The two-step nucleation of G-phase in ferrite
The two-step nucleation of G-phase in ferrite
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DOI：
10.1016/j.actamat.2016.06.013
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发表时间：
2016-09-01
期刊：
影响因子：
9.4
通讯作者：
Nagai, Y.
中科院分区：
文献类型：
--
作者：
Matsukawa, Y.;Takeuchi, T.;Nagai, Y.
通过结合原子探针层析成像（APT）与透射电子显微镜（TEM），我们已经试图确定的阶段，在该阶段中的溶质团簇转化为化合物的结晶从基体不同，在沉淀的G-相（Ni 16 Si 7 Mn 6）从铁素体固溶体进行等温退火在673 K。基于对溶质团簇的数量密度、尺寸、组成和结构随退火时间的变化的系统分析，发现G相的形核过程分为两步：首先是溶质团簇的自发生长，然后是结构变化转化为G相。此外，发现结构变化通过另一个两步过程发生。团簇生长到临界尺寸（平均直径：类似于2.6 nm）的结束和结构变化的开始之间存在时滞。在孵化期间发生溶质富集内的集群没有进一步的尺寸增长，表明G-相的成核发生在临界尺寸与临界组合物。根据APT、TEM和电子衍射花样的模拟结果，估算出临界成分为Ni_（16）Si_（3.5）（Fe，Cr）（3.5）Mn-6。(C)2016 Acta Materialia Inc.由爱思唯尔有限公司出版。保留所有权利。
By combining atom probe tomography (APT) with transmission electron microscopy (TEM) we have attempted to identify the stage at which solute clusters transform into compounds crystallographically distinct from the matrix, in the precipitation of the G-phase (Ni16Si7Mn6) from ferrite solid solution subjected to isothermal annealing at 673 K. Based on a systematic analysis on the number density, size, composition and structure of solute clusters as a function of annealing time, the nucleation of the G-phase was found to occur via a two-step process: spontaneous growth of solute clusters first, followed by a structural change transforming into the G-phase. Moreover, the structural change was found to occur via another two-step process. There was a time lag between the end of cluster growth to become a critical size (mean diameter: similar to 2.6 nm) and the start of the structural change. During the incubation period solute enrichment occurred inside the clusters without further size growth, indicating that the nucleation of the G-phase occurs at the critical size with a critical composition. Judging from the results of APT, TEM and the simulation of electron diffraction patterns, the critical composition was estimated to be Ni16Si3.5(Fe,Cr)(3.5)Mn-6. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.