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Microscopy & microanalysis 2016 in Columbus, Ohio

Microscopy Today

Michael, Joseph R.

The article provides information about an upcoming conference from the program chair. The Microscopy Society of America (MSA), the Microanalysis Society (MAS), and the International Metallographic Society (IMS) invite participation in Microscopy & Microanalysis 2016 in Columbus, Ohio, July 24 through July 28, 2016.

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TYPE Journal Article YEAR 2016
DOIOSTI

General predictive model of friction behavior regimes for metal contacts based on the formation stability and evolution of nanocrystalline surface films

Science

Argibay, Nicolas A.; Cheng, Shengfeng; Sawyer, W.G.; Michael, Joseph R.; Chandross, M.

The prediction of macro-scale friction and wear behavior based on first principles and material properties has remained an elusive but highly desirable target for tribologists and material scientists alike. Stochastic processes (e.g. wear), statistically described parameters (e.g. surface topography) and their evolution tend to defeat attempts to establish practical general correlations between fundamental nanoscale processes and macro-scale behaviors. We present a model based on microstructural stability and evolution for the prediction of metal friction regimes, founded on recently established microstructural deformation mechanisms of nanocrystalline metals, that relies exclusively on material properties and contact stress models. We show through complementary experimental and simulation results that this model overcomes longstanding practical challenges and successfully makes accurate and consistent predictions of friction transitions for a wide range of contact conditions. This framework not only challenges the assumptions of conventional causal relationships between hardness and friction, and between friction and wear, but also suggests a pathway for the design of higher performance metal alloys.

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TYPE Journal Article YEAR 2015
OSTIOSTI

Elevated temperature tribology of cobalt and tantalum-based alloys

Wear

Scharf, Thomas W.; Prasad, Somuri V.; Kotula, Paul G.; Michael, Joseph R.; Robino, Charles V.

This paper describes the friction and wear behavior of a Co–Cr alloy sliding on a Ta–W alloy. Measurements were performed in a pin-on-flat configuration with a hemispherically tipped Co-base alloy pin sliding on a Ta–W alloy flat from ambient to 430 °C. Focused ion beam-scanning electron microscopy (FIB-SEM) and cross-sectional transmission electron microscopy (TEM) were used to identify the friction-induced changes to the chemistry and crystal structure in the subsurface regions of wear tracks. During sliding contact, transfer of material varied as a function of the test temperature, either from pin-to-flat, flat-to-pin, or both, resulting in either wear loss and/or volume gain. Friction coefficients (μ) and wear rates also varied as a function of test temperature. The lowest friction coefficient (μ=0.25) and wear rate (1×10−4 mm3/N m) were observed at 430 °C in argon atmosphere. This was attributed to the formation of a Co-base metal oxide layer (glaze), predominantly (Co, Cr)O with Rocksalt crystal structure, on the pin surface. Part of this oxide film transferred to the wear track on Ta–W, providing a self-mated oxide-on-oxide contact. Once the oxide glaze is formed, it is able to provide friction reduction for the entire temperature range of this study, ambient to 430 °C. The results of this study indicate that glazing the surfaces of Haynes alloys with continuous layers of cobalt chrome oxide prior to wear could protect the cladded surfaces from damage.

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TYPE Journal Article YEAR 2015
DOIOSTIScopus
Results 76–100 of 261
Results 76–100 of 261