Oxidation behaviors of blank and CeO2 coated T91 steel were investigated at 600 ℃ in water vapor for up to 150 h. Gold marker was used to define the mass transport direction. The oxide scales were studied with X-ray ...Oxidation behaviors of blank and CeO2 coated T91 steel were investigated at 600 ℃ in water vapor for up to 150 h. Gold marker was used to define the mass transport direction. The oxide scales were studied with X-ray diffractometry （XRD）, scanning electron microscopy （SEM） and electron probe microanalyzer （EPMA）. The oxidation resistance of the steel is improved by CeO2 coating, though the improvement is not remarkable. Ce-rich oxide band is located at the interface of the inner equiaxed layer and the outer columnar layer after oxidation, which is not consistent with the original surface. The results show that outward iron transport is blocked by the Ce-rich band. A new oxide nucleating and growing site （reaction front） is induced at the inner surface of the Ce rich band.展开更多
MoSi2 powders were fabricated respectively by mechanical alloying technique and sintering at different temperatures to prepare materials with different relative densities. The relative oxidation behavior of all MoSi2 ...MoSi2 powders were fabricated respectively by mechanical alloying technique and sintering at different temperatures to prepare materials with different relative densities. The relative oxidation behavior of all MoSi2 materials at 1 473 K was investigated by TGA,SEM and XRD. The results show that the "pesting" is not found in all materials after being oxidized for 480 h. The density has no essential relation to the "pesting". The oxidation curve of specimens with lower density shows two-step oxidation kinetics. Both the first stage (0-1 h) and the second stage (1-480 h) nearly obey linear kinetics,but the oxidation rates are obviously different. The oxidation kinetics of MoSi2 with higher relative density nearly follows parabolic law. The mass gains of MoSi2 with the lowest relative density (78.6%) and the highest relative density (94.8%) are increased by 10.390 and 0.135 mg/cm2,respectively. The oxide scale of materials with lower densities is non-protective and makes the oxygen diffusion easy. A dense scale in the material with higher density is formed,which acts as a diffusion barrier to the oxygen atoms to penetrate into the matrix,showing much better high temperature oxidation resistance. The phases distribution of oxidation scale from the outside to the inside is SiO2→Mo5Si3→MoSi2.展开更多
基金Project(2007A-47) supported by Shandong Electric Power Corporation,China
文摘Oxidation behaviors of blank and CeO2 coated T91 steel were investigated at 600 ℃ in water vapor for up to 150 h. Gold marker was used to define the mass transport direction. The oxide scales were studied with X-ray diffractometry （XRD）, scanning electron microscopy （SEM） and electron probe microanalyzer （EPMA）. The oxidation resistance of the steel is improved by CeO2 coating, though the improvement is not remarkable. Ce-rich oxide band is located at the interface of the inner equiaxed layer and the outer columnar layer after oxidation, which is not consistent with the original surface. The results show that outward iron transport is blocked by the Ce-rich band. A new oxide nucleating and growing site （reaction front） is induced at the inner surface of the Ce rich band.
基金Project(50405041) supported by the National Natural Science Foundation of ChinaProject(06C316) supported by the Scientific Research Fund of Hunan Provincial Education Deparment, China
文摘MoSi2 powders were fabricated respectively by mechanical alloying technique and sintering at different temperatures to prepare materials with different relative densities. The relative oxidation behavior of all MoSi2 materials at 1 473 K was investigated by TGA,SEM and XRD. The results show that the "pesting" is not found in all materials after being oxidized for 480 h. The density has no essential relation to the "pesting". The oxidation curve of specimens with lower density shows two-step oxidation kinetics. Both the first stage (0-1 h) and the second stage (1-480 h) nearly obey linear kinetics,but the oxidation rates are obviously different. The oxidation kinetics of MoSi2 with higher relative density nearly follows parabolic law. The mass gains of MoSi2 with the lowest relative density (78.6%) and the highest relative density (94.8%) are increased by 10.390 and 0.135 mg/cm2,respectively. The oxide scale of materials with lower densities is non-protective and makes the oxygen diffusion easy. A dense scale in the material with higher density is formed,which acts as a diffusion barrier to the oxygen atoms to penetrate into the matrix,showing much better high temperature oxidation resistance. The phases distribution of oxidation scale from the outside to the inside is SiO2→Mo5Si3→MoSi2.
