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) and differential scanning calorimeter (DSC) were used to examine surface morphology and microstructure of the coating. Aqueous corrosion was done in 3%NaCl+5%H2SO4 solution and high temperature oxidation was done at 750 ℃ in air. 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. At high temperature, Ni3P precipitation and Ni crystallization took place in both coatings at different temperatures. Aqueous corrosion property and high temperature oxidation property of the composite coating were remarkably improved due to the coating's microstructure change and the rare earth doping effect. During the co-deposition process, some Cen+(n=3, 4) ions may be adsorbed to metal/solution interface and hinder nickel deposition. Ni-P/CeO2 coating's perfect amorphous structure results from the hindered crystal-typed deposition of nickel and the promoted deposition of phosphorous.
Isothermal oxidation behavior of chromium with and without nanon sol-gel CeO2 coating is studied at 1 000 ℃ in air.Scanning electron microscopy(SEM) and transmission electron microscopy(TEM) are used to examine the surface morphology and microstructure of the oxide films.It is found that ceria coating greatly improves the anti-oxidation property of chromium.Laser Raman spectrometer and X-ray diffraction spectrometer(XRD) are also used to study the stress level in oxide films formed on ceria-coated and ceria-free Cr.Secondary ion mass spectrometer(SIMS) is used to examine Cr,O and Ce element distribution in depth in oxide films.Results show that nano-ceria application greatly reduces the growth speed and grain size of Cr2O3 film,and this fine grained Cr2O3 film probably has better high temperature plasticity,i.e.,oxide film relieves part of the compressive stress by means of creeping.Meanwhile,CeO2 changes the oxide film growth mechanism from predominant cation outward diffusion to anion inward diffusion.XRD and Raman testing results both show the stress declination effect due to nano-CeO2 application,and their discrepancy in the rare earth effect is analyzed.
The isothermal and cyclic oxidizing kinetics of Co-40Cr alloy and its yttrium ion-implanted samples were studied at 1000℃in air by thermal-gravity analysis(TGA).Scanning electronic microscopy(SEM) was used to examine the Cr 2 O 3 oxide film’s morphology after oxidation.Secondary ion mass spectroscopy(SIMS) method was used to examine the binding energy change of chromium caused by yttrium doping.Acoustic emission(AE)method was used in situ to monitor the cracking and spalling of oxide films formed on both samples during oxidizing and subsequent air-cooling stages.It is found that yttrium implantation remarkably reduces the isothermal oxidizing rate of Co-40Cr and improves the anti-cracking and anti-spalling properties of Cr 2 O 3 oxide film.The reasons for the improvements are mainly that implanted yttrium reduces the grain size of Cr 2 O 3 oxide,increases the high temperature plasticity of oxide film,and remarkably reduces the number and size of Cr 2 O 3 /Co-40Cr interfacial defects.
Isothermal oxidation behavior of chromium with and without nanometric sol-gel CeO_2 coating is studied at 1000℃in air. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are used to examine the surface morphology and microstructure of their oxide films.It is found that ceria coating greatly improves the anti-oxidation property of chromium. Laser Raman spectrometer and X-ray diffraction spectrometer (XRD) are also used to study the stress level in oxide films formed on ceria-coated and ceria-free Cr.The difference in oxidation behavior is mainly attributed to the fact that ceria greatly reduces the growth speed and grain size of Cr_2O_3 film,and this free grain-sized Cr_2O_3 film probably has better high temperature plasticity,i.e. oxide film can relieve parts of compressive stress by means of creeping.XRD and Raman testing results both show the stress declination due to nano-CeO2 application,and their deviation is analyzed concerning to the rare earth effect.
