ICMCTF2006 Session E4: Tribology of Diamond, Diamond-Like and Related Carbon Coatings/Thin Films

Thursday, May 4, 2006 1:30 PM in Room California

Thursday Afternoon

Start	Invited?	Item
1:30 PM		E4-1 Triode Plasma Nitriding and PVD Coating: a Successful Pre-Treatment Combination to Improve the Wear Resistance of DLC Coatings on Ti6Al4V Alloy J.C. Avelar-Batista, E. Spain, J. Housden (Tecvac Ltd., United Kingdom); G.G. Fuentes, R. Rodriguez (Centre of Advanced Surface Engineering-AIN, Spain) Diamond-like carbon (DLC) coatings have found great applicability in the automotive industry because of their low friction coefficient and high wear resistance. Nevertheless, their tribological performance can be greatly reduced on soft substrates such as titanium alloys. The hard, brittle DLC coating cannot usually follow elastic and plastic deformation of the substrate without failing. In order to overcome this property mismatch between hard coating and soft substrate, triode plasma nitriding was applied as a pre-treatment to improve the mechanical properties of theTi6Al4V alloy and further enhance the load support for the DLC coating. DLC and multilayered TiN/DLC, CrN/DLC CrAlN/DLC coatings were deposited onto "standard"and plasma nitrided Ti6Al4V substrates. Triode plasma nitriding increased the load-bearing capacity of the coating/substrate system, as higher critical adhesion loads were recorded for DLC coatings on plasma nitrided Ti6Al4V substrates. This treatment also reduced the wear rate of the DLC coating/substrate. Further load support and lower wear rates were achieved by using TiN, CrN and CrAlN as intermediate layers on plasma nitrided Ti6Al4V substrates.
1:50 PM		E4-3 Effect of Tribological Media on Tribological Properties of Multilayer DLC/Cr(N) Coatings L. Wang, X. Nie (University of Windsor, Canada); Y.-T. Cheng (General Motors); J. Jiang (Louisiana State University) In this research, DLC/Cr(N) multilayered coatings are deposited on M2 steel substrates by an unbalanced magnetron sputtering technique. By varying the substrate rotation speed, four multilayered coatings with different bilayer thickness are produced. The bilayer thickness, interface and multilayer structure are characterized by Transmission Electron Microscope (TEM). Nanoindentation is used to measure hardness and elastic modulus of coatings. The investigations are particularly focused on the effect of layer thickness and tribological media on tribological property of multilayer DLC/Cr(N) coatings against Al counterface. A pin-on-disc tribometer with a tribological medium container is used to investigate the wear behaviours of the four multilayered coatings under dry and wet (tribological media including: distilled water, coolant and engine oil) sliding. The investigation of wear tracks and wear mechanism are performed using Scanning Electron Microscope (SEM) with Energy Dispersive X-ray analysis (EDX). The research results show that coatings with different bilayer period perform different tribological behaviour. The proper tribological media applied in the wear tests can improve the wear properties of multilayer coatings. Key words: Multilayer coatings, PVD, tribological properties, nanoindentation.
2:10 PM		E4-4 Mechanical and Tribological Characterization of CN_x Films Deposited by DC Magnetron Sputtering L. Yate, L. Ipaz (Universidad del Valle, Colombia); T. Polcar (CTU in Prague, Czech Republic); E. Camps (Instituto Nacional de Investigaciones Nucleares, Mexico); G. Zambrano, P. Prieto (Universidad del Valle, Colombia) Carbon Nitride (CN_x) thin films were deposited onto silicon and steel substrates at 300 °C from a carbon target by d.c. magnetron sputtering system. The composition and structural properties of deposited films were investigated as a function of argon/nitrogen concentration and sputtering power, by means of Electron Diffraction X-ray Spectroscopy (EDX), and Fourier Transform Infrared Spectroscopy (FTIR). The EDX analysis showed that the nitrogen concentration in the CN_x deposited films varied between 24% and 28% at different nitrogen concentrations in argon/nitrogen gas mixture, and deposition power. FTIR analysis indicated the presence of 2229 and 2273 cm^-1 stretching peaks associated with CN triple bonds of nitriles and isocyanides, 1640 cm^-1 and 1545 cm^-1 associated with the C=C and C=N, and a peak at 1730 cm^-1, which is connected to the C=O carbonyls groups. The thickness of the CN_x deposited films varied between 0.5 and 1.0 µm at different sputtering powers. The hardness and Young's modulus were investigated by depth sensing indentation. Adhesion of the coatings was measured by the scratch-test method. The friction and wear tests of were done using a pin-on-disc tribometer in dry air and humid atmosphere; 100Cr6 and Si₃N₄ balls were the sliding partners. The wear tracks were investigated by scanning electron microscopy (SEM) and the main wear mechanisms were tentatively described.
