Future Needs for Tribo-Corrosion Research and Testing

Tribo-corrosion is an emerging interdisciplinary subject that spans from basic research on the behavior of surfaces in mechanical contact in chemically active surroundings to the test methods needed to quantify its effects, and from the selection of materials for bio-implants to the minimization of surface degradation and wastage in advanced energy conversion systems. Such a diverse field brings with it many challenges in understanding, testing, standardization, and application to engineering practice. This paper summarizes a panel discussion and participant survey held at the Third International Symposium on Tribo-Corrosion in Atlanta, Georgia, USA, in April 2012. It reflects a sense of agreement on many of the key scientific challenges in the field and the fact that tribo-corrosion is still in its infancy in terms of broad industry recognition, education, and the ability of those who conduct tribo-corrosion research to connect their laboratory results and theories to applications. Some sub-fields, notably the bio-tribo-corrosion of medical implants, have witnessed active international research efforts, but the engineering community in many other important areas of technology may not yet be aware of the field despite numerous tribo-corrosion problems that may exist within their purview

Photon-Photon Luminosities in Relativistic Heavy Ion Collisions at LHC Energies

Effective photon-photon luminosities are calculated for various realistic hadron collider scenarios. The main characteristics of photon-photon processes at relativistic heavy-ion colliders are established and compared to the corresponding photon-photon luminosities at electron-positron and future Photon Linear Colliders (PLC). Higher order corrections as well as inelastic processes are discussed. It is concluded that feasible high luminosity Ca-Ca collisions at the Large Hadron Collider (LHC) are an interesting option for photon-photon physics up to about 100 GeV photon-photon CM energy.Comment: REVTeX, 13 pages, 10 figures (uuencoded,compressed postscript

Discovering the constrained NMSSM with tau leptons at the LHC

The constrained Next-to-Minimal Supersymmetric Standard Model (cNMSSM) with mSugra-like boundary conditions at the GUT scale implies a singlino-like LSP with a mass just a few GeV below a stau NLSP. Hence, most of the squark/gluino decay cascades contain two tau leptons. The gluino mass >~ 1.2 TeV is somewhat larger than the squark masses of >~ 1 TeV. We simulate signal and background events for such a scenario at the LHC, and propose cuts on the transverse momenta of two jets, the missing transverse energy and the transverse momentum of a hadronically decaying tau lepton. This dedicated analysis allows to improve on the results of generic supersymmetry searches for a large part of the parameter space of the cNMSSM. The distribution of the effective mass and the signal rate provide sensitivity to distinguish the cNMSSM from the constrained Minimal Supersymmetric Standard Model in the stau-coannihilation region.Comment: 18 pages, 3 Figure

Tribological testing - Intelligent test selection using the tribological aspect number

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Bridging the gap: the need for microtribology test equipment

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Friction of thin coatings on three length scales under reciprocating sliding

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Investigation of friction at µN and mN force range on hard coatings

In recent years 'low load' tribology has received more attention due to the emergence of special devices like MEMS, and new materials such as bioimplants, polymers and textured surfaces. The tribological characterization of MEMS materials is challenging, because the devices operate at nominal contact pressures of only a few MPa and low wear rates of nm/hr. In this work, the friction and wear behavior of the commonly used industrial coatings titanium nitride (TiN) and diamond-like carbon (DLC) are investigated with normal forces in between Newton (conventional tribology) and nanoNewton (nanotribology). As the applied normal force reduces from mN's to µN's, the effect of surface roughness becomes strikingly apparent in the recorded tangential force. The friction of TiN coating appears to be less sensitive to surface roughness variations and chemical changes of the countermaterial, than DLC. The behavior of DLC at low contact pressures is different from the well-known low friction behavior of DLC coatings at high contact pressures.status: publishe

Corrosion-wear of passivating materials in sliding contacts based on a concept of active wear track area

The concept of active wear track area is proposed as a way to investigate the mechanism of the corrosion-wear behavior of passive materials under sliding conditions. This active wear track area represents that part of the wear track that looses temporarily its passive character due to the mechanical interaction during sliding. It is shown that the active wear track area can be determined from repassivation kinetics measured on electrochemically activated material by a potential pulse method, and from anodic currents measured during sliding ball-on-disk tests. The use of that concept is illustrated for the case of stainless steel AISI 316 immersed in a 0.5 M H2SO4 solution. At loads below 2 N, no breakthrough of the oxide film is noticed. At loads between 2 and 12 N, the corrosion-wear agrees well with Quinn's mild oxidation wear mechanism. The corrosion-wear of AISI 316 consists then of two processes namely a mechanical delamination of the passive layer in part of the wear track, followed by a progressive electrochemical re-passivation of that active wear track area. The thickness of the passive layer on AISI 316 was derived from the active wear track area and the electrochemical response of passive and active AISI 316 material. A value of 2-3 nm was obtained that agrees well with data obtained by other methods. Above a load of 12 N, the corrosion-wear increases steeply due to a degradation process involving abrasion and/or breakdown of more than just the oxide film. © 2001 Elsevier Science B. V. All rights reserved.status: publishe

Friction and nanowear of hard coatings in reciprocating sliding at milli-Newton loads

The wear occurring at very low normal loads and in very small contacts is of prime interest to the field of nanotribology. Friction and wear phenomena in micro-electromechanical components (MEMS) are not well understood and that limits the development of commercial nano components. In this work, wear and friction at loads in the milli-Newton range was investigated under reciprocating sliding where wear and dissipated energy are in the range of nanometers and microjoules, respectively. Reciprocating sliding tests were performed with a modular microtribometer that was operated at normal forces of milli-Newton. This tribometer bridges the gap between macroscale test equipments and the atomic force microscopes. Nanowear tests were carried out for different test durations on hard coatings like DLC and TiN, with silicon nitride balls as the counterbody. After the reciprocating sliding tests at very low loads, the wear tracks were investigated with an atomic force microscope to observe topographical changes in the wear tracks, and to analyze the nanowear. The importance of AFM for characterizing the nanowear appears clearly from this work. The obtained results are compared with existing theories on friction and wear to observe their validity in low load range. The importance of contact pressure and third body interactions in the wear track is also discussed based on AFM observations.status: publishe