Mg-14.61Gd合金的定向凝固组织及生长取向
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摘要
采用电子背散射衍射(EBSD)和元胞自动机有限元(CAFE)方法研究了Mg-14.61Gd合金在温度梯度G=30 K/mm和抽拉速率v=10～200μm/s条件下的定向凝固组织和生长取向。研究发现,Mg-14.61Gd合金纵向凝固组织呈单一方向的α-Mg枝晶生长形貌,随着v的增加,枝晶界面生长方式由凸前生长向平齐生长转变,枝晶间距减小。当v从10μm/s增至100μm/s时,α-Mg枝晶的生长取向由<1120>和<1010>转变为<1120>,其与凝固热流的偏离角(θ)由11.0°减小至5.7°,热流是影响生长取向的主导因素;当v从100μm/s增至200μm/s时,α-Mg枝晶的生长取向仍为<1120>,但θ却逐渐增大至10.6°,此时,晶体的各向异性占主导。研究表明,CAFE模型可以合理预测定向凝固镁合金的晶粒组织和生长取向。
As one of the most promising heat-resistant magnesium alloys, Mg-Gd series alloy has a wide application prospect in the industrial fields of aerospace, cars, and rail transit. There have been extensive researches on the performance improvement of Mg-Gd series alloys. As known, dendrites are the common solidification microstructures of castings of magnesium alloys, and solidification conditions have a significant effect on dendrite morphologies and growth orientation, which could strongly affect the mechanical properties of castings, thus it is critical to study the grain growth regularity for predicting the performance of magnesium castings. However, there are few studies on numerical simulation of dendrite growth process and growth orientation of magnesium alloys. Solidification behavior of magnesium alloys can be scientifically studied via directional solidification technology, and cellular automaton finite element(CAFE) method should be effective to simulate the dendrite growth process of magnesium alloys. In present work, microstructures and growth orientation of directionally solidified Mg-14.61 Gd alloy under the temperature gradient G=30 K/mm and the withdrawal rate v=10～200 mm/s were investigated by EBSD measurement method and CAFE numerical simulation method. It was found that α-Mg primary phase presented unidirectional dendritic morphologies on longitudinal cross-section. The growth interface appearance of α-Mg changed from the protruding forward growth to the flat growth gradually and the dendritic arm spacing decreased gradually with the increasing v. when v increased from 10 mm/s to 100 mm/s, the main growth orientation of α-Mg changed from <1120> and <1010> to <1120>, and the deviation angle(θ) from solidification heat flow direction reduced from 11.0° to 5.7°, the reason for this lied mainly in the change of the heat flux. Further increasing v up to 200 mm/s, the main growth direction of α-Mg was still in <1120>, but the value of θ increased to 10.6°, and the anisotropy of the crystal was the dominant factor then. It was proved that the CAFE numerical simulation model could predict the grain structure and growth orientation reasonably for Mg alloy.
As one of the most promising heat-resistant magnesium alloys, Mg-Gd series alloy has a wide application prospect in the industrial fields of aerospace, cars, and rail transit. There have been extensive researches on the performance improvement of Mg-Gd series alloys. As known, dendrites are the common solidification microstructures of castings of magnesium alloys, and solidification conditions have a significant effect on dendrite morphologies and growth orientation, which could strongly affect the mechanical properties of castings, thus it is critical to study the grain growth regularity for predicting the performance of magnesium castings. However, there are few studies on numerical simulation of dendrite growth process and growth orientation of magnesium alloys. Solidification behavior of magnesium alloys can be scientifically studied via directional solidification technology, and cellular automaton finite element(CAFE) method should be effective to simulate the dendrite growth process of magnesium alloys. In present work, microstructures and growth orientation of directionally solidified Mg-14.61 Gd alloy under the temperature gradient G=30 K/mm and the withdrawal rate v=10～200 mm/s were investigated by EBSD measurement method and CAFE numerical simulation method. It was found that α-Mg primary phase presented unidirectional dendritic morphologies on longitudinal cross-section. The growth interface appearance of α-Mg changed from the protruding forward growth to the flat growth gradually and the dendritic arm spacing decreased gradually with the increasing v. when v increased from 10 mm/s to 100 mm/s, the main growth orientation of α-Mg changed from <1120> and <1010> to <1120>, and the deviation angle(θ) from solidification heat flow direction reduced from 11.0° to 5.7°, the reason for this lied mainly in the change of the heat flux. Further increasing v up to 200 mm/s, the main growth direction of α-Mg was still in <1120>, but the value of θ increased to 10.6°, and the anisotropy of the crystal was the dominant factor then. It was proved that the CAFE numerical simulation model could predict the grain structure and growth orientation reasonably for Mg alloy.
