Journal
JOURNAL OF MATERIALS SCIENCE
Volume 52, Issue 5, Pages 2780-2799Publisher
SPRINGER
DOI: 10.1007/s10853-016-0569-1
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Funding
- Laboratory Directed Research and Development program at Sandia National Laboratories
- U.S. Department of Energy's National Nuclear Security Administration [DE-AC04-94AL85000]
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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 A mu < 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 A mu > 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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