elements is a recent attainment that improves the rotating capacity, especially of high speed and precision machine tool spindles. Nowadays, bearing manufacturers offer special catalogues with commercial series, to enable an effective selection of the convenient hybrid bearings. Even though hybrid bearings are known as anti-friction bearings, they still hold a certain amount of friction in operation, related to the limited performance of their steel rings. Therefore, thin hard PVD coatings are used, which improve considerably the entire tribological accomplishment of hybrid bearings. Nevertheless, the coating lifetime may be reduced by coating fatigue phenomena, thus restricting the service life of the whole bearing. The present paper describes the application of critical coating fatigue stresses in fatigue calculations of hybrid bearing steel races. The fatigue limits of low temperature physically vapour deposited (PVD) coatings were determined by the application of the impact test and its evaluation software. A computer program that performs the quasi-static simulation of the bearing operation yields the necessary kinematics and dynamic parameters for the FEM simulation of the stress field occurring in coating rings. This procedure, being carried out for the recommended by catalogues load and rotational speed limits indicates whether a certain coating may be reliably used in the examined bearing or not. Such important data can be implemented into hybrid bearing catalogues as further technological recommendations related to the coating operation, for promising compounds. In this paper, the operating expectations of three PVD coatings, optimized for such applications, are analytically examined for two commercial angular contact hybrid bearings.
10:30 AM G1-7 CrN/NbN Superlattice Coatings Grown by the Cathodic Arc Evaporation Technique
R. Villa, L. Parenty (LAFER S.p.a., Italy); P. Juliet (CEREM, France); S.B. Lyon (UMIST, United Kingdom); P.Eh. Hovsepian, D.B. Lewis, W.-D. Münz (Sheffield Hallam University, United Kingdom)
CrN/NbN superlattice coatings have been deposited by cathodic steered arc evaporation in an industrially sized PVD coater. Prior to coating the substrates were subjected to a high negative voltage of 1.2 kV steered arc chromium metal ion etching. A 0.3@micron@ thick CrN base layer was then deposited by arc evaporation from two Cr targets to further enhance the adhesion of the coating. The CrN/NbN superlattice coating was deposited by operating two Cr and one Nb targets in steered arc mode in common nitrogen atmosphere. @paragraph@Arc deposited CrN/NbN coatings exhibited single phase f.c.c. structure and strong {220} preferred orientation. A well-defined superlattice structure with pronounced healing of the growth defects originating from the arc-generated droplets was observed by the X-TEM technique. Coatings with superlattice period in the range between 3nm and 6.7nm were produced by controlling the rotation speed of the samples during the deposition process. Maximum hardness values of HK@sub 25@@=@36 GPa were obtained for coatings with superlattice period of 3.7nm. Coatings produced in two and three fold rotation of the samples showed low friction coefficient in the range of 0.3, however the wear coefficient was relatively high of 8.19.10 @super 13@ m@super 2@ N@super 1@. The corrosion resistance of the arc deposited CrN/NbN superlattice coating was superior to that of monolithically arc grown CrN and NbN and comparable to that of 25@micron@ electroplated hard chrome.
10:50 AM G1-8 Microstructure and Properties of PIRAC Nitrided NiTi Surgical Alloy
I. Gotman, D. Starosvetsky, E.Y. Gutmanas (Technion, Israel)
There is increasing interest in applying coating technology to the improvement of wear and corrosion properties of shape memory NiTi alloys used for implants in the human body. In the present work, NiTi alloy was coated using a simple and original PIRAC nitriding method suitable for surface modification of large and complex shape implants. NiTi samples were annealed at 850-1100@super o@C in sealed stainless steel containers that allow selective diffusion of nitrogen atoms from the atmosphere. PIRAC nitrided surfaces were found to have a layered structure with a hard TiN outer layer followed by Ti@sub 2@Ni. The relationship between the microstructure, nitrogen concentration and microhardness was determined employing XRD, SEM/EPMA and High Resolution SEM. The kinetics of reactive coating formation was studied by measuring the layer thickness as a function of annealing time and temperature. Importantly for biomedical applications, corrosion resistance of PIRAC nitrided NiTi samples in Ringer's solution was markedly better than that of untreated NiTi, with no pitting corrosion observed up to 1.1 V, very low anodic currents in the passive region and an exceedingly low metal ion release rate. This, together with the excellent adhesion and high wear resistance of the TiN coatings, makes PIRAC nitriding an attractive surface treatment for NiTi alloy surgical implants.