ICMCTF2010 Session E1-2: Friction and Wear of Coatings: Lubrication, Surface Effects and Modeling

Friday, April 30, 2010 8:00 AM in Room Pacific Salon 1
Friday Morning

Time Period FrM Sessions | Abstract Timeline | Topic E Sessions | Time Periods | Topics | ICMCTF2010 Schedule

Start Invited? Item
8:00 AM E1-2-1 Microstructure and Properties Evolution of AlSi Coated Surfaces
Ola Rashwan, Vesselin Stoilov (University of Windsor, Canada)
Aluminum-Silicon alloys are extensively used in automotive applications due to their excellent physical and triobological properties. In this paper, the aluminum silicon alloys, with DLC, CrN and Al2O3 are investigated to determine the threshold fracture load of the whole system under monotonic loading condition. As it is known, the fracture and deboning of the silicon particles under monotonic loading might lead to nucleation, growth, and coalescence of voids, hence, failure of the cast aluminum silicon alloys occurs. Yet, there are a limited number of studies that have been done to study the combined effects of the coating materials, the coating thickness, and the shape of the Si particles, on the threshold fracture load of the aluminum silicon alloys. In this study, finite element analysis has been performed to study the combined effects of the above mentioned parameters on the critical fracture load of the coated aluminum silicon alloys. A cohesive layer has been assumed between the Si particles and Al matrix and the coating layer and the matrix. It was found out that there is no single parameter which affects the fracture and deboning of Si particles, yet it is the combination of different parameters. For example, the Si particle shape plays a major role in determining the critical fracture stress with a circular shape outperforms the elliptical shape. The combination the circular Si particle and the CrN as coating material gives highest critical fracture stress while Al2O3 exhibits very poor performance with elliptical Si particle and outstanding performance circular Si particle. Finally DLC does not perform well with the circular Si particles and it shows the highest possible fracture stress with elliptical Si particles.
8:20 AM E1-2-2 Tribological Properties of CrN/AlN Thin Films Deposited on H13 Steel by Reactive Unbalanced Magnetron Sputtering
A. Rojo (ITESM-TOL, Mexico); J. Solis-Romero (DGEST-ITTLA/ITESM-CEM, Mexico); J. Oseguera-Pena, O. Salis-Martinez (ITESM-CEM, Mexico)

This paper is related to the development of CrN/AlN thin films on H13 tool steel produced with the physical vapor deposition (PVD) process, where the objective was to determine the friction and wear of the layers on this tool steel used for hot work. The films were produced by reactive magnetron sputtering of aluminum under s everal modes of injection of nitrogen to find the optimum deposition conditions to form a satisfactory structure such that it provided a good adhesion to the substrate. The injection methods used were: convectional injection of Ar + N2 mixture away from the substrate varying the amount of nitrogen, Ar + N2 mixture away of the substrate with extra nitrogen near the substrate and direct injection of N2 near the substrate. The injection method that results in a richer nitrogen atmosphere seems to produce better outcomes. The resulting coatings were characterized by X-ray diffraction (XRD), scanning electron microscopy equipped with energy dispersive X-ray micro analysis (SEM-EDS) and their tribological characterization was carried out by using a pin-on disk tribometer.

8:40 AM E1-2-3 Influence of the Nitriding and TiAlN/TiN Coating Thickness on the Sliding Wear Behavior of Duplex Treated AISI H13 Steel
Ricardo Torres, Paulo Soares (Pontifícia Universidade Católica do Paraná, Brazil); Cleomar Schmitz, Carlos Siqueira (Universidade Federal do Paraná, Brazil)
AISI H13 die steel substrates were low pressure gas nitrided in three different nitriding cases, named case A, B and C. The nitrided cases hardness was assessed by instrumented indentation. In the nitriding case A, the surface hardness was around 12 GPa and the nitriding thickness was around 40 µm. In the nitriding case B, the surface hardness was the same as in case A, but the nitriding thickness was around 70 µm. Finally, in the nitriding case C, the nitriding thickness was the same as in case B, but the surface hardness was around 14 GPa. XRD analyses and optical microscopy results showed that the nitriding cases microstructure was composed mainly by the diffusion layer with small amount of Cr2N precipitates. Nitrided and non nitrided samples were subsequently coated with TiAlN/TiN system in two total thicknesses: 3 and 7 μm. The deposition process was carried out in a cathodic arc evaporation facility. Finally, sliding experiments were conducted in a linearly reciprocating ball-on-flat tribometer. The sliding tests were performed using a 16Cr6 steel ball, the tests speed was 3.14 cm/s and the tests load was 1N. All the wear tracks produced during the sliding tests showed iron adhesion. Moreover, the friction coefficient of the duplex treated surface is highly influenced by the characteristics of the nitrided surface. The TiAlN/TiN over nitrided case A showed the lowest friction coefficient. TiAlN/TiN thickness does not play a major role in the friction coefficient of TiAlN/TiN over the nitrided cases. On the other hand, TiAlN/TiN thickness does change the friction coefficient of the non nitrided H13 specimens. It was observed that the friction coefficient of a 7 μm TiAlN/TiN is lower than a 3 μm TiAlN/TiN over non nitrided specimens.
9:00 AM Invited E1-2-4 Polymer Monolayers as Lubricious Coatings
Nicholas Spencer (ETH Zurich, Switzerland)

