Influence of vacuum annealing on structures and properties of AlTiSiN coatings with corrosion resistance

The corrosion behaviors in 10 wt% H2SO4 solution of the AlTiSiN coatings, deposited on 316L stainless steel using multi-arc ion plating then vacuum annealed at 700 °C, 800 °C and 900 °C for 2 h, was investigated. The microstructures, compositions and surface morphologies of the coatings were characterized by utilizing X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscope (XPS) and scanning electron microscope (SEM) analyses. The adhesion strength and corrosion behavior of coatings were measured by scratch test and electrochemical polarization curves, respectively. The results indicated that the as-deposited coatings were mainly comprised of solid solution (Ti,Al)N phase and amorphous Si3N4 phase. With increasing annealing temperature, the solid solution gradually decomposed into fcc-TiN and fcc-AlN phases and further into hcp-AlN phase. The defects on coating surface and adhesion strength of coatings were improved simultaneously. The electrochemical results revealed that all coated samples had better corrosion resistance than the substrate, and the coatings annealed at 800 °C exhibited the best corrosion behavior in acid solutions. This was caused by the formation of amorphous Si3N4 phase and anti-corrosion hcp-AlN phase.