ICMCTF1999 Session D4/E5: Mechanical Properties and Applications of Diamond and Related Materials Coatings

Wednesday, April 14, 1999 8:30 AM in Room Forum/Senate/Committee

Wednesday Morning

Time Period WeM Sessions | Abstract Timeline | Topic D Sessions | Time Periods | Topics | ICMCTF1999 Schedule

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8:30 AM D4/E5-1 Scaling Relationships for the Abrasion of Steel by Diamondlike Carbon Coatings
S.J. Harris, A.M. Weiner (General Motors)
In previous work we found that the rate of abrasion of steel by metal-containing diamondlike carbon Me-DLC coatings is not constant but decreases significantly during the course of our test. In this work we provide quantitative scaling relationships which show how the time dependence of the abrasion rate of a steel ball by a Me-DLC-coated disk varies with important parameters of dry sliding wear such as sliding velocity, distance traveled, number of cycles, and wear track radius. We also demonstrate how to predict wear volume when the wear track radius is changed in the middle of an experiment. We show that changes in the Me-DLC coatings, not in the (steel ball) counterparts, are responsible for the reduction in the measured abrasion rates. We find that the volume of steel abraded does not depend on the average nominal contact stress between the coated coupon and the steel ball or on the state of wear of the ball.
9:10 AM D4/E5-3 Tribological Performance of Diamond-Coated Ti-6Al-4V Alloy with Respect to Diamond Characteristics
M.I. De Barros, J. Fontaine, L. Vandenbulcke (CNRS-LCSR, France); G. Farges (DGA, France); M. Vayer, P. Andreazza, R. Erre (University of Orleans - CNRS, France)

Various deposition conditions of diamond on Ti-6Al-4V alloys at 600°C in a microwave plasma were used to obtain different film characteristics. Both the nucleation and growth steps were varied to change the diamond films structure, their surface roughness and their composition, that is the sp3/(sp3+sp2) ratio. Coatings with overlayer of different composition were also deposited. Moreover some films were polished after diamond deposition to obtain a final roughness of about 8 nm (r.m.s.).

The diamond film characteristics were studied by visible and UV Raman spectroscopy, X-ray diffraction and AFM. Surface roughness of columnar polycrystalline and polynucleated nanocrystalline diamond films were determined in the 20-100 nm range. The sp3/(sp3+sp2) ratio was also varied from nearly one to about 50%.

These films were deposited on Ti-6Al-4V disks and pins. Sliding experiments were conducted in ambient air on a rotating pin-on-disk tribometer with uncoated and coated Ti-6Al-4V pins. The friction coefficient of uncoated pins on polycrystalline diamond films is in the 0.05-0.1 range after a running in period which is as short as the surface roughness is low. The nanocrystalline diamond films provide especially low friction coefficient and wear rate in comparison to polycrystalline films. The whole results including those obtained with the polished diamond films show the influence of the surface roughness. The influence of the sp3/(sp3+sp2) ratio however cannot be neglected. No coating failure or crack, and no stress relaxation are observed on the disk track even at high load. Sliding tests between two diamond-coated counterfaces evidence a self-polishing mechanism that leads to ultra smooth wear tracks and a low final wear rate. No more damage is produced by titanium arising in the contact when the diamond pin tip is partly worn during a long test.

9:30 AM D4/E5-4 Thermal Annealing Behaviour of Alloyed DLC Films on Steel: Determination and Modelling of Mechanical Properties
J. Michler, E. Blank (Swiss Federal Institute of Technology (EPFL), Switzerland)

Diamond-like carbon (DLC) films exhibit poor microstructural stability and properties at elevated temperatures. In this study, the effect of annealing on the stability of DLC films alloyed with silicon and deposited on steel is investigated. A comprehensive study of the mechanical properties, including adhesion and fracture strength, is carried out by a novel method combining normal indentations using micro- and macroindentors with finite element calculations of the indentation. The mechanical properties of the layers are correlated to structural changes in the film and to interface reactions.