Nature lubricates with polymer monolayers: The substrates are soft, the base lubricant is water, and the polymers are glycoproteins. Glycoproteins consist of a proteinaceous backbone with oligosaccharide side chains, and it is these latter structures that appear to lead to the lubricious behavior of the glycoprotein-covered surface.

Lubricating man-made devices with glycoproteins is not very practicable. They are expensive to obtain in quantity, and susceptible to bacterial attack. They are also not suited to the lubrication of many surfaces, especially those of hard materials. Nevertheless, some of the natural principles can be utilized for the design of lubricating polymer systems that can work in a variety of environments on a variety of substrates.

The majority of studies carried out in our laboratory have concerned aqueous lubricant systems. Water is rarely used at present as a lubricant in an industrial environment, but the combination of novel polymer additives with corrosion resistant sliding surfaces, such as engineering polymers or ceramics (e.g. Si3N4), could lead to the introduction of a new generation of oil-free bearing systems. The common factor in the polymer monolayers appled to date is that they have been surface tethered, like the oligosaccharides in nature, often leading to the formation of brush-like structures upon exposure to a "good" solvent. Polymer brushes have a variety of interesting applications in many different technologies, and their fabrication is either carried out by attaching ready-made polymers to the surface by one end ("grafting to"), or by immobilizing initiators on the substrate and then growing polymer chains out of the surface ("grafting from"). Both approaches have been utilized in our laboratories and have been shown to lead to substantial friction reduction under aqueous lubrication.

Water has a major drawback as a lubricant, in that its viscosity is essentially pressure independent. This results in poor performance under classical EHL conditions, as encountered in traditional ball bearings, for example. Two approaches can mitigate this situation: the use of elastomeric contacting surfaces, such that the soft EHL regime is encountered, and the addition of a viscosity-enhancing fluid, such as glycerol, to the water. The latter approach has the advantage that the transition to mixed and hydrodynamic lubrication happens at a lower speed, leading to a lower friction coefficient over a wider range of conditions. The pressure coefficient of viscosity of glycerol, being greater than that of water, also brings with it additional benefits.

