Electroless Ni-P/nano-CeO2 composite coating was prepared in acidic condition, and its microstructure and corrosive property were compared with its CeO2-free counterpart.Scanning electronic microscopy（SEM）, transmission electronic microscopy（TEM）, X-ray diffraction spectrometer（XRD）, and differential scanning calorimeter（DSC） were used to examine surface morphology and microstructure of the coating.Corrosive investigation was carried out in 3%NaCl＋5%H2SO4 solution.The results showed that Ni-P coating had partial amorphous structure mixed with nanocrystals, whereas the Ni-P/CeO2 coating had perfect amorphous structure.In high temperature condition, Ni3P precipitation and Ni crystallization occurred in both coatings but at different temperatures, whereas the Ni-P/CeO2 coating had sintered phase of NiCe2O4 spinels.The anticorrosion property and passivity were improved in the CeO2-containing coating due to its less liability to undergo local-cell corrosion than its CeO2-free counterpart.During the co-deposition process, some Cen＋（n=3, 4） ions may be adsorbed to the metal/solution interface, hinder nickel＇s crystal-typed deposition and promote phosphorous deposition.The nano-CeO2 doping finally resulted in the coating＇ perfect amorphous structure and good anti-corrosive property.
The isothermal and cyclic oxidizing kinetics of Co-40Cr alloy and its lanthanum ion-implanted samples were studied at 1000 ℃ in air by thermal-gravity analysis （TGA）. Scanning electronic microscopy （SEM） and transmission electronic microscopy （TEM）） were used to examine the oxidized film＇s morphology and the structure after oxidation. Secondary ion mass spectrum （SIMS） method was used to examine the binding energy change of chromium caused by La-doping and its influence on formation of Cr2O3 film. Laser Raman spectrum was used to examine the tress changes within oxidized films. It was found that lanthanum implantation remarkably reduced the isothermal oxidizing rate of Co-40Cr and improved the anti-cracking and anti-spalling properties of Cr2O3 film. The reasons were that the implanted lanthanum reduced the grain size and internal stress of Cr2O3 oxide, increased the high temperature plasticity of oxidized film. Lanthanum mainly existed in the outer surface of Cr2O3 film in the forms of fine La2O3 and LaCrO3 spinel panicles.
Electroless Ni-P/nano-CeO2 composite coating was prepared in acidic condition, and its microstructure and corrosive property were compared with its CeO2-free counterpart. Scanning electronic microscopy （SEM） and X-ray diffraction （XRD） spectrometer were used to examine surface morphology and structure of the as-plated coating. Differential scanning calorimeter （DSC） and transmission electronic microscopy （TEM） were used to study the coating＇s phase change at high temperature. The coating＇s corrosive behavior in 3%NaCl ＋ 5%H2SO4 solution was also investigated. The results showed that Ni-P coating had partial amorphous structure mixed with nano-crystals, while the Ni-P/CeO2 coating had perfect amorphous structure. In high-temperature condition, Ni3P precipitation and Ni crystallization took place in both coatings but at different temperatures, while the Ni-P/CeO2 coating had sintered phase of NiCe2O4 spinels. The anti-corrosion property was better in the CeO2-containing coating, and this was due to its less liability to undergo local-cell corrosion than its CeO2-free counterpart. Ni-P/CeO2 coating＇s pure amorphous structure was the result of Ni＇s hindered crystal-typed deposition and P＇s promoted deposition.
