新型粉末高温合金多火次等温锻造过程中晶粒细化机制
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摘要
为探索多火次等温锻造对新型粉末高温合金晶粒细化的影响,本文对实验合金进行了每火次变形量40%左右的三火次等温锻造,采用商用有限元软件DEFORM 2D模拟锻造过程中的等效应变分布图,采用电子背散射衍射技术对各火次后的锻坯进行显微组织观察和分析.研究表明:等温锻造过程中,锻坯轴向剖面大致分为三个区域,位于上、下两端面附近的Ⅰ区变形量最小,位于两侧附近的Ⅱ区次之,位于剖面中心的Ⅲ区变形程度最大.经过三火次等温锻造后,锻坯Ⅱ、Ⅲ区再结晶充分,获得等轴细晶组织,平均晶粒尺寸2～3μm.然而Ⅰ区形成再结晶不完全的"项链"组织,在变形晶粒周围分布大量细小的再结晶晶粒,变形晶粒内小角度晶界含量较多,位错密度较高.通过对三火次后的锻坯进行合适的热处理,Ⅰ区"项链"组织得到细化,Ⅱ、Ⅲ区组织发生晶粒长大,整个盘坯为较均匀的细晶组织,平均晶粒尺寸为6～8μm.
Nickel-base powder metallurgy( PM) superalloys are widely used as high temperature components in gas turbine engines owing to their outstanding mechanical properties and workability under intense heat. In order to meet the performance requirements of a new generation aircraft engine with a higher thrust-weight ratio,the fourth generation PM superalloy has been studied at home and abroad. Its operating temperature has been raised to 815-850 ℃. The alloy in this study was a newly-designed fourth generation PM superalloy,which exhibited excellent high temperature stress rupture and creep properties compared with the previous three generations' PM superalloys,FGH4095,FGH4096,and FGH4098. Based on the performance characteristics of PM superalloys of different grain sizes,dual microstructure heat treatment( DMHT) has been used to produce a turbine disk which has a fine-grained bore and a coarse-grained rim. Therefore,it was first necessary to obtain a uniform fine-grained disk. It has been demonstrated that the finegrained disk can be gained through hot isostatic pressing( HIP) and multi-steps of high temperature working. In order to study the influence of multiple isothermal forging( ITF) on the grain refinement of the advanced PM superalloy,three steps of ITF were employed;each deformation was about 40%. The effective strain distribution of the alloy during ITF was simulated by using the commercial finite element software DEFORM 2 D. Microstructures of those forgings were investigated by means of the electron back scattered diffraction( EBSD) technique. The experimental results show that during ITF,the axial section of the forging is divided into three regions. Region Ⅰ,located in the upper and lower end faces,has the smallest deformation. Region Ⅱ is located at both sides of the section,and its deformation is larger than that of region Ⅰ. And region Ⅲ,located in the center of the section,obtains the maximal deformation.After three steps of ITF,Regions Ⅱ and Ⅲ of the forging are fully recrystallized,and equiaxed fine-grained microstructures with an average grain size of 2-3 μm are generated. Nevertheless,necklace structures form near Region Ⅰ of the forging. A great amount of fine recrystallized grains distribute around the non-equiaxed deformed grains. The deformed grains contain plenty of low-angle grain boundaries( LAGBs),which mean that the dislocation density is very high. Through proper heat treatment,the necklace structure in RegionⅠ is refined. Meanwhile,grain growth occurs in Region Ⅱ and Ⅲ. These findings suggest that fine-grained disks with uniform microstructures can be achieved,and the average grain size is 6-8 μm.
