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金属学报  2019, Vol. 55 Issue (4): 511-520    DOI: 10.11900/0412.1961.2018.00166
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奥氏体析出相激发形核的原位TEM研究
杜娟1,程晓行2,杨天南2,陈龙庆2,3,Mompiou Frédéric4,张文征1()
1. 清华大学材料学院教育部先进材料重点实验室 北京 100084
2. Department of Materials Science and Engineering, The Pennsylvania State University, University Park,PA 16802, USA
3. 清华大学材料学院新型陶瓷与精细工艺国家重点实验室 北京 100084
4. CEMES-CNRS and Université de Toulouse, 29 rue J. Marvig, 31055 Toulouse, France
In Situ TEM Study on the Sympathetic Nucleation of Austenite Precipitates
Juan DU1,Xiaoxing CHENG2,Tiannan YANG2,Longqing CHEN2,3,Frédéric Mompiou4,Wenzheng ZHANG1()
1. Key Laboratory of Advanced Materials MOE, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China
2. Department of Materials Science and Engineering, The Pennsylvania State University, University Park,PA 16802, USA
3. State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China
4. CEMES-CNRS and Université de Toulouse, 29 rue J. Marvig, 31055 Toulouse, France
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摘要: 

利用原位透射电镜(TEM)观察双相不锈钢中奥氏体析出相变过程,发现了端-面连接的奥氏体激发形核现象。定量表征结果表明,激发形核奥氏体和先驱奥氏体与母相铁素体的位向关系都接近N-W,但属于不同的位向关系,且在不同的Bain环上。基于弹性相互作用能和界面能解释了激发形核奥氏体的择优晶体学取向,计算结果表明,先驱奥氏体与不同Bain环上激发形核奥氏体的弹性相互作用能为负值,且相邻奥氏体之间可以形成孪晶取向关系及共格孪晶界。

关键词 原位透射电镜激发形核奥氏体析出相弹性相互作用能    
Abstract

Duplex stainless steels (DSSs) are widely used for chemical industry, marine construction and power plants, due to the beneficial combination of ferrite and austenite properties: high strength with a desirable toughness and good corrosion resistance. The sympathetic nucleation (SN) of intragranular austenite precipitates has been frequently observed in DSS. This type of nucleation, which occurs in a considerable variety of steels and titanium alloys, has a great effect on the morphological arrangement of precipitates and hence the mechanical properties of metallic materials. Therefore, understanding the SN mechanism of austenite precipitates is essential to knowledge based material design of the microstructure in DSS. Three types of morphological arrangement, i.e., face-to-face, edge-to-edge and edge-to-face SN of austenite precipitates, have been identified in previous investigations on DSS. The adjacent grains of face-to-face and edge-to-edge sympathetically nucleated austenite have approximately the identical orientations, with a small-angle boundary between two austenite crystals. However, as regards to the edge-to-face SN, the lacking of crystallographic features of adjacent austenite precipitates obstructs the understanding of the mechanism for the edge-to-face SN. Moreover, it is usually difficult to distinguish between SN and hard impingement following nucleation at separate sites in conventional experimental observations. Thus, in the present work, the typical morphology of edge-to-face SN of austenite precipitates was directly observed at 725 ℃ in a DSS using in situ TEM. The orientation relationship (OR) between the sympathetically nucleated austenite precipitate and ferrite matrix is determined through analysis of Kikuchi lines. Since the long axes of austenite precipitates parallel to the invariant line are restricted in the thin TEM foil, there are only four types of austenite with different near N-W ORs and cystallographically inequivalent long axes. This work reveals that the ORs of sympathetically nucleated austenite grains belong to different Bain groups with those of the pre-formed austenites. The explanation for the OR selection is provided based on two factors favoring SN, namely the reduction of elastic interaction strain energy and the interfacial energy. The local stress generated by the semi-coherent pre-formed austenite was calculated by Eshelby inclusion method. The local stress field accompanying with the pre-formed austenite assists the subsequent nucleation and growth of sympathetically nucleated austenite. It shows that the elastic interaction energy for the sympathetically nucleated austenite of particular OR is negative. In addition, the pre-formed austenite and the sympathetically nucleated austenite grain are twin related. This indicates that the nucleation barrier associated with SN of austenite with selected OR is comparably lower than other candidates. Hence, the austenite precipitate with a specific OR is preferred during SN.

