Friction, Wear, and Lubrication; Effects & Modeling

Wednesday, May 1, 2013 2:10 PM in Room Golden West

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2:10 PM E1-3-1 Tribological Behavior of Multilayered Ti-Si-B/Zr-based Thin Film Metallic Glass Coatings with Various Si Contents
Hsien-Wei Chen, Yu-Chen Chan (National Tsing Hua University, Taiwan, Republic of China); Jyh-Wei Lee (Ming Chi University of Technology, Taiwan, Republic of China); Jenq-Gong Duh (National Tsing Hua University, Taiwan, Republic of China); JasonShian-Ching Jang (National Central University, Taiwan, Republic of China)
This study aimed to investigate the Si effects on wear properties of both monolayered (Zr53Cu30Ni9Al8)100-ySiy and multilayered (TiB2)100-xSix/(Zr53Cu30Ni9Al8)100-ySiy coatings. The periodic (TiB2)100-xSix and (Zr53Cu30Ni9Al8)100-ySiy thin film metallic glass (TFMG) coatings were deposited by radio frequency magnetron sputtering of composite targets including TiB2 and Zr53Cu30Ni9Al8 in an argon atmosphere. The crystallography and chemical state were identified by X-ray diffraction and electron spectroscopy for chemical analysis (ESCA). The structure and surface morphology were studied by scanning electron microscope (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM). It was observed that Ti-Si-B/TFMG with higher Si contents exhibited smoother morphology and lower friction coefficient, respectively. The mechanical properties analyzed by nanoindentation and nanoscratch revealed significant improvements in hardness, plastic deformation resistance, and adhesion for Ti-Si-B/TFMG with Si addition. It was demonstrated that Si incorporation effectively enhanced the coating performance and wear resistance due to structure refinement and self-lubricated characteristic.
2:30 PM E1-3-2 A Simple In-situ Method of AFM Calibration for Tribological Characterization of Ultra-thin Transfer Films
David Burris, Harman Khare (University of Delaware, US)

Solid lubricants are unusual in their ability to provide low friction and wear in otherwise unlubricated sliding conditions. In almost every case, thin (10-100nm) and well-adhered transfer films accompany low friction and wear during dry sliding and there is increasing evidence that the transfer films are responsible for the friction and wear reductions. Further elucidating the role of these transfer films in tribology requires direct studies of their tribological properties. Unfortunately, films of this scale are extremely challenging to probe with forces and contact areas that are sufficiently small to isolate their properties from those of the bulk. While the atomic force microscope is uniquely able to probe tribological surfaces in a wear-free single-asperity contact, instrument calibration challenges have limited the usefulness of this technique for quantitative tribological studies. A number of AFM calibration techniques have been proposed and used, but none has gained universal acceptance due to limitations or significant potential error sources. This paper describes a simple ‘in-situ method’ of calibrating AFM friction coefficients which: (1) allows simultaneous calibration and measurement for a given configuration of the AFM system, thus eliminating tip damage and confounding effects of instrument setup adjustments; (2) is insensitive to adhesion, PSD cross talk, transducer/piezo-tube axis misalignment, and shear-center offset; (3) is applicable to integrated tips and colloidal probes since ‘calibration’ is performed on the very substrate for which the friction coefficient is determined; (4) is applicable to any reciprocating friction coefficient measurement.

3:10 PM E1-3-4 Precession Electron Diffraction Studies to Determine Wear-induced Texture Formation and Grain Refinement in Tribological Coatings and Engineered Surfaces
Hamidreza Mohseni, Jon-Erik Mogonye, Rajarshi Banerjee, Peter Collins, Thomas Scharf (University of North Texas, US)
Transmission electron microscopy (TEM) coupled with selected area electron diffraction are capable of identifying nanoscopic phases in tribological contacts. However, interaction of the TEM’s high energy electron beam with the specimen can potentially cause non-systematic dynamic scattering and lead to an uneven distribution of the diffracted intensities. This severely limits the reliability of the nanostructural analysis. In addition, electron backscatter diffraction (EBSD) cannot resolve orientation and texture of tribologically-induced near surface ultrafine grain (<50 nm) structures. To circumvent these issues, precession electron diffraction (PED) was used in conjunction with TEM to investigate worn solid lubricants, such as Laser Engineered Net Shape (LENS) deposited graphite in a TiC/Ni matrix, and engineered surfaces, such as LENS nitrided Ti alloys (α+β Ti-6Al-4V, Ti64 and β Ti-35Nb-7Zr-5Ta, TNZT). In the case of the graphite/TiC/Ni composite, low friction (µ~0.1) was observed with the presence of amorphous carbon (a-C) on the surface with texture evolution in (010) Ni elongated grains, while higher friction was due to the absence of a-C. For the Ti-alloys, nitrided Ti64 exhibited brittle fracture (shear bands) while the nitrided TNZT exhibited plastic deformation (nanocrystalline grain refinement). Precession–orientation imaging phase maps were used to determine the orientation and percentage of α and β-Ti in nitrided TNZT on the surface and sub-surface regions responsible for improved friction and wear.
3:30 PM E1-3-5 Dry Friction Between Laser-patterned Surfaces: Role of Alignment and Structural Wavelength
Andreas Rosenkranz, Carsten Gachot (Saarland University, Germany); Nikolay Prodanow, Martin Mueser (Supercomputing Centre Juelich); Frank Muecklich (Saarland University, Germany)

