定向凝固Ti-46Al-2Cr-2Nb合金领先相及其生长取向与凝固进程的相关性
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摘要
选择GE公司开发的Ti-46Al-2Cr-2Nb工程合金,采用Bridgman定向凝固技术,通过改变晶体生长距离(5—30 mm)的方法,研究了晶体在渐进生长过程中领先相及其生长取向的演变规律.结果发现,在固定的温度梯度(G=18 K/mm)与生长速度(v=20μm/s)下,定向凝固初始阶段合金的领先相为β相.但随着凝固距离的增加,溶质组元A1在枝晶间的液相中富集程度逐渐增大,导致出现L+β→α包晶反应.随着凝固距离的进一步增加,α和β相的竞争生长加剧,最终导致领先相由β相转变为α相.通过EBSD分析表征了与凝固进程相关的领先相生长取向,在定向凝固初始阶段,领先相β的晶体沿其择优方向〈100〉β生长;在包晶反应过程中,凝固析出的β相和α相遵循{110}β//{0001}α取向关系,由此导致当领先相转变为α相后,晶体的生长方向偏离其择优方向〈0001〉α.
GE alloy Ti-(46一48)Al-2Cr-2Nb(atomic fraction) is well known for its high strength and improved ductility.The primary phase and its growth direction are important in controlling the lamellar direction of GE alloys.However it is greatly affected by solidification conditions.In this work,primary phase and its growth direction have been investigated by carrying out Bridgman-type directional solidification with different growth lengths ranging from 5 to 30 mm on Ti-46Al-2Cr2Nb alloy.It is found that the primary phase is /? at the beginning of directional solidification with constant temperature gradient(G=18 K/mm) and growth rate(^=20 "m/s).With the increase of growth length,A1 gradually concentrates in the liquid between primary dendrites,which leads to the peritectic reaction L+β a.With further increase of the growth length,growth competition between primary(3 phase and peritectic a phase is promoted,leading to gradual transition of primary phases from(3 phase to a phase.The growth direction of primary phase in different stages of solidification has been characterized by EBSD analysis.The results indicate that primary β phase has a growth direction parallel to its preferential growth direction <100>β at the initial stage of solidification.By comparing the growth directions of the grains formed from primary β phase and peritectic a phase,it is found that peritectic a phase related to primary β phase by the {110}β /{0001}a orientatiorelationship.Therefore,as the primary phase has transformed to a phase,the growth direction deviatefrom its preferential growth direction <0001>a at an angle of 45.9°.The growth direction of phase formed after the primary phase transformation is determined not only by the kinetic factorof solidification,but also by the β phase exiting at the beginning of directional solidification.Thesresults provide fundamental references for understanding and controlling the lamellar orientation oGE alloys.
GE alloy Ti-(46一48)Al-2Cr-2Nb(atomic fraction) is well known for its high strength and improved ductility.The primary phase and its growth direction are important in controlling the lamellar direction of GE alloys.However it is greatly affected by solidification conditions.In this work,primary phase and its growth direction have been investigated by carrying out Bridgman-type directional solidification with different growth lengths ranging from 5 to 30 mm on Ti-46Al-2Cr2Nb alloy.It is found that the primary phase is /? at the beginning of directional solidification with constant temperature gradient(G=18 K/mm) and growth rate(^=20 "m/s).With the increase of growth length,A1 gradually concentrates in the liquid between primary dendrites,which leads to the peritectic reaction L+β a.With further increase of the growth length,growth competition between primary(3 phase and peritectic a phase is promoted,leading to gradual transition of primary phases from(3 phase to a phase.The growth direction of primary phase in different stages of solidification has been characterized by EBSD analysis.The results indicate that primary β phase has a growth direction parallel to its preferential growth direction <100>β at the initial stage of solidification.By comparing the growth directions of the grains formed from primary β phase and peritectic a phase,it is found that peritectic a phase related to primary β phase by the {110}β /{0001}a orientatiorelationship.Therefore,as the primary phase has transformed to a phase,the growth direction deviatefrom its preferential growth direction <0001>a at an angle of 45.9°.The growth direction of phase formed after the primary phase transformation is determined not only by the kinetic factorof solidification,but also by the β phase exiting at the beginning of directional solidification.Thesresults provide fundamental references for understanding and controlling the lamellar orientation oGE alloys.
