The effect of NiCr intermediate layer on corrosion behavior of Cr2O3 ceramic coated materials

The NiCr plasma-sprayed deposition, as an intermediate layer, is normally u sed to improve the adhesion between the metal substrate and the ceramic coa ting. Defects, such as pores and micro-cracks, generally exist in the ceram ic layer, and lead to corrosion beneath the coating. The present work used plasma-sprayed specimens, such as the Cr2O3 ceramic coatings with and witho ut a NiCr intermediate layer and the single NiCr coatings, etc. which were deposited on a SUS316L stainless steel substrate. The results of corrosion tests and electrochemical experiments indicated that the corrosion resistan ce of the 80NiCr (80Ni-20Cr) coating was weaker than that of the SUS316 sub strate, while that of 50NiCr (50Ni-50Cr) was better than that of the substr ate. The existence of 80NiCr plasma-sprayed intermediate layer decreased th e corrosion resistance of the Cr2O3 ceramic coated specimen, while the 50Ni Cr increased it. The microstructure analysis demonstrated that both the 80N iCr and 50NiCr plasma-sprayed coatings consisted of the matrix and a second -phase structure. Energy dispersive spectroscopy (EDS), wave dispersive spe ctroscopy (WDS) and X-ray diffractometry (XRD) analysis showed that the com ponents of the matrix and the second-phase in 50NiCr were different from th ose in 80NiCr. In addition, this paper preliminarily discusses the corrosio n mechanism of 80NiCr and 50NiCr intermediate layers. The different chromiu m content in the matrix of the 80NiCr and 50NiCr coatings might have caused the difference in the corrosion resistance between them. It can be predict ed that the decrease of porosity by means of plasma spraying or sealing tre atment of the ceramic coating, as well as by regulating the components of t he NiCr intermediate layer, would improve the corrosion resistance of Cr2O3 ceramic coated materials. (C) 2000 Elsevier Science S.A. All rights reserv ed.