CM247LC单晶高温合金中MC碳化物对γ/γ′共晶反应的影响
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摘要
在0.2 mm/min的抽拉速率下对高温合金CM247LC进行了单晶定向凝固实验,观察分析了水淬的糊状区内的组织。结果显示,合金凝固时首先形成g枝晶,然后初生MC碳化物在g枝晶尖端稍后的位置开始形成,γ/γ′共晶在凝固最后阶段析出。值得注意的是,γ/γ′共晶反应是以化学成分和晶体结构都完全不同的MC碳化物作为异质形核核心,而不是依附在形核条件更好的g相上。检测结果表明,在MC碳化物基底上形成的γ/γ′共晶体具有杂乱的晶体取向,与单晶g相基体的取向完全不同,说明宏观上为单晶体的高温合金铸件实际上可能含有许多微小杂晶晶粒,使得铸件的单晶性受到影响。
The structure formation of superalloys is very complicated because of their multicomponent composition and multiphase transition processing. Duo to the limitation of some pre-conditions, the structure formation can not be accurately determined by thermodynamic calculation method. Knowledge about the structure is critical for the design of the following heat treatment process. In this work, a single crystal(SC) sample of superalloy CM247 LC was directional solidified in a labor Bridgman furnace with a pulling rate of 0.2 mm/min and then water quenched, to investigate the solidification sequence including MC carbide and γ/γ′-eutectic. It was observed that the g-phase is firstly formed in the form of dendrites; it is then followed by the homogeneously precipitation of MC carbides from the liquid behind dendrite tips.Near the end of solidification the interdendritic residual liquid transits into γ/γ′-eutectics. It is interesting to found that the γ/γ′ eutectics do not nucleate on the existing g-phase, but preferably on the MC carbides which have completely different chemical composition and crystal structure. The result of EBSD examination indicates that the γ/γ′ eutectics formed on the MC substrates have random crystal orientations compared to the SC g-matrix, exhibiting the misoriented multi-crystal microstructure in the so called "single crystal" superalloy casting.
The structure formation of superalloys is very complicated because of their multicomponent composition and multiphase transition processing. Duo to the limitation of some pre-conditions, the structure formation can not be accurately determined by thermodynamic calculation method. Knowledge about the structure is critical for the design of the following heat treatment process. In this work, a single crystal(SC) sample of superalloy CM247 LC was directional solidified in a labor Bridgman furnace with a pulling rate of 0.2 mm/min and then water quenched, to investigate the solidification sequence including MC carbide and γ/γ′-eutectic. It was observed that the g-phase is firstly formed in the form of dendrites; it is then followed by the homogeneously precipitation of MC carbides from the liquid behind dendrite tips.Near the end of solidification the interdendritic residual liquid transits into γ/γ′-eutectics. It is interesting to found that the γ/γ′ eutectics do not nucleate on the existing g-phase, but preferably on the MC carbides which have completely different chemical composition and crystal structure. The result of EBSD examination indicates that the γ/γ′ eutectics formed on the MC substrates have random crystal orientations compared to the SC g-matrix, exhibiting the misoriented multi-crystal microstructure in the so called "single crystal" superalloy casting.
引文
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[2]He L Z,Zheng Q,Sun X F,et al.Effect of carbides on the creep properties of a Ni-base superalloy M963[J].Mater.Sci.Eng.,2005,A397:297
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[14]Chen J,Lee J H,Jo C Y,et al.MC carbide formation in directionally solidified MAR-M247 LC superalloy[J].Mater.Sci.Eng.,1998,A247:113
[15]Sun W R,Lee J H,Seo S M,et al.The eutectic characteristic of MC-type carbide precipitation in a DS nickel-base superalloy[J].Mater.Sci.Eng.,1999,A271:143
[16]Chen J,Huang B Y,Lee J H,et al.Carbide formation process in directionally solidified MAR-M247 LC superalloy[J].J.Mater.Sci.Technol.,1999,15:48
[17]Huang H E,Koo C H.Characteristics and mechanical properties of polycrystalline CM 247 LC superalloy casting[J].Mater.Trans.,2004,45:562
[18]Szczotok A,Rodak K.Microstructural studies of carbides in MARM247 nickel-based superalloy[J].IOP Conf.Ser.:Mater.Sci.Eng.,2012,35:012006
[19]D'Souza N,Dong H B.Solidification path in third-generation Nibased superalloys,with an emphasis on last stage solidification[J].Scr.Mater.,2007,56:41
[20]Liang Y J,Li J,Li A,et al.Solidification path of single-crystal nickel-base superalloys with minor carbon additions under laser rapid directional solidification conditions[J].Scr.Mater.,2017,127:58