引文
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[17]Fan J L.PhD Dissertation,Harbin Institute of Technology,2012(樊江磊.哈尔滨工业大学博士学位论文,2012)
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[24]Liu D M.PhD Dissertation,Harbin Institute of Technology,2012(刘冬梅.哈尔滨工业大学博士学位论文,2012)
[25]Esaka H,Daimon H,Natsume Y,Ohsasa K,Tamura M G.Mater Trans,2002;43:1312
[26]Singh A K,Muraleedharan K,Banerjee D.Scr Mater,2003;48:767
[2]Kim S E,Lee Y T,Oh M H,Inui H,Yamaguchi M.Intermetallics,2000;8:399
[3]Zollinger J,Lapin J,Daloz D,Combeau H.Interrnetallics,2007;15:1343
[4]Johnson D R,Inui H,Muto S,Omiya Y,Yamanaka T.Acta Mater,2006:54:1077
[5]Lapin J,Pelachova T,Domankova M.Intermetallics,2011;19:814
[6]Liu R C,Wang Z,Liu D,Bai C G,Cui Y Y,Yang R.Acta Metall Sin,2013;49:641(刘仁慈,王震,刘冬,柏春光,崔玉友,杨锐.金属学报,2013;49:641)
[7]Yamanaka T,Johnson D R,Inui H,Yamaguchi M.Intermetallics,1999;7:779
[8]Xiao Z X.PhD Dissertation,Beihang University,2011(肖志霞.北京航空航天大学博士学位论文,2011)
[9]Kim M C,Oh M H,Lee J H,Inui H,Yamaguchi M,Wee D M.Mater Sci Eng,1997;A239-240:570
[10]Li X Z,Sun T,Yu C X,Su Y Q,Cao Y Z,Guo J J,Fu H Z.Acta Metall Sin,2009;45:1479(李新中,孙涛,于彩霞,苏彦庆,曹勇智,郭景杰,傅恒志.金属学报,2009;45:1479)
[11]Yang L L,Zheng L J,Xiao Z X,Yan J,Zhang H.Acta Metall Sin,2010;46:879(杨莉莉,郑立静,肖志霞,闰洁,张虎.金属学报,2010;46:879)
[12]Xiao Z X,Zheng L J,Yang L L,Yan J,Zhang H.Acta Metall Sin,2010;46:1223(肖志霞,郑立静,杨莉莉,闰洁,张虎.金属学报,2010;46:1223)
[13]Thomas M,Bacos M T.High Temp Mater,2011;3:7
[14]Nie G.PhD Dissertation,Harbin Institute of Technology,2012(聂革.哈尔滨工业大学博士学位论文,2012)
[15]Xiao Z X,Zheng L J,Yan J,Yang L L,Zhang H.J Cryst Growth,2011;324:309
[16]Xiao Z X,Zheng L J,Wang L,Yang L L,Zhang H.J Wuhan Univ Technol,2011;26:197
[17]Fan J L.PhD Dissertation,Harbin Institute of Technology,2012(樊江磊.哈尔滨工业大学博士学位论文,2012)
[18]Daloz D,Hecht U,Zollinger J,Combeau H,Hazotte A,Zaloznik M.Intermetallics,2011;19:749
[19]Fu H Z,Guo J J,Liu L,Li J S.Directional Solidification and Processing of Advanced Materials.Beijing:Science Press,2008:356(傅恒志,郭景杰,刘林,李金山.先进材料定向凝固.北京:科学出版社,2008:356)
[20]Charpentier M,Daloz D,Gautier E,Lesoult G,Hazotte A,Grange M.Metall Mater Trans,2003;34A:2139
[21]Li Y X,Wu A P.Principle ofMaterials Processing.Beijing:Tsinghua University Press,2005:93(李言祥,吴爱萍.材料加工原理.北京:清华大学出版社,2005:93)
[22]Glicksman E.Principles of Solidification:An Introduction to Modern Casting and Crystal Growth Concepts.New York:Springer,2011:347
[23]Su Y Q,Liu C,Li X Z,Guo J J,Li B S,Jia J,Fu H Z.Intermetallics,2005;13:267
[24]Liu D M.PhD Dissertation,Harbin Institute of Technology,2012(刘冬梅.哈尔滨工业大学博士学位论文,2012)
[25]Esaka H,Daimon H,Natsume Y,Ohsasa K,Tamura M G.Mater Trans,2002;43:1312
[26]Singh A K,Muraleedharan K,Banerjee D.Scr Mater,2003;48:767