9:40 AM E1-2-6 On the Relationships Between the Fretting and Ball Cratering Behaviors of Solid Lubricant Coatings
Vincent Fridrici (Ecole Centrale de Lyon - LTDS, France); Dabing Luo (Ecole Centrale de Lyon - LTDS & Southwest Jiaotong University, France); Philippe Kapsa (Ecole Centrale de Lyon - LTDS, France)
Employing solid lubricant coatings to reduce friction is one of the most effective methods to mitigate fretting damage. However, facing numerous available coatings, users often feel confounded, and the selection of the optimum coating for a specific application is still a tough task. Some simple methods are expected to help the selection. Ball cratering as a promising technique is becoming popular in the developing process of new coatings to assess their abrasion resistance. The objective of this paper is to identify the relationships between the fretting behavior and the ball cratering resistance of coatings, and attempt to use ball cratering to pre-select coatings for fretting conditions in order to cut down the number of candidate coatings and shorten the fretting tests. In this study, several bonded solid lubricant coatings, principally based on PTFE or MoS2, were investigated by ball cratering and fretting tests. The results showed that the coatings in ball cratering presented similar tribological performance as in fretting tests in terms of endurance and wear resistance, i.e., the coatings with good ball cratering resistance also exhibited long lifetime in fretting tests, so ball cratering can be considered as a simple test to pre-select solid lubricant coatings for fretting applications.
10:00 AM E1-2-7 Temperature Effects on the Wear Behavior of Molybdenum Disulfide Solid Lubricant Films
Rachel Colbert, James Keith, W.G. Sawyer (University of Florida)
The space environment, with high vacuum conditions (1x10-6 Torr) and a wide thermal range (T>200ºC or T<0ºC), is one of the most difficult tribological environments in which to operate. These environmental conditions have led to the use of thin solid films to prevent seizure of many joints which include highly loaded restraints and hinges. The solid lubricant thin films primarily used are molybdenum disulfide (MoS2) based, but the tribological performance of these MoS2 films under space relevant conditions remains largely unquantified. This study examines the effects of temperature on the wear rate and debris size of MoS2 films in high-vacuum environments. We find that the debris size increases by a factor of 5 over a temperature range from -100°C to 100°C.
10:20 AM E1-2-8 Tribological Properties in Different Test Conditions of Thin Films TiTaBN Deposited by CFUBMS
Ozlem Baran (Erzincan University, Turkey); Ihsan Efeoglu (Atatürk University, Turkey); Braham Prakash (Luleå University of Technology, Turkey)
TiBN films are used as wear protective coatings for various industrial applications. The mechanical and tribological properties of this coatings varies depend on boron, nitrogen and alloying elements contents. In this study, we investigated machenical and tribological properties of TiTaBN co-sputtered with Ta at the different nitrogen gas flux.TiTaBN films were deposited on D2 steel substrates and silicon wafers by Closed-Field Unbalanced Magnetron Sputtering (CFUBMS). Composition, morphology and structure were analyzed by EDS, SEM, XRD, microhardness tester. Friction and wear properties of this films were determined using a pin-on disc tribo-tester in different test conditions (air,dry nitrogen,distillated water,oil and elevated temperature).
10:40 AM E1-2-9 Comparison of Abrasive Wear Resistance of Low Carbon Steels Subjected to Carburizing, Nitriding, Nitrocarburizing, and Boriding Treatments
Vivekanand Sista (Argonne National Laboratory); Guldem Kartal (Istanbul Technical University, Turkey); Ali Erdemir, Osman Eryilmaz, Gregory Krumdick (Argonne National Laboratory); Servet Timur (Istanbul Technical University, Turkey)

A Calotest micro-abrasion machine (which is used widely to determine the thickness of hard coatings) was used to

perform abrasive wear tests on AISI 1018 steel substrates after a variety of surface treatments such as

carburizing, nitro-carburizing, electrochemical boriding and pack boriding. Using a variety of abrasive slurries

(containing alumina, SiC, and diamond particles), the effects of test duration on the wear resistance of untreated

and surface treated substrates were evaluated and the results were compared in terms of wear crater depths and

the weight losses. Using the present technique, wear resistance of single phase boride layers (Fe2B) for pack

boriding, electrochemical boriding, and double phase boride layers (FeB + Fe2B) formed during electrochemical boriding have been calculated. We found that borided surfaces are much more resistant to abrasive wear than the surfaces that were treated by other methods.

11:00 AM E1-2-12 The Effect of Rhenium on The Tribological Properties of Al-Ti-Re-N and Cr-Re-N Coatings
Zafer Kahraman, Kursat Kazmanli (Istanbul Technical University, Turkey); Ali Erdemir (Argonne National Laboratory); Mustafa Urgen (Istanbul Technical University, Turkey)

In this study, the effects of rhenium on the tribological properties of Al-Ti-N and Cr-N coatings were investigated. The coatings were produced by cathodic arc + magnetron sputtering hybrid physical vapor deposition technique. Al-Ti-N and Cr-N coatings were deposited by using cathodic arc. The arc current and N2 pressure were 80 Amps and 1 Pa, respectively. In order to incorporate rhenium into Al-Ti-N and Cr-N coatings, a rhenium target was simultaneously sputtered with 200 W. The rhenium content of Al-Ti-Re-N and Cr-Re-N were 2.52 at.% and 1.58 at.%, respectively. In order to characterize the coatings, Calotest, X-Ray Diffraction, Scanning Electron Microscopy, EDS and micro hardness techniques were used.

The tribological properties of the coatings were investigated by using ball-on-disc and reciprocating tests against Al2O3 balls at different temperatures starting from room temperature up to 200 °C. The wear of the coatings and the counter body surfaces were observed with 3D optical profilometer and SEM. The wear debris in the wear tracks were analyzed with Micro Raman Spectroscopy. The wear behavior of the coatings were correlated with the chemistry of the compounds formed in the wear track. The interdependent role of temperature and rhenium content on the tribological behavior of the coatings were presented.

Time Period FrM Sessions | Abstract Timeline | Topic E Sessions | Time Periods | Topics | ICMCTF2010 Schedule