Epitaxial growth and superhardness effect of TiN/AlON nanomultilayers synthesized by reactive magnetron sputtering technology

Ti and Al2O3 targets were used to synthesize a series of TiN/AlON nanomultilayers in the gas mixture of Ar and N2 through reactive magnetron sputtering technology. The formation of AlON and the effect of AlON thickness on microstructures and mechanical properties of the multilayers were evaluated by means of energy dispersive spectrometry, X-ray diffractometry, high-resolution field transmission electron microscopy and nanoindentation. The results revealed that AlON was formed when Al2O3 target was sputtered in the gas mixture of Ar and N2 resulting from O atoms in Al2O3 being partially replaced by N atoms. Under normal deposition conditions, AlON was amorphous. However, as a component of nanomultilayers, AlON, when thickness being less than 0.6 nm, was forced to crystallize and grew epitaxially on TiN due to the template effect, and the resultant nanomultilayer yielded superhardness effect with a maximum hardness value of 40.5 GPa. When AlON's thickness was increased up to 0.6 nm, its growth mode returned from crystalline back to amorphous, and the epitaxial structure was destroyed, resulting in the disappearance of superhardness effect.