ICMCTF2002 Session E1-1: Reduction of Friction Through Coating/Surface Modification

Tuesday, April 23, 2002 8:30 AM in Room California

Tuesday Morning

Start	Invited?	Item
8:30 AM		E1-1-1 Structure and Tribological Properties of Molybdenum Disulphide Multilayer Films J.E. Krzanowski, A.R. Phani (University of New Hampshire); J.J. Nainaparampril (Systran, Inc.) Multilayer films of MoS₂/Ti, MoS₂/C and MoS₂/TiC have been deposited by pulsed laser deposition (PLD). The structural and tribological properties of these films have been studied using x-ray diffraction, x-ray photoelectron spectroscopy and scanning and transmission electron microscopy. Characterization of the MoS₂/Ti and MoS₂/TiC films revealed the absence of a layered structure despite the sequential deposition of the constituent compounds, and x-ray diffraction could only detect the presence of MoS₂. For the MoS₂/C multilayers, a distinct layered structure could be observed in SEM cross-section images. The tribological properties of these films were tested using a pin-on-disk test machine in an air environment containing 45% relative humidity. The multilayer films generally exhibited superior performance in comparison to MoS₂ alone, with friction coefficients as low as 0.05.
8:50 AM		E1-1-2 Analysis of Sputter Deposited W-S Coatings in the Presence of Gaseous Ar, Ar+N₂, and/or Ti Filtered Arc Plasmas A.K. Rai, S.J. Dixit, R.S. Bhattacharya (UES, Inc.) It has been shown recently that the life of cutting tools in certain machining operations can be increased by using a soft low friction coefficient coating such as MoS2 or WS2 on top of a hard coating. Ideally, one would expect to achieve better results by producing a graded coating instead of a layered hard-soft coating. However, this would require the deposition of both hard and soft coatings simultaneously. Generally soft coatings are deposited under different deposition conditions than hard coatings. Thus it is essential to study the characteristics of soft coating under the deposition conditions and technique used for depositing hard coating. In the present work we have utilized a large area filtered arc deposition system (LAFAD) where soft and hard coatings can be deposited respectively by magnetron sputtering and filtered arc techniques. In particular, we have studied the friction and chemical composition of the soft WS2 coating deposited by sputtering in the presence of various gaseous (Ar and Ar+N2) and metal (Ti) filtered arc plasmas. Pin-on-disc technique was used to determine the friction coefficient and Auger electron spectroscopy was utilized to determine the chemical composition of the coatings. The relationship between deposition conditions and coating characteristics has been correlated. It was found that the friction coefficient goes up with increase in the nitrogen content in the coating. Based on the observed data a different approach of depositing hard-soft coating is proposed.
9:10 AM		E1-1-3 MoS₂-Ti Composite Coatings Deposited by Closed-Field Unbalanced Magnetron Sputter Ion Plating: Mechanical-Tribological-Structural Characterization I. Efeoglu, E. Arslan, F. Bulbul (Ataturk University, Turkey) A closed field unbalanced magnetron sputter ion plating (Teer-CFUBMSIP/550) system has been used for the deposition of MoS₂Ti composite coatings on different types of substrate. The mechanical and tribological properties of MoS₂Ti coated composites onto six types of (D2, M2, 440C, 4140, 52100, and 304) steel substrates were characterized using microhardness test, friction-wear test under atmospheric conditions and dry nitrogen. Structural analysis was pointed out using X-ray diffraction and SEM-EPMA. The properties of coatings were improved by selecting the deposition parameters with using Taguchi Method.
9:30 AM	Invited	E1-1-4 Modification of Contact Surfaces by Fullerene-like Solid Lubricant Nanoparticles L. Rapoport, V. Leshchinscky, Yu. Volovik, O. Nepomnyashchy (Holon Institute of Technology, Israel); R. Tenne (Weizmann Institute of Science, Israel) In the past few years, WS₂ and MoS₂ nanoparticles (IF) have been synthesized in the Weizmann Institute. It has been established that IF-WS₂ nanoparticles mixed in oil appear to enhance the tribological properties in definite loading range in comparison to typical metal dichalcogenides. The slippery nature of IF nanoparticles leads to their fast displacement from the contact area, and consequently the efficacy of their lubrication is maintained so long as they can be replenished to the contact area. By confining the IF nanoparticles inside a porous and densified solid matrix, slow release of the nanoparticles onto the metal surface alleviates both friction losses and wear, while assuring the mechanical integrity of the composite. The main goal of this work was to analyze the effects of IF solid lubricant in oil and their impregnation with oil into the porous matrixes on friction and wear of different contact pairs. It was found that impregnation of IF nanoparticles provides the regime of quasi-hydrodynamic lubrication over the widest range of loads in comparison to commercially available solid lubricant. The effect of load and sliding velocity on a stability of the IF nanoparticles is discussed. The results of friction and wear experiments with powdered bronze, iron and iron-nickel parts impregnated with commercially available layered 2H-WS2 particles and IF-WS2 (fullerene-like) nanoparticles are presented. The main advantages of the impregnated IF nanoparticles appeared to be their long-term storage in the porous media, and their subsequent gradual furnishing to the contact surface. The effect of IF on the lubrication regime is explained on the basis of a third-body model. TEM, SEM, XPS and AFM techniques are used in order to evaluate the effect of IF on friction and wear of contact pairs.