Friction and related tribological phenomena play a decisive role in technological systems. For many years, a lot of research groups have sought to understand the origin of friction and to enhance the tribological performance of rubbing surfaces. The ability to modify frictional forces on different scales is of utmost importance. There are several techniques that offer the possibility to tailor the contact area thus leading to an improvement in the tribological behaviour. The laser interference metallurgy (LIMET), which is one possible approach of laser surface texturing, is used to produce a well defined surface topography with line-like pattern on both contacting surfaces. Commercial stainless steel and titanium samples were irradiated with a high power pulsed solid state laser (pulse duration of 10 ns and wavelength of 355 nm). The laser experiments were performed using a two beam interference configuration resulting in line-like patterns with three different structural wavelengths. Furthermore, a detailed study of the chemical and microstructural state before and after laser texturing was conducted. The tribological testing was done using a ball on disk configuration (ball material: 100Cr6 steel) in linear oscillating test conditions. In order to control the involved contact geometries and the frictional response, both contacting bodies were structured with the same structural wavelength.

The tribological tests demonstrate that the LIMET is a powerful tool to create a well defined surface topography and to design the contact area of rubbing surfaces. Furthermore, it can be stated that depending on the relative alignment and the structural periodicity, geometrical interlocking between the contacting bodies is possible thus leading to modified frictional properties and enhanced run-in behaviour. It could be shown that dry friction between two laser-patterned solids depends not only on the wavelength of the structuring but also on the relative orientation between the patterns.

3:50 PM E1-3-6 Influence of Aspect Ratio of Silicon Patterned and Coated Surfaces on Wetting and Tribological Characteristics
Shuxue Piao, Nagaraj Machavallavan (KIST, Republic of Korea); Kyung-Young Jhang (Hanyang University, Republic of Korea); Eui-Sung Yoon (KIST, Republic of Korea)
Technologically, majority of the MEMS/NEMS devices which are made out of silicon based materials have inferior tribological characteristics. The present work investigates the influence of aspect ratio on wetting and tribological characteristics of silicon patterned surfaces. Silicon surfaces were photo-lithographically patterned on circular pillar patterns with diameter of 3 µm, pitch of 6 µm, and different aspect ratio ranging from 0.06 to 8.33. Also, patterned silicon surfaces are modified with thin film layer of low surface energy materials such as PTFE to observe its secondary effect. First, wetting behavior of all patterned samples is characterized using Water Contact Angle measurement (WCA). Secondly, Tribological behavior is characterized using Atomic Force Microscopy. We observed that WCA of silicon patterned surfaces under low aspect ratio is decreased with roughness factor, which is good agreement with the Wenzel prediction. Wetting characteristics is changed with the aspect ratio. In case of hydrophobic PTFE surfaces, their trend follows Wenzel prediction. Tribological studies show that there is not much difference in adhesion & frictional behavior although aspect ratio and roughness factor of surfaces are varied. It is explained based on concept of contact area. Our experimental observations show that thin film layer of PTFE coating enhances the hydrophobicity & tribological characteristics of silicon surfaces.
4:10 PM E1-3-7 Laser Interference-induced Microstructural Architectures and Topographies in Gold Thin Films and their Effect under Dry Sliding Conditions
Carsten Gachot, Andreas Rosenkranz, Frank Muecklich (Saarland University, Germany)

Numerous electrical contacts worldwide are exposed to sliding motion. Commonly conductor materials are gold and copper. Very often, electrical contacts are gold plated.

A basic understanding of the fundamental aspects during film growth and methods for a subsequent optimization or tailoring of the film microstructure and surface topography is absolutely essential for improving the physical properties of the as-deposited films. Independent of the deposition technique used (e.g. sputtering or electron beam evaporation), metallic thin films exhibit an amorphous or a polycrystalline microstructure when deposited under typical conditions, such as no or only a moderate substrate heating. In the latter case, films are mainly characterized by a logarithmic normal grain size distribution with randomly oriented grains. As far as technical applications are concerned, microstructural randomness leads to highly inhomogeneous and non-optimized device characteristics. Consequently, circumventing the random grain alignment by a laser-interference induced recrystallization for example with specified threshold energies results in a control of nucleation sites and grain orientations and thus superior properties.

