Microscopic evidences of nanocomposite structure in hard and optically transparent ternary AlSiN coating

Abstract

In this work AlSiN ternary coatings were deposited by radio frequency magnetron sputtering in Ar/N-2 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:N-2 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 crys-talline nature of the coating whereas at higher and lower Ar: N-2 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: N-2 ratio. The FESEM shows uneven and dense microstructure of the coatings. HRTEM study confirms the amorphous nature of 20:4 and 20:13 Ar: N-2 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 similar to 3 nm. The maximum hardness of 31 GPa was observed for the coating prepared with an Ar: N2 ratio of 20:6.