Indentation size effect in exceptionally hard AlCu thin films

Dual DC magnetron sputtered AlCu thin films representing the whole composition range were investigated by depth-sensing indentation (DSI), transmission electron microscopy (TEM) and atomic force microscopy (AFM). Experimental results show exceptionally high hardness of ∼16 GPa in the middle concentration range of ∼40–70 at% Cu. Indentation tests also revealed phenomena related to indentation size-effect. At Al or Cu contents below 20 at%, the well-known size effect was not observed, which can be interpreted by the grain boundary sliding deformation mechanism of fine-grained films. In the middle range of the composition, the size effect can be clearly observed even against the fine grain structure. This is a consequence of the highly precipitated microstructure of these films, which leads to the indentation processes taking place in a manner more characteristic of amorphous materials.