2:30 PM	Invited	E4-5 Boundary Lubrication and Superlubricity by OH-Terminated DLC Surfaces J.M. Martin, M.I. De Barros-Bouchet (Ecole Centrale de Lyon, France); W.A. Goddard (California Institute of Technology); M. Kano (Nissan Motors Co Ltd., Japan) Superlubricity in presence of DLC-coated surfaces (friction coefficient below 0.01) has already been observed by several authors, but only with hydrogenated DLC (a-C:H) in ultrahigh vacuumfootnote1, in inert gases (nitrogen)footnote2 and in hydrogenfootnote3. Under boundary lubricated condition, surprisingly, such low friction level has not been observed experimentally in the literature. Recently, we have discovered a new specific combination of ta-C (hydrogen-free DLC) coating and ester lubricants providing such extremely low friction under mixed and boundary conditions⁴. The mechanisms of superlow friction was investigated by using both surface sensitive analytical techniques (EV-XPS and ToF-SIMS) and also by using molecular dynamics simulations. We experimentally observed that an ultrathin tribofilm is formed (thickness less than 2 nm) and is responsible for such low friction and wear. This situation is particularly well adapted to computer simulation with MD technique. The conjonction of the two approaches lead us to the conclusion that a OH-terminated carbon surface was formed under friction and provides a new situation of superlubricity under boundary lubrication. This finding is indeed very important for future applications in lubricated systems where low friction and wear are needed in friendly environment. ¹ J. Fontaine et al, Surface and Coatings technology, 146-147, (2001) 286. ² A. Erdemir, Tribology International 37, (2004) 577 ³ C. Donnet et al ; Tribology Letters, 9 (2001) 137.⁴ M. Kano et al, Tribology Letters, Vol 18, No 2, (2005) 245.
3:10 PM		E4-7 Structure and Tribology of Diamond-Like Carbon from First Principles Theory and Simulation W.A. Goddard, Q. Zhang, A. van Duin, T. Cagin (California Institute of Technology); J.M. Martin, M.I. De Barros-Bouchet, T Le Mogne (Ecole Centrale de Lyon, France); M. Kano (Nissan Motors Co Ltd., Japan) We report the structure and tribological properties for hydrogen-free amorphous Diamond-Like-Carbon (denoted as ta-C) determined from first principles computer simulations using the ReaxFF reactive force field to create an atomistic model of ta-C. The 3D structure was determined by heating diamond until it melts and then quenching rapidly. These simulations lead to a density of 3.18 g/cc in good agreement with experiments from the JM Martin group in Lyon and the M Kano group at Nissan. This suggests that the simulations lead to a structure similar to that synthesized under appropriate CVD conditions. The simulations find that the bulk structure has 59% sp³ carbons joined together to form a percolating 3D arrangement to which sp² and sp¹ carbons attach in chains of length 1 to 3. This structure is consistent with SIMS experiments from Lyon. The simulations find a high percent of reactive C at the surface that reacts readily to form a very smooth carbon surface containing OH-terminated groups in agreement with the experiments from Lyon. The simulations find that systems lubricated with glycerol lead to from strong noncovalent interactions between the glycerol and the OH terminated surface that causes one monolayer of the glycerol to stick near the surface for long periods during sliding. Thus all sliding motions are confined within the lubricant film. This may be responsible for the superlubricity observed by Nissan for hydrogen-free amorphous Diamond-Like-Carbon.