While it has become a common practice to determine hardness and the Young's modulus of thin films by nanoindentation and to calculate residual stresses from the bending of the film/substrate system, evaluation of the interface toughness, which is a measure of adhesion, and of the film rupture strength is less straightforward. Here, Hertzian-type ring cracks are generated in the film by nanoindentation of the film/substrate system with spherical diamond tips. From the critical load for crack generation the film rupture strength is deduced using FEM. Similarly, Rockwell C hardness tests in combination with calculations are performed to measure the interface toughness.

Applying these methods to DLC films on steel, it has been found that the Young's modulus decreases with increasing silicon content and the residual stress drops below 1GPa. The rupture strength is close to its theoretical limit of E/10. Annealing up to 500°C reduces the adhesion energy significantly. The variation of mechanical properties can be attributed to structural changes in the film as investigated by Raman spectroscopy, X-ray photoelectron spectroscopy.

9:50 AM D4/E5-5 Well Adherent and Morphologically Controlled Diamond Coatings on Three Dimensional Engineering Components: A Physicists Dream or an Engineers Reality?
M. Rueffer (Universitaet Erlangen - Nuernberg, Germany); O. Lemmer (CemeCon GmbH, Germany); S.M. Rosiwal, R.F. Singer, E. Zeiler (Universitaet Erlangen - Nuernberg, Germany)
It is well known that diamond coated surfaces may show superior performance in tribological applications. This is due to the unique properties of diamond, for example its high hardness, low coefficient of friction and high thermal conductivity. The tribological properties are strongly related to the diamond structure and the surface morphology. The deposition of flat diamond layers with controlled α-factor is well established for electronic or optical applications. Concerning the three-dimensional coating of complex shaped tools or other engineering components in a production plant no systematic data exist yet dealing with the control of the α-factor during deposition. In this paper we present results on morphologically controlled three dimensional diamond coating of engineering components with a comercial hot-filament reactor (CC800DIA, CemeCon, Aachen). The relevant coating parameters are surface pretreatment, coating temperature (filament and substrate temperature), gas composition, gas pressure, gas flow and deposition time. The most important issues are the constancy and the reproducibility of the depostions parameters in a large reaction chamber. The diamond coated substrates were rods of titanium and cemented carbide. The simple shape allows to determine the influence of the subtrate geometry . The aims of these investigations are for example smooth diamond layers (<100> direction with (100)-facettes or nanocrystalline diamond) on the root section of titanium blades to prevent fretting fatique or homogeneous rough diamond coatings (<100> direction with (110)-facettes) on titanium hip joint shafts for better ingrowth of the human bone. The different tribological properties of the diamond coated parts in respect to the surface morphology will be discussed.
10:30 AM D4/E5-7 Optimization of Deposition Parameters of Diamond-like Thin Films as Antireflection Coatings for Solar Cells on Their Mechanical Properties
N.V. Novikov, A.G. Gontar, O.G. Lysenko, S.I. Khandozhko, V. Grushko, S. Dub (V.Bakul Institute for Superhard Materials, UKRAINE)
The method of RF (13.56 MHz) discharge CVD from a methane-hydrogen mixture has been used to prepare diamond-like antireflection coatings for silicon solar cells as well as Si and Ge optical elements operating in IR spectral range By the variation of deposition parameters (the bias voltage and the gas mixture composition) the mechanical and protective properties of diamond-like films were optimized for preparing hard, slightly stressed, chemically stable coatings to protect surfaces functioning under conditions of corrosive environment. The procedure for measuring mechanical properties of films has been Developed which uses methods of nanoindentation, tunnel microscopy and acoustic emission. The relation between deposition parameters, microstructure and properties of coatings for solar cells has been studied.
10:50 AM D4/E5-8 Cutting Behavior of Diamond Coated Cutting Tools according to Various Kinds of Workpiece Materials
Y.-J. Baik, W.S. Lee, K.Y. Eun (Korea Institute of Science and Technology, Korea); K-W. Chae (Precision Diamond Inc., Korea)
Cutting performance of diamond coated insert tools is investigated. Cemented carbide substrates, based on WC-Co, are used, where Co and cubic carbide range from 7% to 15% and 0% to 20% respectively. The substrates are pretreated for the interface adhesion using either etching or heat-treatment. The adhesion is so excellent that no delamination occurs under the Rockwell indentation of 150Kg load in the case of 30 micron meter thick diamond film. However, the film coated on the etched substrate is delaminated from time to time, while that on the heat treated substrate maintains its adherence. No delamination is observed when cutting Al-18%Si workpieces. Various kinds of workpieces, such as Al-Si alloy, carbon-carbon composite, semi-sintered and sintered WC-Co alloy and semi-sintered ceramics are tested using these tools. The cutting performance appears to depend greatly on the kinds of workpiece materials. The comparison with the hard coated tools and polycrystalline diamond tools shows that the tool life enhancement is dependent on the degree of chemical interaction between workpiece and tool materials. Problems of diamond coated tools are also discussed.
11:10 AM D4/E5-9 Effect of Nitrogen Doping on the Mechanical Properties of Tetrahedral Amorphous Carbon Films Deposited with Filtered Cathodic Vacuum Arc
E. Liu, X. Shi, H.S. Tan, L.K. Cheah, Z. Sun (Nanyang Technological University, Singapore)
The mechanical properties of both undoped and nitrogen doped tetrahedral amorphous carbon (ta-C and ta-C:N) films, such as hardness and E-modulus, are investigated. The mechanical properties are related to the film structures. The ta-C and ta-C:N films are prepared in a filtered cathodic vacuum arc (FCVA) process. For the deposition of ta-C films, a pure graphite target is used as the cathode. For the ta-C:N films, an ion beam gun is used to provide the nitrogen ions needed for nitrogen doping in the films. A nanoindenter is used to measure the mechanical properties of these films. Since the thickness of films prepared for this study is less than 100 nm, a continuous stiffness technique is therefore used to determine the mechanical properties of these films. The continuous stiffness technique can continuously monitor the film stiffness during loading, the hardness and Young's Modulus are therefore derived from the stiffness values. For the lightly doped ta-C:N films, the mechanical properties are competitive with those of undoped ta-C materials. However, with the further increase of nitrogen content in the films, the mechanical properties reduce. The extent of decrease of the mechanical properties of ta-C:N films shows dependence on the content of nitrogen in the films. The reason may be due to the nitrogen doping efficiency. The excess nitrogen atoms contained in the films may create C/N compounds or more sp2 clusters. The C/N compounds may promote the transformation from the sp3 bonding structure to sp2 structure and further enlarge the size of sp2 clusters, which causes the reduction of mechanical properties of the heavily doped ta-C:N films.
11:30 AM D4/E5-10 Effect of Hydrogen on the Mechanical Properties of CNx Films and their Possible Fullerene-like Microstructure
V. Hajek, K. Rusnak, J. Vlcek (University of West Bohemia, Czech Republic); L. Martinu (Ecole Polytechnique, Canada); S.C. Gujrathi (Universite de Montreal, Canada)