10:10 AM		E1-1-6 Mechanisms of Ultra-low Friction by Inorganic Fullerene-like MoS₂ Nanoparticles L. Cizaire, B. Vacher, T. Le-Mogne, J.M. Martin (Ecole Centrale de Lyon, LTDS, France); L. Rapoport (Holon Institute of Technology, Israel); A. Margolin, R. Tenne (Weizmann Institute of Science, Israel) Inorganic Fullerene-like (IF)-MoS₂ nanoparticles were tested under boundary lubrication and ultrahigh vacuum (UHV) and were found to give an ultra-low friction coefficient in both cases compared to hexagonal (h)-MoS₂ material. Previous works made by L.Rapoport et al. with IF-WS₂ ¹ reveal that the effect of the inorganic fullerene-like materials decreases at high loads and sliding velocities. Nevertheless, under the conditions used in our experiments, with high pressure (maximum pressure above 1.1 GPa in oil and 400 MPa in high vacuum) and slow sliding velocities (1.7 mm/s in oil test and 1mm/s in high vacuum), friction decreases and stabilizes at about 0.04 for 800 cycles in both cases. Therefore, IF-MoS₂ material appears to be a good candidate for use in various environments in regards to other structural MoS₂ forms. Wear mechanisms were investigated using both High Resolution TEM and surface analyses (XPS) on the wear tracks. Wear particles collected from the flat wear scar show several morphologies, suggesting at least two lubricating mechanisms. As the spherical particles are found in the wear debris, rolling may be a predominant event. However, flattened IF-MoS₂ particles are often observed after friction. In this case, low friction is thought to be due either to sliding between IF-MoS₂ external planes or to slip between individual unwrapped sheets ^2,3,4. ¹ (a). L. Rapoport et al., Nature, 387, 791 (1997). (b). L. Rapoport, Y. Feldman, M. Homyonfer, H. Cohen, J. Sloan, J. L. Hutchison, and R. Tenne, Wear 975-982 (1999). ² C. Grossiord, J. M. Martin, T. Le-Mogne, and T. Palermo, Surface and coatings technology 352, 108-109 (1998). ³ C. Grossiord, J. M. Martin, T. Le-Mogne, K. Inoue, and J. Igarashi, Journal of vacuum science and technology, (1998). ⁴ C. Grossiord, K. Varlot, J. M. Martin, T. Le-Mogne, C. Esnouf, and K. Inoue, Tribology International, (1998).
10:30 AM		E1-1-7 Performance of CrN/MoS₂(Ti) Coatings for Stamping Dies S. Carrera (Colorado School of Mines); O. Salas (ITESM, Mexico on sabbatical to Colorado School of Mines); J.J. Moore (Colorado School of Mines); D. Bell (Phygen Inc.) A CrN/MoS₂(Ti) coating was developed in order to improve the tribological characteristics of single CrN coatings for stamping operations. The MoS₂(Ti) coating was produced by PVD closed field unbalanced magnetron sputtering on CrN coated stainless steel substrates. The tribological performance of both, the single CrN coating and the CrN/MoS₂(Ti) coating was evaluated and compared. Characterization of the coatings included: scratch testing, wear testing, nanoindentation, x-ray diffraction, optical and scanning electron microscopy.
10:50 AM		E1-1-8 Mechano-Chemical Method for Tribological Coating A. Torosyan (Institute of General and Inorganic Chemistry, National Academy of Sciences of Armenia); A.M. Korsunsky (University of Oxford, United Kingdom); K.G. Kazarian (National Academy of Sciences of Armenia) We describe improved tribological properties of the systems obtained using our new mechano-chemical method for the syntheses of sulfide coatings MoS2 and WS2. The new method leads to decreased friction coefficients and increased durability of coatings. Optimal conditions of mechano-chemical synthesis were found experimentally. At hypo-optimal concentrations of sulfur the coating contains numerous flaws and cracks, while at hyper-optimal quantities of sulfur the surface quality deteriorates and roughness is increased. When key synthesis parameters are maintained in the optimal window the process of synthesis is well-controlled and reproducible, and thickness of the coating can be regulated. Plane samples of low carbon steel and bearing steel balls were mechano-chemically coated with Mo-MoS2 and W-WS2 layers. The properties were tested using a pin-on-disc wear tester. Testing was carried out under contact pressure P=300-350 Mpa and sliding speed of 0.8m/s, corresponding to extreme wear conditions. Control parameters for testing were friction coefficient f and the durability C, defined as the number of cycles before coating failure. The results are given below to compare the performance of the mechano-chemical coatings with conventional vapor phase deposited coatings, in the form (Method of Synthesis: Fric. coeff. f - No. cyc. to failure) (Treatment of Mo in H2S: 0.05 - 30000) (Treatment of Mo in S vapor: 0.05 - 50000) (Mechano-chemical Mo-MoS2: 0.03 - 70000). Mechano-chemical coating allows appreciable improvement of tribological properties of coatings for severe operating conditions. The novel deposition method is carried out at room temperature from initial elemental substances, and the coatings are synthesized under the regime of dry friction and impact, so that they develop micro- and macro-structures already well adapted for conditions of severe contact loading, require minimal â€˜running-inâ€™ and display stable wear from the start.