In this context, gold thin films with a nominal thickness ranging between 300 and 700 nm were deposited on Si-substrates by electron beam evaporation. Subsequently, the as-deposited films were laser-patterned by a novel interference technique allowing for long-range ordered and periodic grain architectures and topographies (e.g. line-, dot- and cross-like patterns) on the micron-scale. Depending on the used laser energy density and the number of interfering laser beams, novel engineered microstructures and surfaces appear with beneficial properties.

The resulting tailored gold films were analyzed by high resolution techniques such as electron backscatter diffraction and transmission electron microscopy concerning the microstructure and correlated with thermal simulations. Moreover, detailed studies of the achieved topography after the laser treatment were performed by white light interferometry.

Finally, the results of the sliding tests under dry friction conditions will be presented showing a 40 % reduction of the friction coefficient and an enhanced wear resistance compared to the pristine sample state. Additionally, a Greenwood-Williamson approach is used to explain the tribological findings.

4:30 PM E1-3-8 Stress Analysis of WS2 Coatings Using Scratch Testing and Raman Spectrocopy
Johans Restrepo (Universidad Nacional Autónoma de México, Mexico); JuanManuel Gonzalez (Universidad Del Valle, Colombia); Stephen Muhl (Universidad Nacional Autónoma de México, Mexico); Federico Sequeda (Universidad Del Valle, Colombia)
Tungsten disulphide coatings were deposited using a magnetron sputtering technique at different voltage biases. The films were characterized by X-ray diffraction, perfilometry and Nanoindentation. The tribological properties of the coatings were evaluated using scratch testing without causing severe cracking or total spallation, using two counter materials (1/16” balls of 100CR6 and Al2O3). To study the plastic deformation caused by the application of load during the scratch measurements we used 3d profilometry. Finally, micro-Raman spectroscopy was employed to study any deformation-induced chemical reaction with the ball at different loads for both coating materials. The results showed that the contact pressure caused a lattice deformation in the tungsten disulphide coatings with both type of test balls, but this deformation was larger for the Al2O3 balls. The Raman analysis showed that with the 100CR6 steel balls an oxide layer was formed whilst no such layer was observed for the Al2O3 balls. Finally, optical microscopy and Raman analysis of the two types of balls was performed to investigate the details of the tribological phenomenon that occurred during the scratch testing.
4:50 PM E1-3-9 Investigation of the Tribological Behavior of Electrocodeposited Ni-MoS2 Composite Coatings
Ebru Saraloglu Guler, İshak Karakaya (Middle East Technical University, Turkey); Erkan Konca (Atilim University, Turkey); Abdullah Ozturk, Metehan Erdoğan (Middle East Technical University, Turkey)

Molybdenum disulfide is regarded as one of the most widely used so lid lubricants. One of the application methods of MoS2 on substrates is the electrodeposition in metal matrix. Ni–MoS2 composite coatings were developed on AISI 304 stainless steel substrates by electroplating from Watts bath containing suspended MoS2 particles. The effects of three types of surfactants; depramin C, ammoniumlignosulfonate, sodiumlignosulfonate and the MoS2 concentration on the tribological behavior and particle distribution of electrocodeposited Ni-MoS2 composite coatings were studied by pin on disc tribometer and a scanning electron microscope. Addition of 10 g/l MoS2 (1.2 micron average particle size) into the Watts bath, decreased the friction coefficient of nickel coatings from 0.75 to 0.45. The use of sodiumlignosulfonate and ammoniumlignosulfonate were more effective in homogenously distributing MoS2 particles in nickel matrix and reducing the friction as compared to Depramin C. Moreover, increasing the MoS2 content to higher levels caused further reductions in the friction coefficient.

5:10 PM E1-3-10 Fretting Wear Behaviour of Ti-TiC Composite Alloys: Influence of the TiC Concentration
Jeremy Duhart, Siegfried Fouvry (Ecole Centrale de lyon, France)
Metal matrix composites (MMCs) based with aluminium alloys are widely used in aeronautical industries, for small loading and low temperatures conditions. Different studies confirm that the wear resistance of aluminium alloys, reinforced with SiC particles, is improved significantly due to particle addition [1]. However these aluminium composites are no longer convenient for severe stressing and temperature conditions like observed in engine parts. New material structures involving titanium matrix reinforced with TiC particles have developed to palliate such limitations. These composites are realized by powder metallurgy, which have considerable potential for use in aerospace applications due to their high specific mechanical properties [2].

In this study, three composites, titanium grade 2 based with different particle rates, were tested under fretting wear conditions. The fretting wear analysis was performed under gross slip regime, for several pressures and sliding conditions. Both friction and wear rates responses have been investigated. Like for aluminium composite, it is shown the TiC particle concentration highly influences of the wear resistance. Various hypothesis including oxidation mechanisms and micro-cracking of TiC particules are discussed.

[1] R.N. Rao, S. Das; Materials and Design 31 (2010); 1200–1207

[2] D.B. Miracle, Compos. Sci. Technol. 65 (2005) 2526–2540