引文
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[21]Liu S J,Yang G Y,Jie W Q.Microstructure,microsegregation,and mechanical properties of directional solidified Mg-3.0Nd-1.5Gd Alloy[J].Acta Metall.Sin.(Engl.Lett.),2014,27:1134
[22]Matache G,Stefanescu D M,Puscasu C,et al.Investigation of solidification microstructure of single crystal CMSX-4 superalloyExperimental measurements and modelling predictions[J].Int.J.Cast Met.Res.,2015,28:323
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[26]Wang J H,Yang G Y,Liu S J,et al.Microstructure and room temperature mechanical properties of directionally solidified Mg-2.35Gd magnesium alloy[J].Trans.Nonferrous Met.Soc.China,2016,26:1294
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[29]Gandin C A,Rappaz M,Tintillier R.3-Dimensional simulation of the grain formation in investment castings[J].Metall.Mater.Trans.,1994,25A:629
[30]Wang Y N,Huang J C.Texture analysis in hexagonal materials[J].Mater.Chem.Phys.,2003,81:11
[31]Wang J A,Shi Y,Zhang J W.Microstructure and micro segregation of Mg-1.5Gd alloy under directional solidification station[J].Heat Treat.Met.,2015,40(7):115(王甲安,石岩,张锦文.定向凝固下Mg-1.5Gd合金的微观结构与微观偏析[J].金属热处理,2015,40(7):115)
[32]Peng Q M,Ma N,Li H.Gadolinium solubility and precipitate identification in Mg-Gd binary alloy[J].J.Rare Earth,2012,30:1064
[33]Pettersen K,Lohne O,Ryum N.Dendritic solidification of magnesium alloy AZ91[J].Metall.Trans.,1990,21A:221
[34]Bei H,George E P,Kenik E A,et al.Directional solidification and microstructures of near-eutectic Cr-Cr3Si alloys[J].Acta Mater.,2003,51:6241
[35]Luo S F,Yang G Y,Liu S J,et al.Microstructure evolution and mechanical properties of directionally solidified Mg-x Gd(x=0.8,1.5,and 2.5)alloys[J].Mater.Sci.Eng.,2016,A662:241
[36]Xiao Z X,Zheng L J,Yang L L,et al.Effects of temperature gradient on lamellar orientations of directional solidified TiAl-based alloy[J].Acta Matell.Sin.,2010,46:1223(肖志霞,郑立静,杨莉莉等.温度梯度对定向凝固TiAl基合金片层取向的影响[J].金属学报,2010,46:1223)
[2]Gao L,Chen R S,Han E H.Effects of rare-earth elements Gd and Yon the solid solution strengthening of Mg alloys[J].J.Alloys Compd.,2009,481:379
[3]Jie Y,Wang L D,Wang L M,et al.Microstructures and mechanical properties of the Mg-4.5Zn-x Gd(x=0,2,3 and 5)alloys[J].J.Alloys Compd.,2008,459:274
[4]Zheng X W,Luo A A,Zhang C,et al.Directional solidification and microsegregation in a magnesium-aluminum-calcium alloy[J].Metall.Mater.Trans.,2012,43A:3239
[5]Asta M,Beckermann C,Karma A,et al.Solidification microstructures and solid-state parallels:Recent developments,future directions[J].Acta Mater.,2009,57:941
[6]Zou M Q,Huang C Q,Xia W J,et al.Study on the crystal orientations and mechanical properties of AZ31 magnesium alloy produced by directional solidification[J].Foundry,2006,55:890(邹敏强,黄长清,夏伟军等.定向凝固AZ31镁合金晶粒取向及力学性能研究[J].铸造,2006,55:890)
[7]Pettersen K,Ryum N.Crystallography of directionally solidified magnesium alloy AZ91[J].Metall.Trans.,1989,20A:847
[8]Jing T,Shuai S S,Wang M Y,et al.Research progress on 3D dendrite morphology and orientation selection during the solidification of Mg alloys:3D experimental characterization and phase field modeling[J].Acta Matell.Sin.,2016,52:1279(荆涛,帅三三,汪明月等.镁合金凝固过程三维枝晶形貌和生长取向研究进展:三维实验表征和相场模拟[J].金属学报,2016,52:1279
[9]Wang M Y,Xu Y J,Jing T,et al.Growth orientations and morphologies of a-Mg dendrites in Mg-Zn alloys[J].Scr.Mater.,2012,67:629
[10]Yang X L,Dong H B,Wang W,et al.Microscale simulation of stray grain formation in investment cast turbine blades[J].Mater.Sci.Eng.,2004,A386:129
[11]Ramirez A,Carrillo F,Gonzalez J L,et al.Stochastic simulation of grain growth during continuous casting[J].Mater.Sci.Eng.2006,A421:208
[12]Rappaz M,Gandin C A.Probabilistic modelling of microstructure formation in solidification processes[J].Acta Metall.Mater.,1993,41:345
[13]Gandin C A,Rappaz M.A coupled finite element-cellular automaton model for the prediction of dendritic grain structures in solidification processes[J].Acta Metall.Mater.,1994,42:2233
