低碳低合金钢中纳米富Cu相的析出特征
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摘要
低碳低合金钢样品经880℃加热0.5 h后水淬,再进行660℃保温10 h的调质处理,最后分别在370℃和400℃等温时效3000 h和2000 h后,利用高分辨透射电镜(HRTEM)、能谱仪(EDS)以及三维原子探针(3DAP)相结合的方法,分析低碳低合金钢中析出的纳米富Cu相的晶体结构和Cu、Mn、Ni原子分布特征。在HRTEM图像中观察到长轴约9.3 nm,短轴约6.1 nm的短棒状纳米富Cu相,其结构为正交9R结构且互为孪生关系,其中9R结构与α-Fe基体存在一定位向关系,即:(011)_(bcc)//(114)_(9R),[111]_(bcc)//[110]_(9R)。说明Cu早期析出时可能由bcc结构优先转变孪晶正交9R结构,而不是直接转变为fcc结构。利用3DAP技术可以看出,在富Cu原子团簇形核长大过程中,Mn、Ni原子会偏聚在Cu与α-Fe基体的界面处,造成这种现象,除了富Cu原子团簇在富Ni、富Mn区域形核且在长大过程不断向外排挤Mn、Ni原子外,Cu与α-Fe基体界面存在较高的共格畸变能也会造成Mn、Ni原子的偏聚,进而阻碍富Cu原子团簇的长大。
Low carbon low alloy steel samples were heat treated at 880 ℃ for 0. 5 h and water quenched,then tempered at 660 ℃ for 10 h,finally isothermally aged at 370 ℃ and 400 ℃ for 3000 h and 2000 h,respectively. The crystal structure of Cu-rich nanophase precipitates and distribution of Cu,Mn,Ni atoms in the steel were analyzed by using high resolution transmission electron microscope(HRTEM),energy dispersive spectroscopy(EDS) and three dimensional atom probe(3DAP). The short rod-like Cu-rich nanophase,with its long axis and the short axis being about 9. 3 nm and about 6. 1 nm respectively,was observed in HRTEM micrographs. These nanophase precipitates have orthogonal 9 R structure with mutual twin relationship,and have certain orientation relationship with the α-Fe matrix,ie.,(011)_(bcc)//(114)_(9R),[111]_(bcc)//[110]_(9R). It indicates that the early precipitation of Cu is not direct transformation to the fcc structure,but preferentially transformed into the orthogonal structure of 9R with twin relationship. It is found by 3DAP analysis that Mn,Ni atoms will continue to segregate at the interface between Cu and the α-Fe matrix during the nucleation and growth process of Cu-rich clusters. The reason is that,besides Cu clusters nucleation at the rich Ni and rich Mn area that Mn and Ni atoms are pushed outwards continuously during growth process of Cu atom clusters nucleated at the rich Ni region,the segregation of Mn and Ni atoms is also resulted from higher coherent strain energy between Cu and the α-Fe matrix,which can hinder the growth of Cu-rich clusters.
Low carbon low alloy steel samples were heat treated at 880 ℃ for 0. 5 h and water quenched,then tempered at 660 ℃ for 10 h,finally isothermally aged at 370 ℃ and 400 ℃ for 3000 h and 2000 h,respectively. The crystal structure of Cu-rich nanophase precipitates and distribution of Cu,Mn,Ni atoms in the steel were analyzed by using high resolution transmission electron microscope(HRTEM),energy dispersive spectroscopy(EDS) and three dimensional atom probe(3DAP). The short rod-like Cu-rich nanophase,with its long axis and the short axis being about 9. 3 nm and about 6. 1 nm respectively,was observed in HRTEM micrographs. These nanophase precipitates have orthogonal 9 R structure with mutual twin relationship,and have certain orientation relationship with the α-Fe matrix,ie.,(011)_(bcc)//(114)_(9R),[111]_(bcc)//[110]_(9R). It indicates that the early precipitation of Cu is not direct transformation to the fcc structure,but preferentially transformed into the orthogonal structure of 9R with twin relationship. It is found by 3DAP analysis that Mn,Ni atoms will continue to segregate at the interface between Cu and the α-Fe matrix during the nucleation and growth process of Cu-rich clusters. The reason is that,besides Cu clusters nucleation at the rich Ni and rich Mn area that Mn and Ni atoms are pushed outwards continuously during growth process of Cu atom clusters nucleated at the rich Ni region,the segregation of Mn and Ni atoms is also resulted from higher coherent strain energy between Cu and the α-Fe matrix,which can hinder the growth of Cu-rich clusters.
