Isothermal and cyclic oxidation behaviors of pure and yttrium-implanted nickel were studied at 1000 ℃ in the air. Scanning electronic microscopy (SEM) and transmission electronic microscopy (TEM) were used to examine...Isothermal and cyclic oxidation behaviors of pure and yttrium-implanted nickel were studied at 1000 ℃ in the air. Scanning electronic microscopy (SEM) and transmission electronic microscopy (TEM) were used to examine the micro-morphology and structure of oxide scales formed on nickel substrate. It was found that Y-implantation greatly improved the anti-oxidation ability of nickel both in isothermal and cyclic oxidizing experiments. Laser Raman Microscopy was also used to study the stress status of oxide scales formed on nickel with and without yttrium. The main reason for the improvement in anti-oxidation of nickel was that Y-implantation greatly reduced the growing speed and grain size of NiO. This fine-grained NiO oxide film might have better high temperature plasticity and could relieve parts of compressive stress by means of creeping, and maintained ridge character and relatively lower internal stress level, hence remarkably enhanced the adhesion of protective NiO oxide scale formed on nickel substrate. The actual existing form of yttrium in oxide can be Y2O3 and NiY2O4 spinel nanometric particles, and even be Y3+ ions segregated at NiO grain boundaries.展开更多
The isothermal oxidizing kinetics of Co-40Cr alloy and its yttrium ion-implanted samples are studied at 1 000 ℃ in air by thermal-gravity analysis （TGA）. Scanning electronic microscopy （SEM） is used to examine th...The isothermal oxidizing kinetics of Co-40Cr alloy and its yttrium ion-implanted samples are studied at 1 000 ℃ in air by thermal-gravity analysis （TGA）. Scanning electronic microscopy （SEM） is used to examine the Cr2O3 oxide film＇s morphology after oxidation. Acoustic emission （AE） method is used in situ for monitoring the cracking and spalling of oxide films formed on both samples during oxidizing and subsequent air-cooling stages. Theoretical model is proposed relating to the film fracture process and is used for analyzing the acoustic emission spectrum both on time domain and on AE-event number domain. 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 Cr2O3 oxide film. The reasons for the improvement are mainly that the implanted yttrium reduced the grain size of Cr2O3 oxide, increased the high temperature plasticity of oxide film, and remarkably reduced the number and size of Cr2O3/Co-40Cr inteffacial defects.展开更多
基金the National Natural Science Foundation of China (29231011)the National Natural Science Foundation of Colombia (M018327)
文摘Isothermal and cyclic oxidation behaviors of pure and yttrium-implanted nickel were studied at 1000 ℃ in the air. Scanning electronic microscopy (SEM) and transmission electronic microscopy (TEM) were used to examine the micro-morphology and structure of oxide scales formed on nickel substrate. It was found that Y-implantation greatly improved the anti-oxidation ability of nickel both in isothermal and cyclic oxidizing experiments. Laser Raman Microscopy was also used to study the stress status of oxide scales formed on nickel with and without yttrium. The main reason for the improvement in anti-oxidation of nickel was that Y-implantation greatly reduced the growing speed and grain size of NiO. This fine-grained NiO oxide film might have better high temperature plasticity and could relieve parts of compressive stress by means of creeping, and maintained ridge character and relatively lower internal stress level, hence remarkably enhanced the adhesion of protective NiO oxide scale formed on nickel substrate. The actual existing form of yttrium in oxide can be Y2O3 and NiY2O4 spinel nanometric particles, and even be Y3+ ions segregated at NiO grain boundaries.
基金National Natural Science Foundation of China(No.29231011)Natural Science Foundation of Jiangsu Province,China(No.07KJD430246)
文摘The isothermal oxidizing kinetics of Co-40Cr alloy and its yttrium ion-implanted samples are studied at 1 000 ℃ in air by thermal-gravity analysis （TGA）. Scanning electronic microscopy （SEM） is used to examine the Cr2O3 oxide film＇s morphology after oxidation. Acoustic emission （AE） method is used in situ for monitoring the cracking and spalling of oxide films formed on both samples during oxidizing and subsequent air-cooling stages. Theoretical model is proposed relating to the film fracture process and is used for analyzing the acoustic emission spectrum both on time domain and on AE-event number domain. 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 Cr2O3 oxide film. The reasons for the improvement are mainly that the implanted yttrium reduced the grain size of Cr2O3 oxide, increased the high temperature plasticity of oxide film, and remarkably reduced the number and size of Cr2O3/Co-40Cr inteffacial defects.
