Nanoscale metallic multilayers represent a new class of engineering materials with superior physical, mechanical, and tribological properties. Previous investigations have illustrated that deformation and strength of multilayers depend on the layer thickness and the type of interface between the layers, which directly controls the barrier strength of the interface and the stability of the multilayer structure under mechanical loads. In particular, this structural stability is critical to the performance of multilayer materials under sliding wear since deformation-induced microstructural changes may affect the subsequent wear response of metals under repeated sliding contact.
In this study, Cu/Au and Cu/Cr multilayers with different bilayer thicknesses ranging from 50 – 200 nm were investigated. Sliding experiments at different normal loads with up to 1000 cycles were conducted using a nanoindenter equipped with a spherical tip. The microstructures underneath the sliding tracks were investigated by scanning and transmission electron microscopy. The thinner layers exhibit improved wear behavior. Deformation-induced grain growth, layer thinning and microstructural vortices are observed with increasing number of passes for the Cu/Au system. Waviness of the interfaces appears to be a precondition for the vortex formation. Finally, a mechanically mixed nanocrystalline deformation zone develops beneath the wear tracks. In contrast, the deformation zone of the Cu/Cr system consists of Cr-nanograins in a Cu matrix. The effect of the film thickness and type of interface on the deformation and wear behavior will be discussed.