旋节分解
奥氏体
材料科学
碳化物
成核
冶金
微观结构
旋节
结晶学
热力学
相(物质)
化学
物理
有机化学
作者
Jianlei Zhang,Yueshan Jiang,Weisen Zheng,Yuxiang Liu,Ahmed Addad,Gang Ji,Changjiang Song,Qijie Zhai
标识
DOI:10.1016/j.scriptamat.2021.113836
摘要
It was usually believed that the formation of intragranular κ-carbide in γ-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 κ-carbides (2-3 nm in particle size) are featured with an ordered L′12 structure but without detectable chemical partitioning. The Gibbs energy of the FCC phase obtained by thermodynamic calculations always shows a positive curvature (i.e. d2Gdx2 < 0) with the variable contents of Al and C in the temperature range 400-800 °C. Both the results demonstrate that the ordered nuclei of κ-carbide can form directly in the disordered γ-austenite rather than through the well-known spinodal decomposition-ordering mechanism. The extremely low nucleation barrier is due to the similar lattice structure, same composition and complete coherency between the γ-austenite matrix and κ-carbides.
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