Nickel-base powder metallurgy( PM) superalloys are widely used as high temperature components in gas turbine engines owing to their outstanding mechanical properties and workability under intense heat. In order to meet the performance requirements of a new generation aircraft engine with a higher thrust-weight ratio,the fourth generation PM superalloy has been studied at home and abroad. Its operating temperature has been raised to 815-850 ℃. The alloy in this study was a newly-designed fourth generation PM superalloy,which exhibited excellent high temperature stress rupture and creep properties compared with the previous three generations' PM superalloys,FGH4095,FGH4096,and FGH4098. Based on the performance characteristics of PM superalloys of different grain sizes,dual microstructure heat treatment( DMHT) has been used to produce a turbine disk which has a fine-grained bore and a coarse-grained rim. Therefore,it was first necessary to obtain a uniform fine-grained disk. It has been demonstrated that the finegrained disk can be gained through hot isostatic pressing( HIP) and multi-steps of high temperature working. In order to study the influence of multiple isothermal forging( ITF) on the grain refinement of the advanced PM superalloy,three steps of ITF were employed;each deformation was about 40%. The effective strain distribution of the alloy during ITF was simulated by using the commercial finite element software DEFORM 2 D. Microstructures of those forgings were investigated by means of the electron back scattered diffraction( EBSD) technique. The experimental results show that during ITF,the axial section of the forging is divided into three regions. Region Ⅰ,located in the upper and lower end faces,has the smallest deformation. Region Ⅱ is located at both sides of the section,and its deformation is larger than that of region Ⅰ. And region Ⅲ,located in the center of the section,obtains the maximal deformation.After three steps of ITF,Regions Ⅱ and Ⅲ of the forging are fully recrystallized,and equiaxed fine-grained microstructures with an average grain size of 2-3 μm are generated. Nevertheless,necklace structures form near Region Ⅰ of the forging. A great amount of fine recrystallized grains distribute around the non-equiaxed deformed grains. The deformed grains contain plenty of low-angle grain boundaries( LAGBs),which mean that the dislocation density is very high. Through proper heat treatment,the necklace structure in RegionⅠ is refined. Meanwhile,grain growth occurs in Region Ⅱ and Ⅲ. These findings suggest that fine-grained disks with uniform microstructures can be achieved,and the average grain size is 6-8 μm.
引文
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[3] Wu C J,Tao Y,Jia J. Microstructure and properties of an advanced nickel-base PM superalloy. J Iron Steel Res Int,2014,21(12):1152
[4] Reynolds P L. Superalloy Compositions,Articles,and Methods of Manufacture:US Patent,8147749. 2012--04--03
[5] Powell A,Bain K,Wessman A,et al. Advanced supersolvus nickel powder disk alloy DOE:chemistry,properties,phase formations and thermal stability//Superalloys 2016:Proceedings of the 13th Intenational Symposium of Superalloys. Hoboken,2016:189
[6] Mourer D P,Raymond E,Ganesh S,et al. Dual alloy disk development//Superalloys 1996. Warrendale,1996:637
[7] Gayda J. Dual microstructure heat treatment of a nickel-base disk alloy[J/OL]. NASA Technical Reports Server(2001-11--01)[2018--12-26]. https://ntrs. nasa. gov/search. jsp? R=20020013802
[8] Gayda J,Gabb T P,Kantzos P T. The effect of dual microstructure heat treatment on an advanced nickel-base disk alloy//Superalloys 2004. Warrendale,2004:323
[9] Tao Y,Zhang G X,Liu J T. Study on design of the device for thermal gradient heat-treatment process of PM superalloy disks. J Iron Steel Res,2011,23(Suppl 2):486(陶宇,张国星,刘建涛.粉末涡轮盘温度梯度热处理工装设计研究.钢铁研究学报,2011,23(增刊2):486)
[10] Tao Y,Jia J,Liu J T,et al. Preparation Method of Ultra-Fine Grain Nickel Based Superalloy:China Patent,CN102392147A.2012--03--28(陶宇,贾建,刘建涛,等.超细晶镍基粉末高温合金的制备方法:中国专利,CN102392147A. 2012-03-28)
