Subsurface microstructure evolution and deformation mechanism of Ag-Cu eutectic alloy after dry sliding wear

Dry sliding wear behavior of nanostructured eutectic Ag-Cu with grain size ~114 nm was investigated using pin-on-disc testing. The subsurface microstructure and texture evolution were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nano-beam diffraction, and high angle annular dark field. During sliding wear, plastic deformation transforms the subsurface material into hierarchical microstructures. At depths of 1-15 μm below the sliding surface, a two phase (Ag-rich and Cu-rich) nano-lamellar structure is observed, where the layer thickness decreases from 98 nm at a depth of 15 μm to 11 nm at a depth of 1 μm. Right below the sliding surface, where an equivalent strain of 7.1 was estimated, wear induced plastic deformation drives the subsurface material into a non-equilibrium super-saturated solid solution phase, with ~9 nm equiaxed nano-grains. These refined microstructures led to significant work-hardening in the subsurface material, as revealed by nanoindentation testing. Finally, the microstructure evolution and the underlying deformation mechanism of Ag-Cu are discussed on the basis of these characterizations.