Microstructure and mechanical properties of VAlN/Si₃N₄ nano-multilayer coatings

Abstract

VAlN coating is of particular interest for dry cutting applications owing to its low-friction and excellent abrasiveness. Nano-multilayer structure is designed to tailor the properties of VAlN coating. In this work, a series of VAlN/Si₃N₄ nano-multilayer coatings with varied Si₃N₄ layer thicknesses were prepared by reactive sputtering method. The microstructure and mechanical properties of the coatings were both investigated. It is revealed that Si₃N₄ with a shallow thickness (∼0.4 nm) was crystallized and grown coherently with VAlN, showing a remarkable increase in hardness compared to VAlN monolayer coating. The hardness of coherently VAlN/Si₃N₄ nano-multilayer coatings reached to 48.7 GPa. With further increase of Si₃N₄ layer thickness, the coherent growth of nano-multilayers was terminated, showing amorphous structure formed in nano-multilayers and the hardness was declined. On the other hand, when Si₃N₄ layer thickness was 0.4 nm, the friction coefficient of VAlN/Si₃N₄ nano-multilayer coating was almost equal to that of VAlN monolayer coating, which was attributed to the crystallization of Si₃N₄ and the produced coherent interfaces between VAlN and Si₃N₄ for the hardening effect of nano-multilayer coatings. Upon further increase of Si₃N₄ layer thickness, pronounced improvement of friction coefficient in VAlN/Si₃N₄ nano-multilayer coating was observed.

Keywords

VAlN/Si₃N₄ / nano-multilayer coatings / mechanical properties / microstructure / superhardness effect

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