[11] Liu Y,Tao Y,Jia J. The microstructure evolution of FGH98 P/M superalloy after hot deformation. Powder Metall Ind,2011,21(2):14(刘洋,陶宇,贾建. FGH98粉末冶金高温合金热变形过程中组织变化.粉末冶金工业,2011,21(2):14)
[12] Ning Y Q,Yao Z K,Wu Z,et al. The effects of repeated firing forging on microstructure and mechanical properties of GH4133A alloys. J Plast Eng,2008,15(4):98(宁永权,姚泽坤,吴泽,等.多火次锻造对GH4133A合金组织和性能的影响.塑性工程学报,2008,15(4):98)
[13] Ning Y Q,Yao Z K. Recrystallization nucleation mechanism of FGH4096 powder metallurgy superalloy. Acta Metall Sinica,2012,42(8):1005(宁永权,姚泽坤. FGH4096粉末高温合金的再结晶形核机制.金属学报,2012,48(8):1005)
[14] Xie X H,Yao Z K,Ning Y Q,et al. Dynamic recrystallization and grain refining of superalloy FGH4096. J Aeron Mater,2011,31(1):20(谢兴华,姚泽坤,宁永权,等. FGH4096合金的动态再结晶与晶粒细化研究.航空材料学报,2011,31(1):20)
[15] He G A,Liu F,Huang L,et al. Microstructure evolutions and nucleation mechanisms of dynamic recrystallization of a powder metallurgy Ni-based superalloy during hot compression. Mater Sci Eng A,2016,677:496
[16] Zhang B J,Zhao G P,Jiao L Y,et al. Influence of hot working process on microstructures of superalloy GH4586. Acta Metall Sinica,2005,41(4):351(张北江,赵光普,焦兰英,等.热加工工艺对GH4586合金微观组织的影响.金属学报,2005,41(4):351)
[2] Wu C J,Tao Y,Jia J. Study on composition variation range of the fourth generation PM superalloys. Powder Metall Ind,2014,24(1):20(吴超杰,陶宇,贾建.第四代粉末高温合金成分选取范围研究.粉末冶金工业,2014,24(1):20)
[3] Wu C J,Tao Y,Jia J. Microstructure and properties of an advanced nickel-base PM superalloy. J Iron Steel Res Int,2014,21(12):1152
[4] Reynolds P L. Superalloy Compositions,Articles,and Methods of Manufacture:US Patent,8147749. 2012--04--03
[5] Powell A,Bain K,Wessman A,et al. Advanced supersolvus nickel powder disk alloy DOE:chemistry,properties,phase formations and thermal stability//Superalloys 2016:Proceedings of the 13th Intenational Symposium of Superalloys. Hoboken,2016:189
[6] Mourer D P,Raymond E,Ganesh S,et al. Dual alloy disk development//Superalloys 1996. Warrendale,1996:637
[7] Gayda J. Dual microstructure heat treatment of a nickel-base disk alloy[J/OL]. NASA Technical Reports Server(2001-11--01)[2018--12-26]. https://ntrs. nasa. gov/search. jsp? R=20020013802
[8] Gayda J,Gabb T P,Kantzos P T. The effect of dual microstructure heat treatment on an advanced nickel-base disk alloy//Superalloys 2004. Warrendale,2004:323
[9] Tao Y,Zhang G X,Liu J T. Study on design of the device for thermal gradient heat-treatment process of PM superalloy disks. J Iron Steel Res,2011,23(Suppl 2):486(陶宇,张国星,刘建涛.粉末涡轮盘温度梯度热处理工装设计研究.钢铁研究学报,2011,23(增刊2):486)
[10] Tao Y,Jia J,Liu J T,et al. Preparation Method of Ultra-Fine Grain Nickel Based Superalloy:China Patent,CN102392147A.2012--03--28(陶宇,贾建,刘建涛,等.超细晶镍基粉末高温合金的制备方法:中国专利,CN102392147A. 2012-03-28)
[11] Liu Y,Tao Y,Jia J. The microstructure evolution of FGH98 P/M superalloy after hot deformation. Powder Metall Ind,2011,21(2):14(刘洋,陶宇,贾建. FGH98粉末冶金高温合金热变形过程中组织变化.粉末冶金工业,2011,21(2):14)
[12] Ning Y Q,Yao Z K,Wu Z,et al. The effects of repeated firing forging on microstructure and mechanical properties of GH4133A alloys. J Plast Eng,2008,15(4):98(宁永权,姚泽坤,吴泽,等.多火次锻造对GH4133A合金组织和性能的影响.塑性工程学报,2008,15(4):98)
[13] Ning Y Q,Yao Z K. Recrystallization nucleation mechanism of FGH4096 powder metallurgy superalloy. Acta Metall Sinica,2012,42(8):1005(宁永权,姚泽坤. FGH4096粉末高温合金的再结晶形核机制.金属学报,2012,48(8):1005)
[14] Xie X H,Yao Z K,Ning Y Q,et al. Dynamic recrystallization and grain refining of superalloy FGH4096. J Aeron Mater,2011,31(1):20(谢兴华,姚泽坤,宁永权,等. FGH4096合金的动态再结晶与晶粒细化研究.航空材料学报,2011,31(1):20)
[15] He G A,Liu F,Huang L,et al. Microstructure evolutions and nucleation mechanisms of dynamic recrystallization of a powder metallurgy Ni-based superalloy during hot compression. Mater Sci Eng A,2016,677:496
[16] Zhang B J,Zhao G P,Jiao L Y,et al. Influence of hot working process on microstructures of superalloy GH4586. Acta Metall Sinica,2005,41(4):351(张北江,赵光普,焦兰英,等.热加工工艺对GH4586合金微观组织的影响.金属学报,2005,41(4):351)