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采用基于密度泛函理论的第一性原理方法，计算研究了La替位Ti或Al且掺杂浓度分别为1.85 at.%，2.78 at.%，4.17 at.%，6.25 at.%，8.33 at.%，12.5 at.%的-TiAl合金的晶体结构、稳定性和延性等性质.结果显示，杂质La浓度x12.5 at.%，各个体系均具有较好的能量稳定性，即在一定条件下它们是可以实验制备的，且掺杂合金体系的密度4.6 gcm-3.La掺杂引起晶格参量变化进而导致合金体系的轴比发生变化.La的低浓度（x6.25 at.%）掺杂使合金体系的轴比相较纯-TiAl更接近于1，这对于改善材料的延性极为有利，其中Ti11LaAl12体系的轴比最接近于1，预报其延性最佳.通过对比Ti11LaAl12和Ti12Al12体系的布居数、电荷密度和电子态密度，发现Ti11LaAl12体系延性改善的电子因素为：掺杂使体系内Al（Ti）原子轨道上的电子重新分布，Ti-d轨道和Al-p轨道的电子数均减小，可被p-d杂化轨道局域化的电子数减小，p-d轨道杂化键强度降低，从而使位错移动的阻力减少，延性得以明显改善.电子重新分布改变了部分化学键的性质，部分AlTi共价键转化为AlLa离子键，部分TiTi共价键转化为TiLa金属键，它们的共价性及方向性明显降低，材料金属性增强.在掺杂体系中AlAl键的平均强度减弱，AlTi键和TiTi键的平均强度增强，三者的强度差异明显减小，晶体结构的各向异性程度降低.Because of the low density, high specific strength and excellent performance at high temperature, -TiAl based alloy has become a new generation of materials in the aeronautic field. However, its poor ductility at room temperature set a limitation to its wide applications. In this paper, the crystal structures, stabilities and ductilities of La-doped -TiAl systems are investigated by using first principles method based on density functional theory, in which Ti or Al is substituted by La and the impurity content values are 1.85 at.%, 2.78 at.%, 4.17 at.%, 6.25 at.%, 8.33 at.% and 12.5 at.%, respectively. The results show that all of the La-doped alloys have good energy stabilities, namely they can be prepared experimentally, when the impurity concentration x of system is less than or equal to 12.5 at.%. And the density of the La-doped system is less than 4.6 gcm-3. La doping induces the lattice parameters and the axial ratio of the alloy system to change. The axial ratio of La-doped system with low impurity concentration (x6.25 at.%) is closer to 1, which is very beneficial to improving the ductility of the materials. It is predicted that the system Ti11LaAl12 would have the best ductility among those of the investigated systems, for its axial ratio is the closest to 1. The electronic effect about the ductility of La-doped system is discussed through the comparisons of the populations, charge densities and densities between the states of systems Ti11LaAl12 and Ti12Al12. It is found that the system Ti11LaAl12 presents a state of electron redistribution in valence electron orbitals of Al and Ti due to an atom of titanium substituted with that of lanthanum. The charge numbers of Ti-d and Al-p orbitals and the numbers of electrons can be delocalized by reducing the p-d orbital hybridization. Thus, the intensity of p-d orbital hybridization is weakened, the resistance of dislocation movement is reduced, and the ductility of TiAl systems can be improved. Actually, the new electron redistribution shows different properties of some chemical bonds, in which some of covalent AlTi bonds are replaced by ionic AlLa bonds and some of covalent TiTi bonds are replaced by metallic TiLa bonds. Therefore, the covalent and directional properties of chemical bonds are reduced distinctly while the metallic properties of materials are strengthened. The average intensity of AlAl bonds decreases and those of AlTi and TiTi bonds are increased in the La-doped -TiAl system (Ti11LaAl12). As a result, the differences between the three kinds of chemical bonds diminish and the degree of isotropy of the crystal structure increases, which can greatly improve the ductility of -TiAl alloy.