[21]Durand-Charre M,translated by Davidson J H.The Microstructure of Superalloys[M].Amsterdam:Gordon and Breach Science Publishers,1997:30
[22]Zou J,Wang H P,Doherty R,et al.Solidification behavior and microstructure formation in a cast Nickel based superalloy:Experiment and modeling[A].Superalloys 1992[C].Warrendale:TMS,1992:165
[23]D'Souza N D,Dong H B.An analysis of solidification path in the Ni-base superalloy,CMSX10K[A].Superalloys 2008[C].Warrendale:TMS,2008:261
[24]Zou J,Wang H P,Doherty R,et al.Solidification behavior and microstructure formation in a cast nickel based superalloy:Experiment and modeling[A].Superalloys 1992[C].Warrendale:TMS,1992:165
[25]Warnken N,Ma D,Mathes M,et al.Investigation of eutectic island formation in SX superalloys[J].Mater.Sci.Eng.,2005,A413-414:267
[2]He L Z,Zheng Q,Sun X F,et al.Effect of carbides on the creep properties of a Ni-base superalloy M963[J].Mater.Sci.Eng.,2005,A397:297
[3]Yang J X,Zheng Q,Sun X F,et al.Topologically close-packed phase precipitation in a nickel-base superalloy during thermal exposure[J].Mater.Sci.Eng.,2007,A465:100
[4]Harris K,Erickson G L.Single crystal(single grain)alloy[P].US Pat,4582548,1986
[5]Ross E W,Wukusick C S,King W T.Nickel-based superalloys for producing single crystal articles having improved tolerance to low angle grain boundaries[P].US Pat,5399313,1995
[6]Wasson A J,Fuchs G E.Microstructural evolution of a carbon modified single crystal Ni-base superalloy[J].Mater.Charact.,2012,74:11
[7]Mihalisin J R,Corrigan J,Baker R J,et al.Clean single crystal nickel base superalloy[P].US Pat,5549765,1996
[8]Tin S,Pollock T M,Murphy W.Stabilization of thermosolutal convective instabilities in Ni-based single-crystal superalloys:Carbon additions and freckle formation[J].Metall.Mater.Trans.,2001,32A:1743
[9]Cutler E R,Wasson A J,Fuch G E.Effect of minor alloying additions on the solidification of single-crystal Ni-base superalloys[J].J.Cryst.Growth,2009,311:3753
[10]Tin S,Pollock T M,King W T.Carbon additions and grain defect formation in high refractory nickel-base single crystal superalloy[A].Superalloys 2000[C].Warrendale:TMS,2000:201
[11]Tin S,Pollock T M.Stabilization of thermosolutal convective instabilities in Ni-based single-crystal superalloys:Carbide precipitation and Rayleigh numbers[J].Metall.Mater.Trans.,2003,34A:1953
[12]Liu L,Fu H Z,Shi Z X.Relationship between primary morphology and crystal structure of carbides growing in superalloys[J].Acta Metall.Sin.(Engl.Ed.),1990,3:46
[13]Liu L,Sommer F,Fu H Z.Effect of solidification conditions on MC carbides in a Nickel-base superalloy in IN 738-LC[J].Scr.Metall.Mater.,1994,30:587
[14]Chen J,Lee J H,Jo C Y,et al.MC carbide formation in directionally solidified MAR-M247 LC superalloy[J].Mater.Sci.Eng.,1998,A247:113
[15]Sun W R,Lee J H,Seo S M,et al.The eutectic characteristic of MC-type carbide precipitation in a DS nickel-base superalloy[J].Mater.Sci.Eng.,1999,A271:143
[16]Chen J,Huang B Y,Lee J H,et al.Carbide formation process in directionally solidified MAR-M247 LC superalloy[J].J.Mater.Sci.Technol.,1999,15:48
[17]Huang H E,Koo C H.Characteristics and mechanical properties of polycrystalline CM 247 LC superalloy casting[J].Mater.Trans.,2004,45:562
[18]Szczotok A,Rodak K.Microstructural studies of carbides in MARM247 nickel-based superalloy[J].IOP Conf.Ser.:Mater.Sci.Eng.,2012,35:012006
[19]D'Souza N,Dong H B.Solidification path in third-generation Nibased superalloys,with an emphasis on last stage solidification[J].Scr.Mater.,2007,56:41
[20]Liang Y J,Li J,Li A,et al.Solidification path of single-crystal nickel-base superalloys with minor carbon additions under laser rapid directional solidification conditions[J].Scr.Mater.,2017,127:58
[21]Durand-Charre M,translated by Davidson J H.The Microstructure of Superalloys[M].Amsterdam:Gordon and Breach Science Publishers,1997:30
[22]Zou J,Wang H P,Doherty R,et al.Solidification behavior and microstructure formation in a cast Nickel based superalloy:Experiment and modeling[A].Superalloys 1992[C].Warrendale:TMS,1992:165
[23]D'Souza N D,Dong H B.An analysis of solidification path in the Ni-base superalloy,CMSX10K[A].Superalloys 2008[C].Warrendale:TMS,2008:261
[24]Zou J,Wang H P,Doherty R,et al.Solidification behavior and microstructure formation in a cast nickel based superalloy:Experiment and modeling[A].Superalloys 1992[C].Warrendale:TMS,1992:165
[25]Warnken N,Ma D,Mathes M,et al.Investigation of eutectic island formation in SX superalloys[J].Mater.Sci.Eng.,2005,A413-414:267