Papers

ICMCTF2003 Session E1-3: Friction and Wear of Coatings

Friday, May 2, 2003 8:30 AM in Room Royal Palm 1-3

Friday Morning

Start	Invited?	Item
8:30 AM		E1-3-1 Wear and Friction Characteristics of PVD-Coated Roller Bearings P.W. Gold, J. Loos (Institute for Machine Elements and Machine Design); M. Kuhn (Institute for Machine Elements and Machine Design, Germany) It was systematically examined on the basis of cylindrical roller thrust bearings to what extent PVD-coatings are able to take over the function of EP/AW-additives. The bearings were tested under heavy-duty conditions in order to distinguish the efficiency of different coating-substrate-systems very quickly. Two Me-C:H-coatings showed the best performance of the investigated coatings and fulfilled the required criterion for roller bearings in the boundary friction. Least wear took place, if only the bearing washers were coated. Material carryover from the carbonaceous coating to the steel surface was developed by the first Me-C:H-coating, WC/C, during the test. This phenomenon could not be observed for the second Me-C:H-coating, W-C:H. The un-coated counterpart, the bearing rollers, were protected in both cases by different protection mechanisms. The effect of different carbon-content concentrations was investigated on the W-C:H-coating. The lost of mass and the results of surface measurements revealed, that the amount of carbon in the coating is very important of the inner cohesion of the coating. Light microscopy and scanning electron microscope photos give the evidence, that for a too high concentration of carbon in the coating the coating fails in itself on the location of highest carbon concentration gradient. Several tests were performed to find out the number of WC/C-coated rollers running on un-coated washers in a cylindrical roller thrust bearing to achieve a sufficient bearing life-time. It could be seen, that the carbon coating is not only transferred to the un-coated washers, it was also found on the un-coated rollers. It came to a double carbon material carryover.
8:50 AM		E1-3-2 The Study on Wear Behaviors of Nitride Layers of Fe-Mn-Al-C Alloys J.H. Jaw, C.J. Wang (National Taiwan University of Science and Technology, Taiwan, ROC) The wear behaviors of high toughness austenitic Fe-30Mn-(2, 5, and 6wt%)Al-0.7C-(3Cr) alloys with/without nitriding in pure nitrogen were studied by a TE77 frictional test machine in a reciprocating sliding mode. Microstructures of alloys were also examined. The results showed that AlN was the major product and AlN pegs grew into the alloy substrate was the typical morphology of all alloys after nitriding at 1050°C for 25 hr. After nitriding, the surface hardness of alloy and the density of needle-like AlN in alloy substrate increased with the Al content. Besides, the addition of Cr enhanced the formation of AlN. Due to the increase of surface hardness and the pegging effect, the wear resistance performance of alloy was improved by the nitriding and pronouncedly by the Al content of alloy.
9:10 AM		E1-3-3 Machinability of Weld Hardfacing Deposits for Forging Tooling M. El Mansori, L. Fouilland, F. Pierron (ENSAM, France) Forging die and mould are subjected, in operation, to extreme mechanical and thermal loads to which conventional heat treatment cannot sufficiently react. Thus, surface coating such as weld surfacing becomes particularly important. Indeed, in hot forging dies, Nickel-base and Cobalt-base superalloys are typically used as weld-deposited hardfacings because of their outstanding strength and resistance to oxidation at high temperature (>550°C). However, their poor machinability remains a critical issue. The difficulty encountered when machining Nickel-base and Cobalt-base superalloys is primarily caused by the metallurgical characteristics responsible for their good strength and creep resistance This is traduced during machining by their noteworthy work-hardening and huge reactivity with the tool material leading to early wear of cutting tool. This paper presents the results obtained with different cutter/inserts combinations when machining these two hardfacing superalloys under various cutting conditions. The factors that can improve their machinability will be enumerated and discussed.
9:30 AM		E1-3-4 Tool Wear in Drilling Operations Under Magnetic Field M. El Mansori (ENSAM, France); D. Paulmier (Equipe ERMES, France) To prevent wear in various kinds of friction assemblies, magnetic-abrasive finish treatment is one of the recently used processes. Recently, we published some data on the magnetic field effects on HSS tools durability during machining [1,2]. Cutting tests consisted on turning experiments to establish some relation between the applied magnetic field intensity and the HSS tool durability. The tool durability was defined as the necessary time for the outage (catastrophic failure criteria) of the cutting tool during machining. We have observed high values of tool durability at higher level of magneto-mechanical excitation which is characterized by higher magnetic field intensities and cutting speeds. Nevertheless, more investigations are needed to determine the extent of influence of the different wear mechanisms on the cumulative tool wear. This paper completes previous studies concerning the mechanisms governing tool wear in metal cutting under an external applied magnetic field ¹. M. El Mansori, K. Lafdi and D. Paulmier, Enhanced wear resistance and tools durability using magnetization, In Metal Cutting and High Speed Machining, Kluwer Academic / Plenum Publishers, (2002) 301-310 ². M. El Mansori, F. Pierron and D. Paulmier, Reduction of Tool Wear in Metal Cutting Using External Electromotive Sources, Surface and coatings technology, (2002) in press.