引文
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[17]Xu Gang,Chu Dafeng,Cai Linlin,et al.Investigation on the precipitation and structural evolution of Cu-rich nanophase in RPV model steel[J].Acta Metallurgica Sinica,2011,47(7):905-911.
[18]Bouar Y L.Atomitic study of the coherency loss during the bcc-9R transformation of small copper precipitates in ferritic steels[J].Acta Materialia,2001,49:2661-2669.
[2]Chen Bolin,Wang Wei,Xie Hui,et al.Phase transformation of Cu-rich precipitates from 9R to 3R variant via ledges mechanism in ferritic steel containing copper[J].Journal of Microscopy,2015,262(1):123-127.
[3]Heo Y U,Kim Y K,Kim J S,et al.Phase transformation of Cu precipitates from bcc to fcc in Fe-3Si-2Cu alloy[J].Acta Materialia,2013,61(2):519-528.
[4]Othen P J,Jenkins M L,Smith G D W.High-resolution electron microscopy studies of the structure of Cu precipitates inα-Fe[J].Philosophical Magazine A,1994,70(1):1-24.
[5]Othen P J,Jenkins M L,Smith G D W,et al.Transmission electron microscopy investigations of the structure of copper precipitates in thermally-aged Fe-Cu and Fe-Cu-Ni[J].Philosophical Magazine Letters,1991,64(6):383-391.
[6]Monzen R,Iguchi M.Structural changes of 9R copper precipitates in an aged Fe-Cu alloy[J].Philosophical Magazine Letters,2010,80(3):137-148.
[7]Wen Y R,Hirata A,Zhang Z W,et al.Microstructure characterization of Cu-rich nanoprecipitates in a Fe-2.5Cu-1.5Mn-4.0Ni-1.0Al multicomponent ferritic alloy[J].Acta Materialia,2013,61(6):2133-2147.
[8]Cerezo A,Hirisawa S,Rozdilsky I,et al.Combined atomic-scale modeling and experimental studies of nucleation in the solid state[J].Phil Trans R Soc Lond,2003,361(1804):463-476.
[9]周邦新,王均安,刘庆东,等.Ni对PRV模拟钢中富Cu原子团簇析出的影响[J].中国材料进展,2011,30(5):1-6.Zhou Bangxin,Wang Junan,Liu Qingdong,et al.Effect of nickel alloying element on the precipitation of Cu-rich clusters in RPV model steel[J].Materials China,2011,30(5):1-6.
[10]徐刚,楚大锋,蔡琳玲,等.RPV模拟钢中纳米富Cu相的析出与结构演化[J].金属学报,2011,47(7):905-911.Xu Gang,Chu Dafeng,Cai Linlin,et al.Investigation on the precipitation and structural evolution of Cu-rich nanophase in RPV model steel[J].Acta Metallurgica Sinica,2011,47(7):905-911.
[11]Monzen R,Jenkins M L,Sutto A P.The bcc-to-9R martensitic transformation of Cu precipitates and the relaxation process of elastic strains in an Fe-Cu alloy[J].Philosophical Magazine A,2000,80(3):711-723.
[12]Hardouin D H A,Doole R C,Jenkins M L,et al.A high-resolution electron microscopy study of copper precipitation in Fe-1.5wt%Cu under electron irradiation[J].Philosophical Magazine Letters,1995,71(6):325-333.
[13]Feng Liu,Zhou Bangxin,Peng Jianchao,et al.Crystal structure evolution of the Cu-rich nano precipitates from bcc to 9R in reactor pressure vessel model steel[J].Acta Metallurgica Sinica,2013,26(6):707-712.
[14]Gorbatov O I,Gornostyrev Y N,Korzhavyi P A,et al.Effect of Ni and Mn on the formation of Cu precipitates[J].Scripta Materialia,2015,102:11-14.
[15]Styman P D,Hyde J M,Wilford K,et al.Characterisation of interfacial segregation to Cu-enriched precipitates in two thermally aged reactor pressure vessel steel welds[J].Ultramicroscopy,2015,159:292-298.
[16]Wen Y R,Li Y P,Hirata A,et al.Synergistic alloying effect on microstructural evolution and mechanical properties of Cu precipitationstrengthened ferritic alloys[J].Acta Materialia,2013,61(20):7726-7740.
[17]Xu Gang,Chu Dafeng,Cai Linlin,et al.Investigation on the precipitation and structural evolution of Cu-rich nanophase in RPV model steel[J].Acta Metallurgica Sinica,2011,47(7):905-911.
[18]Bouar Y L.Atomitic study of the coherency loss during the bcc-9R transformation of small copper precipitates in ferritic steels[J].Acta Materialia,2001,49:2661-2669.