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.

Automated summary

This study investigated AlCu thin films representing the whole composition range using multiple experimental methods. It was found that the films exhibited exceptionally high hardness in the middle concentration range of 40-70 at% Cu. Furthermore, the grain boundary sliding deformation mechanism and highly precipitated microstructure of the films also influenced the indentation size effect.