Improved Corrosion Resistance of Plasma-Sprayed NiCr-Mo Coating with Shell-Core-Structured Powder by Improving Lamellar Interface Bonding

The existence of inter-connected pores in plasma-sprayed alloy coatings dominates their corrosion behavior in a corrosive environment. How to eliminate the connected pores by increasing the lamellae interface bonding in metallic coatings is a great challenge. In this study, a shell-core-structured powder particle design by cladding spherical NiCr powders with refractory molybdenum as alloying element is proposed to limit the evaporation of alloy elements and subsequently raise particle temperature significantly. Results showed that a dense coating with much less porosity was obtained due to the improved lamellar interface bonding by gas shrouded plasma spraying of the composite NiCr/Mo particles compared with NiCr powders. Electrochemical method was employed to measure the anodic polarization behavior of the NiCr/Mo coating to evaluate its connected porosity. The effect of inter-lamellar bonding on the connected porosity and subsequently coating corrosion resistance are discussed based on the theoretical analysis and experimental results.