Comprehensive characterisation of the Al-Cu binary thin film system: Correlation between composition, microstructure and mechanical properties

In this study, a thorough mechanical and structural characterization of the entire Al-Cu binary thin film system has been carried out. Our novel combinatorial approach to facilitate complex studies of the entire layer system ensured both an efficient fabrication and characterisation. Using dual DC magnetron sputtering, fifteen Al 100-x Cu x layers of varying compositions (0≤x≤100) were deposited in adjacent strips on a single, native oxide covered Si substrate. Microstructure and mechanical properties of the layers were comprehensively investigated by transmission electron microscopy (TEM) and nanoindentation. Experimental results show that at the near equiatomic compositions, the microstructure of the layers is a mixture of different hard, non-equilibrium phase ( Θ -Al 2 Cu, γ -Al 4 Cu 9 ) components, resulting in exceptional strength with a maximum hardness up to ~16 GPa. Due to the hard matrix, the layers in the range of 40-70 at.% Cu can be characterized by brittle deformation, strong indentation size effect (ISE) and plastic instability. In contrast, Al layers with low Cu content or Cu layers with low Al content deform plastically, mainly by grain boundary sliding, and as a result, no ISE occurs in these layers. Based on the revealed mechanical behaviour and microstructural properties, deformation mechanisms operating at different stages of the whole compositional range have been proposed. • A thorough mechanical and structural characterization of the entire Al-Cu binary thin film system. • Non-equilibrium, hard phase ( Θ -Al 2 Cu, γ -Al 4 Cu 9 ) components, resulting in exceptional strength. • Hard matrix characterized by brittle deformation, strong indentation size effect (ISE) and plastic instability. • Deformation mechanisms operating at different stages of the whole compositional range have been proposed.