Crystal growth and superhardness effects of ZrN/AlON nanomultilayers synthesized by reactive magnetron sputtering

Abstract

Two series of ZrN/AlON nanomultilayers were synthesized by reactively sputtering zirconium and aluminum oxide targets in the gaseous mixture of argon and nitrogen. The thickness of ZrN layers was fixed in one of the series and the thickness of AlON layers in the other. The composition, microstructure and mechanical properties of films were characterized by X-ray energy dispersive spectroscopy, X-ray diffraction, high resolution transmission electron microscopy and nanoindentation. The investigation results indicate that during the process of Al2O3 target sputtering in the mixed atmosphere, part of oxygen atoms in Al2O3 were replaced by nitrogen atoms, leading to the formation of aluminum oxynitride, AlON. Under the influence of the “template effects” of ZrN layers, the AlON layers that used to exist as amorphous under sputtering conditions were forced to crystallize and grew epitaxially with the ZrN layers when the thickness of AlON was limited to less than 0.9 nm. Correspondingly, the hardness of multilayers was remarkably enhanced to its maximum value of 33.0GPa. A further increase in the thickness of AlON layers led to the crystalline AlON layers transforming into amorphous. The epitaxial growth of multilayers was blocked, accompanied by the decline of hardness.