Microstructure and corrosion resistance of Ni-based alloy laser coatings with nanosize CeO2 addition

摘要

Micron-size Ni-base alloy (NBA) powders were mixed with both 1.5?wt.% (hereinafter %) micron-size CeO₂ ( m - CeO₂ ) and also 1.5% and 3.0% nano-size CeO₂ ( n - CeO₂ ) powders. These mixtures were coated on low-carbon steel (Q235) by 2.0?kW CO₂ laser cladding. The effects on the microstructures, phases and electrochemical corrosion of the coatings upon the addition of m- and n - CeO₂ powders to NBA (m- and n - CeO₂ /NBA ) have been investigated. The results showed that a smooth coating was prepared under suitable processing parameters ( P= 2.0?kW , V= 180?mm?min^{- 1} ) by adding 1.5% n - CeO₂ . In addition to the primary phases of γ - Ni , Cr₂₃ C₆ and Ni₃ B in the Ni-base alloy coating, CeNi₃ was formed in Ni-base alloy coatings with both n - CeO₂ and m - CeO₂ particles, and CeNi₅ appeared in the coating upon decreasing the size of CeO₂ particles. Well-developed dendrites were observed in the Ni-base alloy coating; directional dendrites grew at the interface in the coating upon the addition of m - CeO₂ , whereas fine and multioriented dendrites grew upon decreasing the size of CeO₂ particles to the nanoscale. Actinomorphic dendrites and compact equiaxed dendrites grew from the interface to near the surface upon increasing the content of n - CeO₂ from 1.5 to 3.0%. In strongly acidic HNO₃ solution, the severe corrosion of dendrites occurred and there were many corrosion pits in the Ni-base alloy coating; intercrystalline corrosion also has a dominant role upon the addition of m - CeO₂ , whereas uniform corrosion occurs in the coating as the size of CeO₂ particles is decreased to nanoscale.