9:50 AM		E1-3-5 Effect of Nitriding and Duplex Coating on the Performance of Twist Drills J.R.T. Branco (Fund Centro Tecnológico de Minas Gerais (CETEC ), Brazil); V.H. Baggio-Scheid (Centro Tecnico Aeroespcacial, Brazil); G.S. Vieira (Centro Tecnica da Aeronautica, Brazil); I.F. Silva (Rede Temática Em Engenharia de Materiais REDEMAT, Brazil) Drilling continues to be an important step for equipment manufacturing. In order to decrease machining cost, companies are looking for tools with higher wear resistance, lower cost and machined surfaces with high quality. Surface hardening by nitriding is being explored as a hard coating pre-treatment that, by giving the surface higher load bearing capacity, may enhance drilling tool life. In this paper drilling of AISI D3 with nitrited and duplex coated high speed drills was investigated. The nitriding was performed at 450 Celsius, under 15kHz pulsed plasma, 55 microseconds pulse width and at 300 Pa of nitrogen and hydrogen atmosphere, aiming zero thickness white layer. The nitriding time varied between 30 and 200 min. Hard TiN coating was deposited by triode e-beam ion plating at 3 levels of substrate temperature, between 250 and 450°C. The tools performance was measured by drilling motor current, drill flank wear rate and number of blind holes drilled. The results are discussed in terms of nitrited layer hardness and depth, micro- abrasion resistance and critical scratching loads.
10:30 AM		E1-3-7 Tribological Behaviors of Sputtered Carbon Films Under Light Loads J.-J. Rha, K.-S. Nam, K.-H. Lee (Korea Institute of Machinery and Materials, South Korea) For the purpose of applications in MEMS, sputtered carbon film was studied. In these application areas, passivation layers should have low friction, wear and adhesion simultaneously. Synthesized carbon films on Si wafer had surface roughness of lower than 3nm. Friction forces were measured with Rockwell C scale diamond indenter, Si₃N₄ ball and carbon coated on them respectively as a slider. Measured coefficients of friction ranged 0.02 to 0.5 according to applied loads and kinds of sliders. When diamond slider slid on carbon film under loads ranged 0.001 to 0.01N, the slope of a graph plotted friction coefficient versus applied loads in log scaled axes was -0.36, which was corresponded to elastic contact. Wear track could not be found. When applied load increased to 0.5N to accelerate wear with Si₃N₄ sliders, coefficients of friction were close to 0.1 and magnitudes of wear coeeficients were a few 10_-6.
10:50 AM		E1-3-8 Plasma Immersion Ion Implantation of PTFE T.L. Schiller (CSIRO, Australia); D. Sheeja (Nanyang Technological University, Singapore); D.R. McKenzie (University of Sydney, Australia); D.S.P. Lau (Nanyang Technological University, Singapore); D.G. McCulloch (Royal Melbourne Institute of Technology University, Australia); B.K. Tay (Nanyang Technological University, Singapore) Plasma immersion ion implantation (PIII) has been used with a filtered cathodic arc to implant Poly(tetrafluoroethylene) (PTFE) with copper and carbon ions. The carbon-implanted specimens were oriented with the surface parallel to the drifting velocity of the plasma to minimise the deposition of low energy species. The substrates for the copper implantation were placed perpendicular to the plasma beam. Electrodes in the form of a backing plate and a mask with holes were used to apply the pulsed bias from the PIII supply. The implanted PTFE has been examined for improvements in indentation hardness and tribological characteristics. A decrease in the coefficient of friction was observed, but surprisingly this was accompanied by an increase in wear. X-ray photoelectron spectroscopy (XPS) has shown that there is a structural change in the PTFE induced by both the copper and carbon implantation. Raman spectroscopy of the carbon implanted samples showed the presence of an amorphous carbon peak, which was reduced by cleaning the surface to remove carbon film, but a substantial amount remained. This shows that there is both implantation and deposition of the carbon occurring. The structural change in the PTFE is supported by FTIR results. A structural model for the modified polymer is proposed.
11:10 AM		E1-3-9 Dry Sliding Wear of TiNx-PVD Coatings on 7075-T6 Aluminum Alloy M.H. Staia, Y.Y. Santana, Z. Marcano, M.R. Cruz (Central University of Venezuela) The aim of this paper is to study the dry sliding wear behavior of a 7075-T6 aluminum alloy coated with three different under stoichiometric TiNx films. The coatings were deposited industrially (Teer Coatings Ltd.) by using the closed field unbalanced magnetron sputtering ion plating (CFUMSIP) deposition technique. Coatings characteristics such as morphology, thickness, compositional variation with thickness, residuals stress, composite microhardness are also presented. The wear tests were conducted in a ball-on-disc tribometer where a constant sliding velocity of 0.1 m/s and normal loads of 1, 2 and 5 N were used. The static counterparts employed during the test were 6 mm diameter balls made of AISI 52100. For comparison, the wear behavior of the uncoated alloy is also reported. The depth corresponding to the maximum Hertzian shear stress, tmax, achieved for each load was related to the wear performance of the coating. It was shown that the coated alloy presented an improved wear resistance only when the wear tests were performed at normal loads as low as 1 and 2 N. In this case, the material from the static counterpart was transferred to the surface of the coated discs. When higher normal loads of 5N were used, the wear constant achieved an average value of nearly 60% higher when compared to the wear constant value corresponding to the uncoated material. This lower wear resistance was mainly due to the fact that the coating could not stand the applied pressure and fracture, producing a high amount of abrasive debris which contributed to the abrasion of the substrate.