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Solids under extreme shear: Friction-mediated subsurface structural transformations

: Greiner, C.; Gagel, J.; Gumbsch, P.

Fulltext ()

Advanced Materials 31 (2019), No.26, Art. 1806705, 19 pp.
ISSN: 0935-9648
ISSN: 1521-4095
Deutsche Forschungsgemeinschaft DFG
GR 4174/1
Deutsche Forschungsgemeinschaft DFG
GU 367/30
European Commission EC
H2020; 771237; TriboKey
Deformation Mechanisms are the Key to Understanding and Tayloring Tribological Behaviour
Journal Article, Electronic Publication
Fraunhofer IWM ()
copper; discrete dislocation dynamic; electron microscopy; microstructure; tribology

Tribological contacts consume a significant amount of the world's primary energy due to friction and wear in different products from nanoelectromechanical systems to bearings, gears, and engines. The energy is largely dissipated in the material underneath the two surfaces sliding against each other. This subsurface material is thereby exposed to extreme amounts of shear deformation and often forms layered subsurface microstructures with reduced grain size. Herein, the elementary mechanisms for the formation of subsurface microstructures are elucidated by systematic model experiments and discrete dislocation dynamics simulations in dry frictional contacts. The simulations show how pre-existing dislocations transform into prismatic dislocation structures under tribological loading. The stress field under a moving spherical contact and the crystallographic orientation are crucial for the formation of these prismatic structures. Experimentally, a localized dislocation structure at a depth of ≈100150 nm is found already after the first loading pass. This dislocation structure is shown to be connected to the inhomogeneous stress field under the moving contact. The subsequent microstructural transformations and the mechanical properties of the surface layer are determined by this structure. These results hold promise at guiding material selection and alloy development for tribological loading, yielding materials tailored for specific tribological scenarios.