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Shear-induced softening of nanocrystalline metal interfaces at cryogenic temperatures

Scripta Materialia

Argibay, Nicolas; Curry, John F.; Babuska, Tomas F.; Lu, Ping; Chandross, Michael E.; Furnish, Timothy A.; Kustas, Andrew B.

We demonstrate inverse Hall-Petch behavior (softening) in pure copper sliding contacts at cryogenic temperatures. By kinetically limiting grain growth, it is possible to generate a quasi-stable ultra-nanocrystalline surface layer with reduced strength. In situ electrical contact resistance measurements were used to determine grain size evolution at the interface, in agreement with reports of softening in highly nanotwinned copper. We also show evidence of a direct correlation between surface grain size and friction coefficient, validating a model linking friction in pure metals and the transition from dislocation mediated plasticity to grain boundary sliding.

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TYPE Journal Article YEAR 2018
DOIOSTIScopus

Linking microstructural evolution and macro-scale friction behavior in metals

Journal of Materials Science

Argibay, Nicolas; Chandross, Michael E.; Cheng, S.; Michael, Joseph R.

A correlation is established between the macro-scale friction regimes of metals and a transition between two dominant atomistic mechanisms of deformation. Metals tend to exhibit bi-stable friction behavior—low and converging or high and diverging. These general trends in behavior are shown to be largely explained using a simplified model based on grain size evolution, as a function of contact stress and temperature, and are demonstrated for self-mated pure copper and gold sliding contacts. Specifically, the low-friction regime (where µ < 0.5) is linked to the formation of ultra-nanocrystalline surface films (10–20 nm), driving toward shear accommodation by grain boundary sliding. Above a critical combination of stress and temperature—demonstrated to be a material property—shear accommodation transitions to dislocation dominated plasticity and high friction, with µ > 0.5. We utilize a combination of experimental and computational methods to develop and validate the proposed structure–property relationship. This quantitative framework provides a shift from phenomenological to mechanistic and predictive fundamental understanding of friction for crystalline materials, including engineering alloys.

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TYPE Journal Article YEAR 2017
DOIOSTIScopus

Stress-dependent grain size evolution of nanocrystalline Ni-W and its impact on friction behavior

Scripta Materialia

Argibay, Nicolas; Furnish, Timothy A.; Boyce, Brad L.; Clark, Blythe C.; Chandross, Michael E.

The friction behavior of ultra-nanocrystalline Ni-W coatings was investigated. A critical stress threshold was identified below which friction remained low, and above which a time-dependent evolution toward higher friction behavior occurred. Founded on established plasticity models we propose a correlation between surface grain size and applied stress that can be used to predict the critical stress separating the two friction regimes. This interpretation of plasticity models suggests that macro-scale low and high friction regimes are respectively associated with the nano-scale mechanisms of grain boundary and dislocation-mediated plasticity.

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TYPE Journal Article YEAR 2016
DOIOSTIScopus
Results 101–125 of 192
Results 101–125 of 192
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