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Vol.44, No.8, 533 ~ 542, 2006
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| Title |
| On the Crystallographic Features of Cr2N Precipitates in High-Nitrogen Austenitic Stainless Steel (5) 5. Neutron diffraction study on the ordered Cr2N superstructure |
| 이태호 Tae Ho Lee , 김성준 Sung Joon Kim , 신은주 Eun Joo Shin , 고목절웅 Setsuo Takakj |
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| Abstract |
| In the fifth part of this study, the ordered structure of Cr2N precipitate was investigated utilizing high-resolution neutron powder diffractometry (HRPD). Based on the Rietveld refinement of neutron diffraction patterns, the ordered Cr2N superstructure was confirmed to be an ordered h.c.p. or trigonal structure (space group: P(-)3 1m) with lattice parameter of a = 4.800 and c = 4.472 Å, as suggested in our previous TEM studies (part Ⅱ ~ Part Ⅳ). Even in perfect ordered state, a partial disordering of nitrogen atoms along caxis was detected, and the occupancies of nitrogen atoms in four different crystallographic position (l(a), 1(b), 2(d) and 2(c) Wyckoff sites) were determined to be 1.00(5), 0.0, 0.74(9) and 0.12(3), respectively. The accurate position of metal atoms was specified to be x = 0.346(8), y = 0 and z = 0.244(6), corresponding to deviation from ideal positions (x = 0.333, y = 0 and z = 0.250). This had a drastic effect on the scattering intensities of (11/33(0)) -type superlattice reflection, whereas the other two types of superlattice reflections were not significantly affected by deviation of metal atoms. The comparison between ideal and measured crystal structure of Cr2N was discussed using computer simulation of selected area diffraction (SAD) patterns. |
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| Key Words |
| Ordered structure, Partial disordering, Deviation of metal atoms, Neutron diffraction and Cr2N |
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