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Title: Direct observation of lubricant additives using tomography techniques

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Journal Article: Publisher's Accepted Manuscript
Journal Name:
Applied Physics Letters
Additional Journal Information:
Journal Volume: 109; Journal Issue: 4; Related Information: CHORUS Timestamp: 2016-12-27 18:08:01; Journal ID: ISSN 0003-6951
American Institute of Physics
Country of Publication:
United States

Citation Formats

Chen, Yunyun, Sanchez, Carlos, Parkinson, Dilworth Y., and Liang, Hong. Direct observation of lubricant additives using tomography techniques. United States: N. p., 2016. Web. doi:10.1063/1.4960020.
Chen, Yunyun, Sanchez, Carlos, Parkinson, Dilworth Y., & Liang, Hong. Direct observation of lubricant additives using tomography techniques. United States. doi:10.1063/1.4960020.
Chen, Yunyun, Sanchez, Carlos, Parkinson, Dilworth Y., and Liang, Hong. 2016. "Direct observation of lubricant additives using tomography techniques". United States. doi:10.1063/1.4960020.
title = {Direct observation of lubricant additives using tomography techniques},
author = {Chen, Yunyun and Sanchez, Carlos and Parkinson, Dilworth Y. and Liang, Hong},
abstractNote = {},
doi = {10.1063/1.4960020},
journal = {Applied Physics Letters},
number = 4,
volume = 109,
place = {United States},
year = 2016,
month = 7

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1063/1.4960020

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  • Lubricants play important roles in daily activities such as driving, walking, and cooking. The current understanding of mechanisms of lubrication, particularly in mechanical systems, has been limited by the lack of capability in direct observation. Here, we report an in situ approach to directly observe the motion of additive particles in grease under the influence of shear. Using the K-edge tomography technique, it is possible to detect particular additives in a grease and observe their distribution through 3D visualization. A commercial grease as a reference was studied with and without an inorganic additive of Fe{sub 3}O{sub 4} microparticles. The resultsmore » showed that it was possible to identify these particles and track their movement. Under a shear stress, Fe{sub 3}O{sub 4} particles were found to adhere to the edge of calcium complex thickeners commonly used in grease. Due to sliding, the grease formed a film with increased density. This approach enables in-line monitoring of a lubricant and future investigation in mechanisms of lubrication.« less
  • Atom probe tomography (APT) is used to investigate grain-boundary segregation of W solute atoms in nanocrystalline Ni. For the heat-treated specimens used here, the grain structure can be observed in the APT data, enabling direct composition analyses across individual grain boundaries. These direct measurements are used to validate methods proposed in earlier work, which determine the average segregation state in nanocrystalline materials through statistical analysis of the solute distribution, without knowledge of the boundary positions. Good agreement is demonstrated between the two experimental techniques.
  • The ordered compound Ni/sub 3/Al is potentially useful as a high temperature structural material, since its yield stress increases with increasing temperature up to --650/sup 0/. The major obstacle to the structural use of polycrystalline Ni/sub 3/Al is its tendency to fail intergranularly. The ductility of Ni/sub 3/Al can be improved by the addition of small amounts of boron to a slightly Ni-rich compound. The boron is found to segregate to the grain boundaries, and changes the fracture mode from intergranular to transgranular by a mechanism which is not yet understood. Possible explanations for the presence of a/2<110>-type dislocations are:more » (i) the dislocations are imperfect, with the associated antiphase boundary contrast not visible, or (ii) the Ni/sub 3/Al is disordered in the vicinity of the interface, resulting in a thin layer of f.c.c. material at the boundary, and the dislocations then have the expected f.c.c. Burgers vector. In support of the possibility of disordering are atom-probe field ion microscopy observations which showed that the boundary region is Ni-rich, with deviations from the average alloy composition of up to 5 at % Ni. It is reasonable to predict that the thickness of the disordered layer will be a function of temperature, and so the contribution of the disordered layer to the mechanical properties may also be temperature dependent. It can be speculated that the solubility of boron, and any other impurities that are present, will be different in disordered and ordered Ni/sub 3/Al.« less
  • Precipitation processes under neutron irradiation are of great interest, of course, because of their importance in nuclear industry but, also, from a theoretical point of view. In this scope, prediction and modelling of the property changes of pressure vessel steels under irradiation require a more in depth knowledge of the microstructural evolution; structural and compositional features of formed precipitates being key parameters. One of the main advantages of the new generation of atom probe that was recently developed, namely the Tomographic Atom Probe (TAP), is that a three-dimensional observation of the spatial distribution of solutes (Cu) can be achieved onmore » a near atomic scale. In this work, the very first three-dimensional (3D) images of neutron irradiated FeCu alloys provided by this new apparatus are presented and discussed. These 3D-reconstructions give for the first time, a direct observation of irradiation induced precipitated particles in these model alloys on a subnanometer scale.« less
  • Nickel base superalloys such as the Astroloy have been developed for turbine applications in the aerospace industry. These materials derive their remarkable mechanical properties at high temperatures (700--1,100 C) from the presence of a high volume fraction (50--70%) of ordered Ni[sub 3]Al type [gamma][prime] precipitate dispersed in a [gamma] solid solution. Many additional elements are incorporated in the material in order to strengthen the [gamma] matrix (Mo...) or for corrosion properties (Cr). However, the presence of grain boundaries in alloys may lead to detrimental effects for mechanical properties. The tendency of these materials to fracture intergranularly has been attributed tomore » low grain boundary cohesion. In order to avoid boundary decohesion, minor elements such as boron, carbon or zirconium are added. These elements improve the ductility as well as the mechanical resistance of the material. Since creep failure frequently initiates in grain boundaries, it is of utmost importance to gather information about the local chemistry of grain boundaries. The main goal here is to clarify the role of minor elements in the strengthening effect of boundaries.« less