Crystalline ß-C3N4 was predicted to exhibit extreme properties, such as hardness, comparable to that of diamond. Although the synthesis of this crystalline metastable phase has not been fully confirmed yet, the already prepared amorphous CNx films possess excellent mechanical properties, including high hardness, elastic recovery (up to 90 %), and interesting tribological characteristics. Films having such properties, and prepared at the temperatures above 200 °C, using magnetron sputtering, are predicted to possess fullerene-like microstructure.

In the present work we deposited amorphous CNx films on Si substrates by reactive DC magnetron sputtering of graphite target in nitrogen plasma at a substrate temperature of 600 °C. The films are substoichiometric in nitrogen, with its concentration ranging from 12 to 24 at. %. Elastic recoil detection (ERD) analysis revealed a concentration of hydrogen between 1 and 5 at. % in the bulk of the films. The nitrogen concentration increased while the hydrogen concentration decreased with the substrate bias voltage ranging from -300 to -700 V. Increased hydrogen content was accompanied by decreased quality of mechanical properties (hardness from 23 to 2 GPa, elastic recovery from 74 to 40 %, lower adhesion), by higher film electrical resistance (from 20 to 970 Ωcm), and by the formation of C-H and N-H bonds (confirmed by FTIR). We suggest that excessive amount (> 1 at. %) of hydrogen in the films inhibits crosslinking between graphite-like planes containing carbon and nitrogen, and it thus hampers formation of the fullerene-like microstructure.

Time Period WeM Sessions | Abstract Timeline | Topic D Sessions | Time Periods | Topics | ICMCTF1999 Schedule