Scratching an Al/Si Interface: Molecular Dynamics Study of a Composite Material
ZB Zhang and IA Alhafez and HM Urbassek, TRIBOLOGY LETTERS, 66, 86 (2018).
We study scratching of a composite built from two widely different materials, a ductile and soft metal (Al) and a hard and brittle ceramic (Si). When scratching far away from the interface, the response of the pure elemental materials is monitored. A higher hardness and a lower friction coefficient are found for Si as compared to Al. The pile-up in Al is larger than in Si. When scratching along the interface, the composite responds approximately with the averaged behavior of the two pure materials. This applies to the forces as well as to the hardness and the friction coefficient. However, we observe a peculiar material flow, which can be described by a rotation around the scratch direction, inducing material mixing both in the groove bottom and in the pile-up; the harder Si expands on the groove bottom, while the softer Al expands in the pile-up region. When scratching across the interface, the material response switches on a length scale of the order of the contact radius. While the friction coefficient and the contact pressure switch from and to the values of the respective pure material, the behavior of the forces and areas is more complex. This is in particular due to the lateral pile-up that forms differently on the ductile metal and the amorphized Si parts.
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