Key wordsin situ TEM    sympathetic nucleation    austenite precipitate    elastic interaction energy
收稿日期: 2018-04-28     
ZTFLH:  TG113  
基金资助:国家自然科学基金项目(No.51471097)
通讯作者: 程晓行,张文征     E-mail: zhangwz@tsinghua.edu.cn
Corresponding author: Xiaoxing CHENG,Wenzheng ZHANG     E-mail: zhangwz@tsinghua.edu.cn
作者简介: 杜 娟,女,1990年生,博士生

引用本文:

杜娟, 程晓行, 杨天南, 陈龙庆, Mompiou Frédéric, 张文征. 奥氏体析出相激发形核的原位TEM研究[J]. 金属学报, 2019, 55(4): 511-520.
Juan DU, Xiaoxing CHENG, Tiannan YANG, Longqing CHEN, Fré, dé, ric Mompiou, Wenzheng ZHANG. In Situ TEM Study on the Sympathetic Nucleation of Austenite Precipitates. Acta Metall Sin, 2019, 55(4): 511-520.

链接本文:

https://www.ams.org.cn/CN/10.11900/0412.1961.2018.00166      或      https://www.ams.org.cn/CN/Y2019/V55/I4/511

PhaseC11C12C44
γ204.6137.7126.2
α236.9140.6116.0
表1  计算中采用的单晶奥氏体(γ)和铁素体(α)的各向异性弹性常数[28]
图1  原位加热时奥氏体γ2在先驱奥氏体γ1惯习面激发形核后长大的早期过程视频截图
图2  原位冷却后端-面激发形核连接的奥氏体γ1~γ4形貌
图3  测定奥氏体γ1与母相铁素体位向关系时两相Kikuchi花样的标定
图4  迹线法测定奥氏体γ1长轴取向时γ1形貌和铁素体Kikuchi花样的标定
图5  测定奥氏体γ1惯习面取向时铁素体Kikuchi花样的标定
Parameterγ1γ2γ3γ4

OR

(011)b~∥(111)f

0.3°

(011)b~∥(111)f

0.2°

(01ˉ1)b~∥(111)f

0.5°

(01ˉ1)b~∥(111)f

0.2°

[100]b~∥[11ˉ0]f

1.6°

[1ˉ00]b~∥[11ˉ0]f

1.6°

[100]b~∥[11ˉ0]f

0.7°

[1ˉ00]b~∥[11ˉ0]f

1.1°

Long axis[0.32 0.78ˉ 0.53]b[0.26 0.53ˉ 0.81]b[0.05ˉ 0.49 0.87]b[0.22ˉ 0.82 0.53]b

Habit plane

(0.08ˉ 0.54 0.84)b

(0.41 0.54 0.73)f

-

-

-

-

(0.13 0.52ˉ 0.84)b

(0.37 0.56 0.74)f

表2  激发形核奥氏体γ1~γ4的晶体学特征
图6  奥氏体γ1~γ4长轴(Δ)及TEM样品膜面法向(fn, +)在[001]b为投影中心的极图
ParameterO-line solution for γ1O-line solution for γ4
xin[0.32 0.79ˉ 0.52]b[0.21ˉ 0.83 0.52]b

OR

(111)b~∥(011)f, 0.4°(111)b~∥(01ˉ1)f, 0.4°
[100]b~∥[11ˉ0]f, 2.3°[1ˉ00]b~∥[11ˉ0]f, 1.5°
Habit plane (p1)(0.11ˉ 0.51 0.85)b(0.07 0.52ˉ 0.85)b
b[100]b|[11ˉ0]f[100]b|[11ˉ0]f
D / nm2.22.2
d1[0.95 0.19ˉ 0.22]b[0.98ˉ 0.13 0.15]b
m11.10931.6621
表3  原位先驱奥氏体γ1和γ4的O线解计算结果[34]及其宏观不变平面应变(P1)的相关参量
图7  先驱奥氏体应力场计算中的参数设定示意图
图8  激发形核奥氏体与先驱奥氏体周围母相的弹性相互作用能密度分布图
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