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Acta Metall Sin  2019, Vol. 55 Issue (2): 291-298    DOI: 10.11900/0412.1961.2018.00182
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Molecular Dynamics Simulation of the Structure and Deformation Behavior of γ/α2 Interface in TiAl Alloys
Aidong TU1,2, Chunyu TENG3, Hao WANG1(), Dongsheng XU1, Yun FU3, Zhanyong REN3, Rui YANG1
1 Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
2 School of Materials Science and Engineering, University of Science and Technology of China, Shenyang 110016, China
3 Laboratory of Fundamental Research, AVIC China Aero-Polytechnology Establishment, Beijing 100028, China
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TiAl alloys with γ-TiAl and α2-Ti3Al dual-phase lamellar structure possess not only excellent high temperature performance but also density only about half of traditional superalloys. Such lamellar structure largely determines the mechanical properties of TiAl alloys. However, there is still a lack of understanding on the atomic structure of lamella, as well as their influence on the mechanical behaviors. For this reason, molecular dynamics with an embedded-atom potential is employed to investigate the energies of both the coherent and semi-coherent γ/α2 interfaces. The interface coherency is found to depend on the thickness ratio of γ lamellae to α2 lamellae, and there exists a critical lamella thickness, below/above which the interface is coherent/semi-coherent. Tensile loading perpendicular to the lamella interface indicates that the yield strength of coherent interface is higher than that of semi-coherent interface and the crack nucleation behavior varies with the thickness ratio of γ lamellae to α2 lamellae. The plastic deformation occurs first in the γ region, forming Shockley partial dislocations and then crosses the γ/α2 interface via slip transfer, activating stacking faults on the pyramidal plane in the α2 region. In this process, the γ/α2 interface provides nucleation sites for subsequent dislocations and cracks.

Key words:  TiAl      interface      plastic deformation      mechanical behavior      molecular dynamics     
Received:  07 May 2018     
ZTFLH:  TG146.2  
Fund: Supported by National Key Research and Development Program of China (No.2016YFB0701304), National Natural Science Foundation of China (No.51671195), Aeronautical Science Foundation of China (No.20160292002), Youth Innovation Promotion Association of Chinese Academy of Sciences (No.2015151) and Special Project on Information Technology of Chinese Academy of Sciences (No.XXH13506-304)

Cite this article: 

Aidong TU, Chunyu TENG, Hao WANG, Dongsheng XU, Yun FU, Zhanyong REN, Rui YANG. Molecular Dynamics Simulation of the Structure and Deformation Behavior of γ/α2 Interface in TiAl Alloys. Acta Metall Sin, 2019, 55(2): 291-298.

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Fig.1  Projections of atoms close to the two coherent interfaces along [110]γ or [112?0]α2 (a1, b1), projections of the two atomic layers close to γ/α2 interface along [111]γ or [0001]α2 (a2, b2), and generalized stacking fault energy surface along the interface (c) (M—metastable, S—stable)
Fig.2  Top view of γ/α2 semi-coherent interface (a) and projection of the two atomic layers close to the γ/α2 interface along [111]γ or [0001]α2 of the boxed zone in Fig.2a (b)
Fig.3  Total energy against the lamellar thickness of γ and α2 (a) and the relationship between the total energy and the lamellar thickness of α2 (b)
Fig.4  Thompson tetrahedron and some important deformation vectors (a), emission of Shockley partial dislocations from coherent (b) and semi-coherent interfaces, respectively (c), and slip transfer across the interface from γ to α2 and pyramidal plane stacking fault activated in α2 (inset) (d)
Fig.5  Atomic configurations of coherent interface during tensile deformation when the thickness ratios of γ to α2 are 1∶1 (a1~a3) and 2∶1 (b1~b3), respectively
Fig.6  Atomic configurations of semi-coherent interface during tensile deformation when the thickness ratios of γ to α2 are 1∶1 (a1, a2) and 2∶1 (b1, b2), respectively
Fig.7  Tensile stress-strain curves of coherent (a) and semi-coherent (b) interfaces with different lamella thicknesses
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