3:30 PM		E4-8 Tribological Behavior of Nano-Undulated Surface of Diamond-Like Carbon Films in Various Humid Conditions J.W. Yi, S-.J. Park, K.-R. Lee (Korea Institute of Science and Technology, Korea); S.S Kim (Kyungpook National University, Korea) Tribological behavior of nano-undulated diamond-like carbon (DLC) films of the surface roughness ranging from 0.6 to 13.7 nm was investigated in air with various relative humidity (RH) levels. The nano-undulated DLC films were prepared by radio frequency plasma-assisted chemical vapor deposition (r.f.-PACVD) using nano-sized Ni dots on a Si (100) substrate. The friction coefficient between the DLC film and the steel ball was measured by a ball-on-disc type wear rig. The average friction coefficient has a trend that it increased with increase in the relative humidity. However, DLC film of rough surface showed that the frictional behavior was little affected by environment conditions. In all cases, while the frictional behavior of DLC film was not affected by roughness of surface, the wear rate of the steel ball increased with increase in the surface roughness. Auger and Raman spectroscopy analysis of the debris revealed that the tribochemical reaction with relative humidity was significantly suppressed as the surface roughness increased. Even if the rough surface increased the wear rate of the steel ball and thus the concentration of Fe in the debris, the oxidation of Fe or the graphitization of the carbon in the debris were not observed on the rough surface.
3:50 PM		E4-9 Friction Behaviour of Diamond-Like Carbon Films with Varying Mechanical Properties R.-A. Singh, E.-S. Yoon, H. Kong, S-.J. Park, K.-R. Lee (Korea Institute of Science and Technology, Korea) The friction behaviour of diamond-like carbon (DLC) films with varying mechanical properties was experimentally studied at nano/micro-scale. The films were coated on silicon wafers using radio frequency plasma-assisted chemical vapor deposition method. These films had varying mechanical properties such as hardness and Young's modulus. The thickness of the films varied from 100 nm to 1 µm. Friction at nano-scale was measured using atomic force microscope (AFM) and that at micro-scale using a ball-on-flat type micro-tribotester. The effect of contact area on friction of the test samples was also studied at these scales by using tips/balls of various radii. Silica (SiO₂) glass balls with radii of 0.32 to 2.5 µm attached on the top of AFM tip were applied for nano-scale contact and Soda Lime balls with radii of 0.25 to 1mm were used for micro-scale. Friction was measured with the applied normal load in the range of 0-160 nN at the nano-scale and 1500-4800 µN at the micro-scale. Results showed that the friction at nano-scale increased with the applied normal load and tip size for all the samples. It was also observed that the surface energy of the films influenced their friction behaviour. At micro-scale, films with thinner thickness showed increase in friction with the ball size. However, the thicker film (1 µm) showed a reverse trend. This distinct difference in the behavior of friction of films with varying thickness was attributed to the variation in their mechanical properties, contact area and the operating mechanisms. Further, unlike at the nano-scale, the friction of the test materials at micro-scale was affected by their wear. Evidences of operating mechanisms at micro-scale were obtained using a scanning electron microscope (SEM). It was observed that films with lower thickness exhibited adhesion, while the thicker film (1 µm) exhibited ploughing.
4:10 PM		E4-10 In Situ Tribology of Nanocrystalline Diamond Coatings R.R. Chromik (US Naval Research Laboratory); A.L. Winfrey, R.J. Nemanich (North Carolina State University); K.J. Wahl (US Naval Research Laboratory) Nanocrystalline diamond (NCD) coatings have been shown to exhibit a number of desirable properties for tribological applications including high hardness, low friction and good wear resistance. For this study, NCD coatings were prepared using a microwave plasma with hydrogen, argon, and methane. The ratio of H:Ar was varied in the growth plasma such that the H concentration ranged from 0 to 64% of the total gas flow. Coatings prepared over this range of deposition conditions exhibited different morphologies, roughness, crystalline orientation and graphite content. Friction and wear testing were performed using both rotating pin-on-disk and reciprocating ball-on-flat tribometers with hemispherical sapphire counterfaces. In situ studies using optical microscopy were conducted through the sapphire to examine the mechanisms controlling friction and wear. For all coatings grown with 0-36%H in the plasma, a steady-state friction coefficient of 0.05 was realized; a coating grown with 64%H in the grown plasma exhibited high friction (µ>0.2), significant counterbody wear, and early failure after only 50 sliding cycles. Coatings grown in plasmas containing less hydrogen exhibited variation in the run-in friction behavior that was correlated with differences in coating structure, chemistry, and roughness. In general, coatings with higher roughness, a tendency to (111) orientation and higher graphitic content realized shortest run-in and maintained low friction for >1500 cycles.