11:10 AM		E1-1-9 Performance and Limitation of MoS₂/Ti Composite Coated Inserts Tested for Dry, High Speed Milling and Turning of Steel and Grey Cast Iron N.M. Renevier (Teer Coatings Ltd., United Kingdom); H. Oosterling (TNO Institute of Industrial Technology, The Netherlands); U. Koenig (Widia GmbH, Germany); H. Dautzenberg, B.J. Kim (Technical University Eindhoven, The Netherlands); L. Geppert (Niles Simmons, Germany); J.M. Koopmans (Unisign B.V., The Netherlands); J. Leopold (FhG-IWU, Germany) Self-lubricant - Low friction MoS₂ / Ti (MoST) composite coatings (PVD magnetron sputtering) [1] has been deposited onto hard coating (PECVD) carbide inserts and have been tested for machining dry high speed milling and turning of steel and grey cast iron. Dry machining (DM) is an important objective in machining industry to reduce environmental- and production costs. DM using MoST is possible in some cases: because of the low friction, the use of coolant is not necessary. Also better chip evacuation and a smoother cutting process will occur, which can lead to higher accuracy of products. The paper includes an assessment of the limiting factors for a successful machining performance of coated tools including the influence of the geometry of the tool, the machining parameters. These factors mentioned above have been correlated to the mechanical, chemical, oxidation and structural behaviour of the tools during machining tests. [1] N.M Renevier, V.C Fox, D. G Teer, J. Hampshire, Surf. Coat. Technol., 127 (2000) 24
11:30 AM		E1-1-10 Microstructure and Tribological Properties of Plasma-sprayed Chromium Oxide-molybdenum Oxide Composite Coatings I.W. Lyo, H.-S. Ahn (Korea Institute of Science and Technology, Korea); D.S. Lim (Korea University, Korea) Plasma-sprayed Cr₂O₃-based coatings containing MoO₃ were studied to gain a better understanding of the influence of molibdenum oxide composition in the coatings on their tribological behaviour. Cr₂O₃/MoO₃ composite powders and a Cr₂O₃ powder were fabricated using a spray-drying method and plasma-sprayed coatings of these powders were produced. Wear tests were conducted with a reciprocating motion at room temperature and 450°C under dry sliding condition. Measurement of friction coefficient was made in association with the sliding cycle. The physical characteristics of surfaces was investigated by scanning electron microscopy and chemical composition of the coating surfaces was analyzed using a X-ray photoelectron spectrometer and a transmission electron microscopy. The study showed that the micro-hardness of coatings containing MoO₃ were higher than that composed of Cr₂O₃ alone. The result of TEM analysis indicated that chromium/molybdenum was precipitated in the grain and grain boundary. The friction coefficient of the MoO₃-added coatings were lower than that without MoO₃ addition at both test temperatures. However, the addition of MoO₃ in the Cr₂O₃ coatings did not significantly improve the anti-wear performance of the coatings at both test temperatures. Dispersed smooth films were formed in the worn surface for all coatings. These wear protecting layers, formed by plastic deformation of adhered and compacted debris particles to the surface, strongly influence the friction of the coatings as already observed by the authors with different plasma-sprayed coatings. The chemical composition of these films varied depending on the test temperature.
11:50 AM		E1-1-11 The Cutting performance of PVD-coated Tools in Dry Machining H.K. Toenshoff, H.K. Tönshoff, T. Friemuth, C. Podolsky, A. Mohlfeld (University of Hannover, Germany) Today, special research activities are concentrated on the optimization of coating properties to improve the performance of cutting tools. (Ti,Al)N-based hard coatings are well known for their excellent microhardness even at elevated temperatures as well as for their good oxidation and wear resistance. Further improvements concerning the wear behaviour may be achieved by reducing the friction between tool and workpiece material in cutting. In this paper, the cutting performance of hard and soft PVD-coated carbide tools is investigated in turning and drilling of tempered steel. Chip structure is analyzed in order to investigate the effect of friction. The cutting forces and the wear behaviour of the drilling process are highlighted for (Ti,Al)N and (Ti,Al)N+ a-C-coatings. A superior wear behaviour of soft coated tools was found in the initial wear phase. An influence of soft coatings on the wear behaviour after the running-in period could not be observed.