Study on the superhardness mechanism of $Ti–Si–N$ nanocomposite films: Influence of the thickness of the $Si3N4$ interfacial phase

The superhardness effect of $Ti–Si–N$ nanocomposite films is closely related to the thickness of the interfacial phase, $Si3N4$⁠. The influence of the thickness of $Si3N4$ on the growth structure and mechanical properties of $Ti–Si–N$ nanocomposite films was determined by studying $TiN∕Si3N4$ multilayers with different thicknesses of $Si3N4$ layers to reveal the strengthening mechanism of the nanocomposite films. The results show that $Si3N4$⁠, which is amorphous in single film, can exist as a crystalline structure in $TiN∕Si3N4$ multilayers when the thickness of the $Si3N4$ layers is less than $0.7nm$ because of the “template effect” of $TiN$⁠. As a result, $TiN$ and $Si3N4$ layers form a coherent epitaxial growth with a preferred orientation. As a result, the multilayers exhibit a superhardness effect. When the thickness is greater than $0.7nm$⁠, $Si3N4$ exists as an amorphous structure and prevents $TiN$ from coherent epitaxial growth with it, resulting in the decrease of the hardness and elastic moduli of the multilayers. The experiments reveal that when the thickness is less than $0.7nm$⁠, the $Si3N4$ interfacial phase in $Ti–Si–N$ nanocomposite films may have the same structure as that in $TiN∕Si3N4$ multilayers. The strengthening mechanism of $Ti–Si–N$ nanocomposite films may be the same as that of $TiN∕Si3N4$ nanomultilayers formed by the coherent epitaxial growth of two layers with different moduli.