4:30 PM		E4-11 Solid-Film Lubricants Evaluated for Galling and Wear Protection of Ti-6Al-4V Under Fretting Conditions K. Miyoshi (NASA); J.H. Sanders (Air Force Research Laboratory); K.W. Street (NASA); R.L. Vander Wal (NCMR); R. Andrews (University of Kentucky) This study investigated whether solid-film lubricants could decrease the wear and galling of Ti-6Al-4V in cyclic relative motion. Fretting experiments in cyclic relative motion were conducted with 10-wt% TiC/Ti-6Al-4V hemispherical pins in contact with solid-film lubricants "multiwalled carbon nanotubes (MWNTs), diamondlike carbon (DLC), molybdenum disulphide, and graphitelike carbon (GLC)" coated on Ti-6Al-4V disks and in contact with bare alloy disks of Ti-6Al-4V, Ti-48Al-2Cr-2Nb, and nickel-based superalloy 718. The dispersed MWNT coating reduced pin and disk wear so much that they were almost not measurable. When an MWNT-coated Ti-6Al-4V substrate disk was brought into contact with a composite TiC/Ti-6Al-4V pin under fretting, protecting both the pin and disk from wear. The wear volume loss of a composite TiC/Ti-6Al-4V pin fretted against DLC/Cr-, molybdenum disulphide/Ti-, and GLC/Cr-coated on Ti-6Al-4V disks by magnetron sputtering was 1/274th, 1/251st, and 1/247th, respectively, of that fretted against bare Ti-6Al-4V. The wear volume loss of DLC/Cr-, molybdenum disulphide/Ti-, and GLC/Cr-coated Ti-6Al-4V disks was 1/88th, 1/64th, and 1/10th, respectively, of that of bare Ti-6Al-4V. When solid-film lubricants were applied to Ti-6Al-4V, alloy-to-alloy contact was avoided, and no galling occurred in the contacts during fretting. When bare alloy disks were brought into contact with TiC/T-6Al-4V, however, strong adhesion, galling, and severe fretting damage occurred in the contacts. This investigation indicates that solid-film lubricants may be suitable antigalling and antiwear films for aerospace applications under fretting conditions.
4:50 PM		E4-12 Sliding Wear of Non-Hydrogenated Diamond-Like Carbon Coatings Against Magnesium E. Konca (NSERC/GM of Canada/ University of Windsor Industrial Research Chair, Canada); Y.-T. Cheng (General Motors Research and Development Center); A.T. Alpas (NSERC/GM of Canada/ University of Windsor Industrial Research Chair, Canada) Due to its lower density, increasing the use of magnesium based parts brings significant weight reductions to motor vehicles, which in turn means improved fuel economy and less adverse impact on environment. Meanwhile, implementation of appropriate coatings on tool and die surfaces can substantially increase the productivity of the manufacturing processes (e.g. cutting and sheet forming) of Mg based parts as well as improving the surface quality of the finished products. Hence, as a potential tool coating for non-ferrous materials, the tribological behaviour of diamond-like carbon (DLC) coatings against Mg is of interest. In this study, dry sliding wear behaviour of magnetron sputtered non-hydrogenated DLC coatings deposited on M2 steel discs was investigated against rounded pins (4 mm dia.) of Mg (99.9 wt. %) using a vacuum pin-on-disc tribometer. Tests were performed in air (22 %RH) and in argon under a constant load of 5 N and a sliding speed of 0.12 m/s. In argon, the non-hydrogenated DLC coatings showed low wear rates and low coefficient of friction (COF = 0.05) after a running-in period. Carbonaceous material transfer from the non-hydrogenated DLC to the contact surface of Mg pin was observed in argon. Contrary to the previously reported studies on the tribology of non-hydrogenated DLC coatings against steel or ceramic counterfaces, changing the test atmosphere from argon to ambient air adversely affected the COF and wear rate of non-hydrogenated DLC against Mg. The average COF between non-hydrogenated DLC coating and Mg was 0.44 in air (22 %RH). Formation of oxidized Mg debris, in the forms of plate-like and rounded fine pieces, was observed in ambient air. This presentation will discuss the friction and wear mechanisms of non-hydrogenated DLC coatings against Mg in terms of i) generation of a carbonaceous transfer layer on the Mg counterface, and ii) chemical affinities of the DLC/Mg sliding pair against each other and towards the environment.