Comparison of the structural and corrosion properties of the graphene/SiN(200) coating system deposited on titanium alloy surfaces covered with SiN transition layers

• SiN transition layer improves structural properties of the graphene/SiN(200) coating system.
• SiN transition layer improves corrosion properties of the graphene/SiN(200) coating system
• icorr for SiN(300)/graphene/SiN(200) coatings system decrease to 1.11 · 10− 10 A/cm2.
• Ecorr for SiN(300)/graphene/SiN(200) coatings system decreases to − 0.41 V.
• The OCP for SiN(300)/graphene/SiN(200) coatings system changed by only about 60 mV during 1 h.

In this paper, comparative studies of the structural and corrosion properties of SiN/graphene/SiN coating systems with various SiN transition layer thickness have been investigated. The coating systems were formed on Ti6Al4V alloy surfaces. The SiN transition layer thicknesses varied from 100 nm to 300 nm. The thickness of the upper silicon nitride thin film, in all examined cases, was 200 nm. The silicon nitride thin film was deposited using the Plasma Enhanced Chemical Vapour Deposition method. A graphene monolayer was transferred onto the silicon nitride surface using the “PMMA-mediated” method.The structural characteristics of coating systems obtained were examined using Raman spectroscopy, optical profilometry and SEM measurements. The corrosion properties of the coating systems were determined by an analysis of the voltammetric curves.The SiN/graphene/SiN coating system with a 300 nm thick silicon nitride transition layer is characterised by the best structural and corrosion properties of all tested coating systems. In this case, the surface of the top silicon nitride thin film has no holes or flakes, as opposed to the coating systems with 100 nm and 200 nm thick transition layers, in which the upper SiN thin film flaked and dropped off. The value of corrosion current density obtained for this sample was almost two orders of magnitude lower than the current density obtained for the other tested coating systems.