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Keywords:
- La-doped -TiAl /
- crystal structure /
- ductility /
- electronic property
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[2] Bewlay B P, Nag S, Suzuki A, Weimer M J 2016 Mater. High Temp. 33 549
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[28] Pugh S F 1954 Philos. Mag. 45 823
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[31] Dang H L, Wang C Y, Yu T 2007 Acta Phys. Sin. 56 2838 (in Chinese) [党宏丽, 王崇愚, 于涛 2007 56 2838]
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[1] Castillo-Rodriguez M, No M L, Jimenez J A, Ruano O A, Juan J S 2016 Acta Mater. 103 46
[2] Bewlay B P, Nag S, Suzuki A, Weimer M J 2016 Mater. High Temp. 33 549
[3] Qian J H, Qi X Z 2002 Chin. J. Rare Metal. 26 477 (in Chinese) [钱九红, 祁学忠 2002 稀有金属 26 477]
[4] Pollock T M 2016 Nat. Mater. 15 809
[5] Kawabta T, Tamura T, Izumi O 1993 Metall. Trans. A 24 141
[6] Song Q G, Qin G S, Yang B B, Jiang Q J, Hu X L 2016 Acta Phys. Sin. 65 046102 (in Chinese) [宋庆功, 秦国顺, 杨宝宝, 蒋清杰, 胡雪兰 2016 65 046102]
[7] Yamaguchi M, Ito K 2000 Acta Mater. 48 307
[8] Kawabata T, Izumi O 1987 Philos. Mag. A 55 823
[9] Huang S C, Hall E L 1991 Acta Metall. Mater. 39 1053
[10] Pu Z J, Shi J D, Zou D S, Zhong Z Y 1993 Acta Metall. Sin. 29 31 (in Chinese) [蒲忠杰, 石建东, 邹敦叙, 仲增墉 1993 金属学报 29 31]
[11] 10+ Chen G, Peng Y B, Zheng G, Qi Z X, Wang M Z, Yu H C, Dong C L, Liu C T 2016 Nat. Mater. 15 876
[12] Kawabata T, Takezono Y, Kanai T, O Izumi 1988 Acta Metall. Mater. 36 963
[13] Song X P, Chen G L 2002 Acta Metall. Sin. 38 583 (in Chinese) [宋西平, 陈国良 2002 金属学报 38 583]
[14] Yang R 2015 Acta Metall. Sin. 51 129 (in Chinese) [杨锐 2015 金属学报 51 129]
[15] Hu H, Wu X Z, Wang R, Li W G, Liu Q 2016 J. Alloys Compd. 658 689
[16] Yang Z J, Sun H L, Huang Z W, Zhu D G, Wang L H 2015 Mater. Rev.: Rev. 29 85 (in Chinese) [杨镇骏, 孙红亮, 黄泽文, 朱德贵, 王良辉 2015 材料导报:综述篇 29 85]
[17] Xu F S, Geng H R, Wang S R 2009 Rare Metal. Mat. Eng. 38 361 (in Chinese) [徐福松, 耿浩然, 王守仁 2009 稀有金属材料与工程 38 361]
[18] Hadi M, Meratian M, Shafyei A 2015 J. Alloys Compd. 618 27
[19] Chen S Q, Qu X H, Lei C M, Huang B Y 1994 Acta Metall. Sin. 30 20 (in Chinese) [陈仕奇, 曲选辉, 雷长明, 黄伯云 1994 金属学报 30 20]
[20] Greenberg B A, Antonov O V, Indenbaum V N, Karkin L E, Notkin A B, Ponomarev M V, Smirnov L V 1991 Acta Metall. Mater. 39 233
[21] Morinaga M, Saito J, Yukawa N, Adachi H 1990 Acta Metall. Mater. 38 25
[22] Eberhart M E, Clougherty D P, Maclaren J M 1993 Philos. Mag. B 68 455
[23] Qin Y H, Qiao Y J 2015 J. Harbin Inst. Technol. 47 123 (in Chinese) [秦永和, 乔英杰 2015 哈尔滨工业大学学报 47 123]
[24] Paul R, Katherine C E, Philip D F A, Casey F, Malia B W, Aurelio M, Matthias Z, Sorelle A F, Joshua S, Alexander J N 2016 Nature 533 73
[25] Song Q G 2004 Chin. Sci. Bull. 49 210
[26] Chen G L, Lin J P 1999 Physicalmetallurgy Basis of Ordered Intermetallic Compound Structure Materials (Beijing: Metallurgical Industry Press) p285 (in Chinese) [陈国良, 林均品 1999 有序金属间化合物结构材料物理金属学基础 (北京: 冶金工业出版社) 第285页]
[27] Shang J X, Yu T B 2009 Acta Phys. Sin. 58 1179 (in Chinese) [尚家香, 于潭波 2009 58 1179]
[28] Pugh S F 1954 Philos. Mag. 45 823
[29] Fu C L 1990 J. Mater. Res. 5 971
[30] Huang Y Y, Wu W M, Deng W, Zhong X P, Xiong L Y, Cao M Z, Long Q W 2000 Chin. J. Nonferr. Met. 10 796 (in Chinese) [黄宇阳, 吴伟明, 邓文, 钟夏平, 熊良钺, 曹名洲, 龙期威 2000 中国有色金属学报 10 796]
[31] Dang H L, Wang C Y, Yu T 2007 Acta Phys. Sin. 56 2838 (in Chinese) [党宏丽, 王崇愚, 于涛 2007 56 2838]
[32] Liu X K, Liu Y, Zheng Z, Dai J L 2010 Rare Metal. Mat. Eng. 39 832 (in Chinese) [刘显坤, 刘颖, 郑州, 代君龙 2010 稀有金属材料与工程 39 832]
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