The isothermal and cyclic oxidizing kinetics of Co-40Cr alloy and its lanthanum ion-implanted samples were studied at 1 000 ℃ in air by thermal gravimetric analysis（TGA）.Scanning electron microscopy（SEM）was used ...The isothermal and cyclic oxidizing kinetics of Co-40Cr alloy and its lanthanum ion-implanted samples were studied at 1 000 ℃ in air by thermal gravimetric analysis（TGA）.Scanning electron microscopy（SEM）was used to examine the Cr2O3 oxide film＇s morphology 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 the formation of Cr2O3 film.Acoustic emission（AE）method was used in situ to monitor the cracking and spalling of oxide films during oxidizing and subsequent air-cooling stages.Laser Raman spectrum was used to examine the stress changes within oxide films.A theoretical model was proposed relating to the film fracture process and was used to analyze the AE spectrum both on time domain and AE-event number domain.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 oxide film.The reasons for the improvement were mainly that the implanted lanthanum reduced the grain size and internal stress of Cr2O3 oxide,increased the high temperature plasticity of oxide film,and remarkably reduced the number and size of Cr2O3/Co-40Cr interfacial defects.展开更多
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 examin...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.展开更多
基金Item Sponsored by National Natural Science Foundation of China(59231011)
文摘The isothermal and cyclic oxidizing kinetics of Co-40Cr alloy and its lanthanum ion-implanted samples were studied at 1 000 ℃ in air by thermal gravimetric analysis（TGA）.Scanning electron microscopy（SEM）was used to examine the Cr2O3 oxide film＇s morphology 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 the formation of Cr2O3 film.Acoustic emission（AE）method was used in situ to monitor the cracking and spalling of oxide films during oxidizing and subsequent air-cooling stages.Laser Raman spectrum was used to examine the stress changes within oxide films.A theoretical model was proposed relating to the film fracture process and was used to analyze the AE spectrum both on time domain and AE-event number domain.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 oxide film.The reasons for the improvement were mainly that the implanted lanthanum reduced the grain size and internal stress of Cr2O3 oxide,increased the high temperature plasticity of oxide film,and remarkably reduced the number and size of Cr2O3/Co-40Cr interfacial defects.
基金Item Sponsored by National Natural Science Foundation of China(59231011)
文摘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.
