Microstructure and mechanical properties of CrAlN/SiNx nanostructure multilayered coatings

Multilayered CrAlN and SiNx films were deposited periodically by radio frequency reactive magnetron sputtering. In the CrAlN/SiNx multilayered coatings, the thickness of CrAlN layer was fixed at 4 nm, while that of SiNx layer was adjusted from 4 nm to 0.3 nm. The dependence of the SiNx layer thickness on the preferred orientation, crystalline behavior and mechanical properties of multilayered coatings were discussed with the aid of XRD patterns and HRTEM. It was demonstrated that amorphous SiNx layer transformed to a crystallized one when the thickness decreased from 4 nm to 0.3 nm. The crystalline SiNx layer grew epitaxially, formed the coherent interface with the CrAlN layer, and the columnar structure was exhibited. The critical layer thickness for the transition from amorphous SiNx to a crystallized one was found to be around 0.4 nm, and maximum hardness of 33 GPa was revealed.