Microscopic Evidences of Nanocomposite Structure in Hard and Optically Transparent Ternary AlSiN Coating

In this work AlSiN ternary coatings were deposited by radio frequency magnetron sputtering in Ar/N2 reactive atmosphere. AlSi alloy target of composition 86:14 wt% has been used to deposit the coatings on float glass substrate by varying the Ar:N2 ratio i.e., 20:4, 20:6, 20:8, 20:13 and 20:15. The effect of different Ar:N2 ratio on microstructure, mechanical and optical property were studied using x-ray diffraction (XRD), stylus profilometry, Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray Spectroscopy (EDS), High Resolution Transmission Electron Microscopy (HRTEM), UV–visible spectrometry and manoindentation. The XRD measurements show the formation h-AlN phase for coating deposited for 20:6 only and confirm the crystalline nature of the coating whereas at higher and lower Ar: N2 ratio, the measurements show the amorphous nature of the coatings. 20:6 deposited coating developed a wurtzite-AlN nanocrystalline structure. The thickness of the coatings decreased with respect to the increasing Ar: N2 ratio. The FESEM shows uneven and dense microstructure of the coatings. HRTEM study confirms the amorphous nature of 20:4 and 20:13 Ar: N2 ratio, and the polycrystalline nature of 20:6 coating. The elemental compositions were confirmed by EDS. The optical transparency of the coating was more than 95% for all the coatings in the visible range. The roughness of the samples was also measured in scanning probe microscopy imaging that showed an average roughness value Ra of ∼3 nm. The maximum hardness of 31 GPa was observed for the coating prepared with an Ar: N2 ratio of 20:6.

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MiniLabES060A

Deposition of AlSiN Coatings

The AlSiN coatings were deposited by using RF reactive magnetron sputtering (Minilab ES60A, Moorfield, UK) system, with the help of circular AlSi (86:14 wt%) alloy target of ∼50 mm diameter and 3 mm thickness. 

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