420 0

Full metadata record

DC FieldValueLanguage
dc.contributor.advisor김영도-
dc.contributor.author김가언-
dc.date.accessioned2017-11-29T02:29:34Z-
dc.date.available2017-11-29T02:29:34Z-
dc.date.issued2017-08-
dc.identifier.urihttp://hdl.handle.net/20.500.11754/33437-
dc.identifier.urihttp://hanyang.dcollection.net/common/orgView/200000431650en_US
dc.description.abstractFe, Fe-5Y2O3, Fe-10Cr-5Y2O3, Fe-10Cr-1Mo-5Y2O3, and Fe-10Cr-1Mo-0.35Y2O3 (in wt%) powders were mechanically alloyed using a high energy horizontal ball-mill apparatus, and phase transformation behavior of the oxides formed in mechanically alloyed powder was investigated. The attritor was used for the mechanical alloying of the initial powders at 300 rpm with a ball to powder ratio of 10:1 for 48 h in argon atmosphere. The structural evolutions of mechanical alloyed powders were investigated by using X-ray Diffractometer (XRD). An high-resolution Transmission Electron Microscopy (HRTEM) used in order to observed the microstructure and dispersion of the oxide particles. For the samples, mechanically polished to a thickness of ~70 μm and then twin-jet electro-polished to perforation with a solution methly-alcohol and per-chloric acid in 1:9 ratio at -40℃, and 25 V. The formation of oxides particles in mechanically alloyed powders and transformation behavior of oxides were investigated under different temperature by in-situ TEM with Energy Dispersive X-ray Spectroscopy (EDS). The thin film samples on photo-chip membrane for In-situ TEM analysis were prepared by a Focused Ion Beam (FIB) method. The HRTEM and fast Fourier Transformation (FFT) images were evaluated by Gatan digital-micrograph program techniques to identify the crystal structure of nano-sized oxide particles and their crystallographic orientation relationship with the matrix. The results of X-ray diffraction pattern analysis indicated that the Y2O3 diffraction peak disappeared after mechanically alloying process, implying that the Y2O3 dissolved in matrix during mechanical alloying. Non-stoichiometric Y-rich and Fe-rich oxides with sizes of less than 300 nm are observed in the mechanically alloyed Fe-5 wt% Y2O3 powder. The phase transformation behavior of the oxides formed in mechanically alloyed Fe-5 wt% Y2O3 powder is investigated using In-situ TEM. The diffusion and redistribution reactions of the elements in these oxides during heating to above 800℃ were observed, and these reactions result in the formation of a Y3Fe5O12 phase after heating at 1050℃. Thus, it is considered that the Y2O3 powder and some Fe powder are formed from the non-stoichiometric Y-rich and Fe-rich oxides after the mechanical alloying process, and a considerable energy accumulated during the mechanical alloying process leads to a phase transformation of the Y-rich and Fe-rich oxides to YαFeβOγ-type phase during the heating. The mechanically alloyed Fe-5 wt% Y2O3 powders are pressed at 750℃ for 1 h, 850℃ for 1h and 1150℃ for 1h, respectively. The results of X-ray diffraction pattern analysis indicate that the Y2O3 diffraction peak disappear after mechanically alloying process, but Y2O3 and YFe2O4 complex oxide precipitates peak are observed in the powders pressed at 1150℃. The differential scanning calorimetry study results reveal that the formation of precipitates occur at around 1054℃. Based on the transmission electron microscopy analysis result, the oxide particles with a composition of Y-Fe-O are found in the Fe-5 wt% Y2O3 alloy powders pressed at 1150℃. It is thus conclude that the mechanically alloyed Fe-5 wt% Y2O3 powders have no precipitates and the oxide particles in the powders are formed by a high temperature heat-treatment. Fe-10 wt% Cr-5 wt% Y2O3 and Fe-10 wt% Cr-1 wt% Mo-5 wt% Y2O3 mechanically alloyed powders were evaluated to reveal the effect of Cr and Mo addition on the behavior of nano-sized oxide particles. Elongated Cr-rich and Y-rich oxides were observed in the mechanically alloyed powders. During heating to above 700℃, the elongated Cr-rich oxides were dramatically changed to a near-spherical morphology. Cubic-Y2O3, monoclinic-Y2O3 and YFeO3 phases were also found after heat-treatment at 1150℃ for 1 h, indicating that the Y-rich oxide phase was transformed to the cubic-Y2O3, monoclinic-Y2O3 and YFeO3 ones. It is thus concluded that both a morphological change of Cr-rich oxide and a phase transformation of Y-rich oxide during heating of mechanically alloyed powders could be mainly attributed to extremely high energy accumulated by mechanical alloying process. To investigate the size dependence of the orientation relationship of Y2O3-type with the matrix, large Y2O3 particles (>10 nm) and very fine Y2O3 particles (<5 nm) were analyzed using SAED and HRTEM. The inverse FFT images of the fine Y2O3 particle (<5 nm) and the matrix were obtained and combined together to examine the lattice continuity across the interface. The microstructural observation of these mechanically alloyed powders indicated the Y2O3 addition to metal powder acted to refine a grain size and to form non-stoichiometric Y-Fe-O. The crystallization of non-stoichiometric Y-Fe-O particle to YαFeβOγ-type phase occurred above 800℃ by in-situ heating. Fine particles of around 5 nm in size exhibited coherent relationshipwith matrix. It is thus concluded that the Y2O3 powder and some Fe powder are formed from the non-stoichiometric Y-rich and Fe-rich oxides after the mechanical alloying process, and a considerable energy accumulated during the mechanical alloying process leads to a phase transformation of the Y-rich and Fe-rich oxides to YαFeβOγ-type phase during the heating.-
dc.publisher한양대학교-
dc.title철계 산화물분산강화 합금에서 나노산화물의 거동에 관한 연구-
dc.title.alternativeResearch on the Behavior of Nano-sized Oxides in the Fe-based ODS Alloy-
dc.typeTheses-
dc.contributor.googleauthor김가언-
dc.contributor.alternativeauthorKIM, Ga Eon-
dc.sector.campusS-
dc.sector.daehak대학원-
dc.sector.department신소재공학과-
dc.description.degreeDoctor-
Appears in Collections:
GRADUATE SCHOOL[S](대학원) > MATERIALS SCIENCE & ENGINEERING(신소재공학과) > Theses (Master)
Files in This Item:
There are no files associated with this item.
Export
RIS (EndNote)
XLS (Excel)
XML


qrcode

Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.

BROWSE