[14]Kermanpur A,Mehrara M,Varahram N,et al.Improvement of grain structure and mechanical properties of a land based gas turbine blade directionally solidified with liquid metal cooling process[J].Mater.Sci.Technol.,2008,24:100
[15]Takatani H,Gandin C A,Rappaz M.EBSD characterisation and modelling of columnar dendritic grains growing in the presence of fluid flow[J].Acta Mater.,2000,48:675
[16]Carozzani T,Digonnet H,Gandin C.3D CAFE modeling of grain structures:Application to primary dendritic and secondary eutectic solidification[J].Modell.Simul.Mater.Sci.Eng.,2012,20:15010
[17]Wang M Y,Williams J J,Jiang L,et al.Dendritic morphology of aMg during the solidification of Mg-based alloys:3D experimental characterization by X-ray synchrotron tomography and phase-field simulations[J].Scr.Mater.,2011,65:855
[18]B?ttger B,Eiken J,Ohno M,et al.Controlling microstructure in magnesium alloys:A combined thermodynamic,experimental and simulation approach[J].Adv.Eng.Mater.,2006,8:241
[19]Yuan X F,Ding Y T,Guo T B,et al.Numerical simulation of dendritic growth of magnesium alloys using phase-field method under forced flow[J].Chin.J.Nonferrous Met.,2010,20:1474(袁训锋,丁雨田,郭廷彪等.强制对流作用下镁合金枝晶生长的相场法数值模拟[J].中国有色金属学报,2010,20:1474)
[20]Liu Z Y,Xu Q Y,Liu B C.Modeling of dendrite growth for the cast magnesium alloy[J].Acta Matell.Sin.,2007,43:367(刘志勇,许庆彦,柳百成.铸造镁合金的枝晶生长模拟[J].金属学报,2007,43:367)
[21]Liu S J,Yang G Y,Jie W Q.Microstructure,microsegregation,and mechanical properties of directional solidified Mg-3.0Nd-1.5Gd Alloy[J].Acta Metall.Sin.(Engl.Lett.),2014,27:1134
[22]Matache G,Stefanescu D M,Puscasu C,et al.Investigation of solidification microstructure of single crystal CMSX-4 superalloyExperimental measurements and modelling predictions[J].Int.J.Cast Met.Res.,2015,28:323
[23]ESI Software Inc.PROCAST User's Manual and Technical Reference.Version 3.1.1,2008
[24]Elliott A J,Pollock T M.Thermal analysis of the Bridgman and liquid-metal-cooled directional solidification investment casting processes[J].Metall.Mater.Trans.,2007,38A:871
[25]Pang R P,Wang F M,Zhang G Q,et al.Study of solidification thermal parameters of 430 ferrite stainless steel based on 3D-CAFE method[J].Acta Metall.Sin.,2013,49:1234(庞瑞朋,王福明,张国庆等.基于3D-CAFE法对430铁素体不锈钢凝固热参数的研究[J].金属学报,2013,49:1234)
[26]Wang J H,Yang G Y,Liu S J,et al.Microstructure and room temperature mechanical properties of directionally solidified Mg-2.35Gd magnesium alloy[J].Trans.Nonferrous Met.Soc.China,2016,26:1294
[27]Ma J,Wang B,Zhao S L,et al.Incorporating an extended dendritic growth model into the CAFE model for rapidly solidified nondilute alloys[J].J.Alloys Compd.,2016,668:46
[28]Kurz W,Giovanola B,Trivedi R.Theory of microstructural development during rapid solidification[J].Acta Metall.,1986,34:823
[29]Gandin C A,Rappaz M,Tintillier R.3-Dimensional simulation of the grain formation in investment castings[J].Metall.Mater.Trans.,1994,25A:629
[30]Wang Y N,Huang J C.Texture analysis in hexagonal materials[J].Mater.Chem.Phys.,2003,81:11
[31]Wang J A,Shi Y,Zhang J W.Microstructure and micro segregation of Mg-1.5Gd alloy under directional solidification station[J].Heat Treat.Met.,2015,40(7):115(王甲安,石岩,张锦文.定向凝固下Mg-1.5Gd合金的微观结构与微观偏析[J].金属热处理,2015,40(7):115)
[32]Peng Q M,Ma N,Li H.Gadolinium solubility and precipitate identification in Mg-Gd binary alloy[J].J.Rare Earth,2012,30:1064
[33]Pettersen K,Lohne O,Ryum N.Dendritic solidification of magnesium alloy AZ91[J].Metall.Trans.,1990,21A:221
[34]Bei H,George E P,Kenik E A,et al.Directional solidification and microstructures of near-eutectic Cr-Cr3Si alloys[J].Acta Mater.,2003,51:6241
[35]Luo S F,Yang G Y,Liu S J,et al.Microstructure evolution and mechanical properties of directionally solidified Mg-x Gd(x=0.8,1.5,and 2.5)alloys[J].Mater.Sci.Eng.,2016,A662:241
[36]Xiao Z X,Zheng L J,Yang L L,et al.Effects of temperature gradient on lamellar orientations of directional solidified TiAl-based alloy[J].Acta Matell.Sin.,2010,46:1223(肖志霞,郑立静,杨莉莉等.温度梯度对定向凝固TiAl基合金片层取向的影响[J].金属学报,2010,46:1223)