期刊
SCRIPTA MATERIALIA
卷 199, 期 -, 页码 -出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.scriptamat.2021.113836
关键词
Low-density steel; kappa-carbide; Spinodal decomposition; Atom probe tomography (APT); Transmission electron microscopy (TEM)
类别
资金
- National Natural Science Foundation of China [51974184]
- National MCF Energy R&D Program of China [2018YFE0306102]
- China Scholarship Council [201906890053]
- Conseil Regional du Nord-Pas de Calais
- European Regional Development Fund (ERDF)
The formation of intragranular kappa-carbide in gamma-austenite is found to occur directly in the disordered state, rather than through spinodal decomposition-ordering mechanism. This is due to the similar lattice structure, same composition, and complete coherency between the gamma-austenite matrix and kappa-carbides.
It was usually believed that the formation of intragranular kappa-carbide in gamma-austenite was attributed to spinodal decomposition followed by ordering reaction. In this work, near-atomic scale characterization of an austenite-based Fe-20Mn-9Al-3Cr-1.2C (wt. %) low-density steel, using (high-resolution) scanning transmission electron microscopy and atomic probe tomography, reveals that the initially-formed kappa-carbides (2-3 nm in particle size) are featured with an ordered L'1(2) structure but without detectable chemical partitioning. The Gibbs energy of the FCC phase obtained by thermodynamic calculations al-ways shows a positive curvature (i.e.d(2)G/dx(2) < 0) with the variable contents of Al and C in the temperature range 400-800 degrees C. Both the results demonstrate that the ordered nuclei of kappa-carbide can form directly in the disordered gamma-austenite rather than through the well-known spinodal decomposition-ordering mech-anism. The extremely low nucleation barrier is due to the similar lattice structure, same composition and complete coherency between the gamma-austenite matrix and kappa-carbides. (c) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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