Dynamic nanoscale in situ TEM tribology
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Dynamic nanoscale in situ TEM tribology A J Lockwood1, K Anantheshwara2, M S Bobji2 and B J Inkson1 1 NanoLAB Centre. Department of Materials Science and Engineering, The University of Sheffield, Sheffield, S1 3JD, UK 2 Department of Mechanical Engineering, Indian Institute of Science (IISc), Bangalore, 560012, India ABSTRACT Nanotribology, the study of friction, wear and lubrication at the nanoscale is an important area of research; however in practice due to the size scale, requires specifically designed tools to characterize nanoscale contacts. We have developed a TEM triboprobe incorporating an advanced nano-positioner with 3D programmable motion inside a transmission electron microscope (TEM) which allows us to selectively apply multiple reciprocating wear cycles to a nanoscale surface, and observe in real-time dynamical changes and the evolution of wear around a sliding nano-contact. Nanoscale cyclic rubbing of an automotive aluminum-silicon alloy processed by focused ion beam (FIB) reveals dynamical surface fragmentation and the generation of nanoscale debris particles. The nanoparticles undergo complex motion as they interact with the sliding nanocontact. Over hundreds of reciprocating cycles, frictional heating leads to a phase separation of the Ga+ ions implanted by FIB forming liquid Ga nano-droplets and liquid bridges. The addition of nanoscale debris particles and liquid droplets dramatically changes the wear dynamics and transforms a 2-body sliding contact into a complex 4-body solid–liquid system exhibiting timedependent, non-equilibrium kinetic behavior. TEM nanotribology opens up new possibilities for the real-time quantification of cyclic friction, wear and dynamic solid–liquid nano-mechanics, which will have widespread applications in many areas of nano-science and nanotechnology. INTRODUCTION Wear occurs when two contacting surfaces are moved relative to one another [1]. It is a progressive loss of material resulting in significant surface damage. Material is lost in the form of debris particles which may become trapped between the sliding surfaces before being ejected away from the contact. Whilst these particles remain entrapped, they interact and can determine the wear characteristics of the material. Traditional wear studies look at snap-shots in time of the worn surface and try to deduce the behavior and interaction of the contacts, however without high resolution imaging of the interface throughout the sliding process, this is not simple. We have overcome this problem of a hidden-interface by developing a custom built insitu transmission electron microscope (TEM) triboprobe, which can be programmed to perform reciprocating wear experiments whilst simultaneously imaging the sliding contacts at high resolution. This significant development will impact on the understanding of nano- and microscale tribological behavior of many systems, including wear resistant coatings, nanoparticle lubricants and micro-devices with contacting and rubbing parts such as micro-electromechanical systems (MEMS) mot
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