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Linking microstructural evolution and macro-scale friction behavior in metals

Journal of Materials Science

Argibay, Nicolas A.; Chandross, M.; 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
ScopusOSTIDOI

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

Scripta Materialia

Argibay, Nicolas A.; Furnish, Timothy A.; Boyce, B.L.; Clark, Blythe C.; Chandross, M.

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
ScopusOSTIDOI

Temperature-Dependent Friction and Wear Behavior of PTFE and MoS2

Tribology Letters

Babuska, Tomas F.; Pitenis, A.A.; Jones, M.R.; Nation, Brendan L.; Sawyer, W.G.; Argibay, Nicolas A.

An investigation of the temperature-dependent friction behavior of PTFE, MoS2, and PTFE-on-MoS2 is presented. Friction behavior was measured while continuously varying contact temperature in the range −150 to 175 °C while sliding in dry nitrogen, as well as for self-mated PTFE immersed in liquid nitrogen. These results contrast with previous reports of high-friction transitions and plateaus for pure and composite MoS2 at temperatures below about −20 °C; instead, we have found persistently weak thermal behavior between 0 and −196 °C, providing new insight about the molecular mechanisms of macroscale friction. The temperature-dependent friction behavior characteristic of self-mated PTFE was found also for PTFE-on-MoS2 sliding contacts, suggesting that PTFE friction was defined by subsurface deformation mechanisms and internal friction even when sliding against a lamellar lubricant with extremely low friction coefficient (µ ~ 0.02). The various relaxation temperatures of PTFE were found in the temperature-dependent friction behavior, showing excellent agreement with reported values acquired using rheological techniques measuring energy dissipation through internal friction. Additionally, hysteresis in friction behavior suggests an increase in near-surface crystallinity upon exceeding the high-temperature relaxation, Tα ~ 116 °C.

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TYPE Journal Article YEAR 2016
ScopusOSTIDOI
Results 76–100 of 139
Results 76–100 of 139