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Acta Metall Sin  2019, Vol. 55 Issue (5): 593-600    DOI: 10.11900/0412.1961.2018.00506
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Effect of Mn Composition on the Nanometer Cu-Rich Phase of Fe-Cu-Mn Alloy by Phase Field Method
Baojun ZHAO,Yuhong ZHAO(),Yuanyang SUN,Wenkui YANG,Hua HOU
1. School of Materials Science and Engineering, North University of China, Taiyuan 030051, China
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Abstract  

The precipitation of nanometer Cu-rich phase can be observed in Fe-Cu alloy systems during isothermal ageing. The existence of Cu-rich phase is one of the reasons for the embrittlement of reactor pressure vessel (RPV) steel. The phase-field method applies a set of field variables defined by functions of space and time to describe the temporal evolution of composition and structural parameter, characterizing microstructure evolution during phase transformation. This work uses phase-field model to simulate the three-dimensional morphology, the volume fraction, number density and average particle radius of Cu-rich phase in Fe-Cu-Mn alloy at 823 K. The chemical free energy is derived from the thermodynamic database of the calculated phase diagram (CALPHAD), so the microstructure evolution of precipitation changes are directly corresponded to phase diagram of the real alloy system. The simulation results show that nanometer Cu-rich phase are formed by the spinodal decomposition mechanism in the early stage of phase separation. Meanwhile, Mn atoms segregate to the center of the Cu-rich phase. During the process of Ostwald coarsening, Mn atoms migrate from core to the interface of Cu-rich phase, finally forming Mn-rich ring distributed in the exterior of Cu-rich phase. Its existence can decrease the rates of diffusion growth and coarsening of Cu-rich phase. The Cu-rich phase is bcc structure and disperses in the matrix with spherical shape in the early stage of ageing. As the Cu-rich phase continues to grow, it will transform into fcc structure with ellipsoid or rod shapes. Meanwhile, increasing Mn content of Fe-Cu-Mn alloy accelerates the precipitation of Cu-rich phase and facilitates the growth and coarsening of Cu-rich phase.

Key words:  Fe-Cu alloy system      nanometer Cu-rich phase      RPV steel      phase-field simulation      spinodal decomposition     
Received:  07 November 2018     
ZTFLH:  TG292  
Fund: National Natural Science Foundation of China(U1610123);National Natural Science Foundation of China(51674226);National Natural Science Foundation of China(51574206);National Natural Science Foundation of China(51774254);National Natural Science Foundation of China(51701187);Science and Technology Major Project of Shanxi Province(MC2016-06)
Corresponding Authors:  Yuhong ZHAO     E-mail:  zhaoyuhong@nuc.edu.cn

Cite this article: 

Baojun ZHAO,Yuhong ZHAO,Yuanyang SUN,Wenkui YANG,Hua HOU. Effect of Mn Composition on the Nanometer Cu-Rich Phase of Fe-Cu-Mn Alloy by Phase Field Method. Acta Metall Sin, 2019, 55(5): 593-600.

URL: 

https://www.ams.org.cn/EN/10.11900/0412.1961.2018.00506     OR     https://www.ams.org.cn/EN/Y2019/V55/I5/593

ParameterValueUnit
kc,kηkc=5.0×10-15,kη=1.0×10-15J·m2·mol-1
Vm7.09×10-6m3·mol-1
T823K
Y214GPa
Lx×Ly×Lz32×32×32nm3
SiSCu=3.29×10-2,SMn=5.22×10-4
W5.0×103J·mol-1

Di0,φφ=α,γ

DCu0,α=4.7×10-5,DCu0,γ=4.3×10-5

DMn0,α=1.49×10-4, DMn0,γ=1.78×10-5

m2·s-1

Qi0,φφ=α,γ

QCu0,α=2.44×105, QCu0,γ=2.80×105

QMn0,α=2.33×10-5, QMn0,γ=2.64×105

J·mol-1

Table 1  The parameters used in the phase field model[31]
Fig.1  Morphology evolutions of Cu precipitates in Fe-Cu-Mn alloys with 1% (a1~d1), 3% (a2~d2) and 5% (a3~d3) Mn aged at 823 K and ageing time of t*=3000 (a1~a3), t*=3500 (b1~b3), t*=5000 (c1~c3) and t*=7500 (d1~d3)Color online
Fig.2  Concentration distribution curves of Cu and Mn at defined horizontal line in Fe-Cu-Mn alloys with 1% (a), 3% (b) and 5% (c) Mn aged for t*=3000 at 823 K
Fig.3  Concentration distribution curves of Cu precipitates at defined horizontal line in Fe-Cu-Mn alloys with 1% (a) and 5% (b) Mn aged at 823 K for different time
Fig.4  Structure order parameter of Cu precipitates at defined horizontal line in Fe-Cu-Mn alloys with 1% (a), 3% (b) and 5% (c) Mn aged at 823 K for different time
Fig.5  Variation of volume fraction of Cu-rich phase in Fe-Cu-Mn alloys with 1%, 3% and 5% Mn aged at 823 K as a function of ageing time
Fig.6  The particle number density of the Cu-rich phase in Fe-Cu-Mn alloys with 1%, 3% and 5% Mn aged at 823 K as a function of ageing time
Fig.7  The particle number density of the Cu-rich phase in Fe-Cu-Mn alloys with 1%, 3% and 5% Mn aged at 823 K as a function of ageing time
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