1 School of Materials Science and Engineering, Central South University, Changsha 410083, China 2 Key Laboratory of Nonferrous Metal Materials Science and Engineering,Ministry of Education, Central South University, Changsha 410083, China 3 State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, China
Cite this article:
Huijin TAO,Shan ZHOU,Yu LIU,Jian YIN,Hao XU. Point Defect Concentrations and Interactions in D019-Ti3Al from First-Principles Calculations. Acta Metall Sin, 2017, 53(6): 751-759.
The intermetallics D019-Ti3Al has low specific density and high thermal resistance for both bulk and coating applications in engineering area. The point defects such as thermal vacancy, compostion vacancy and antisite defect have great influence on the properties of D019-Ti3Al, but are usally neglected. According to available research data from both theory and experiment, it is commonly considered that the thermal vacancies in D019-Ti3Al provide paths for atomic migration and diffusion, the antisite defects play an important role in the disordering of D019-Ti3Al, and the interaction between composition vacancy and antisite defect may have important influence on atomic diffusion and dislocation movement. So it is necessary to explore the mechanism of interaction between composition vacancy and antisite defect for more accurate understanding of the atomic diffusion, dislocation movement and plastic deform in D019-Ti3Al. In this work, the formation enthalpy, equilibrium concentration, and binding energy of composition vacancy and antisite defect in D019-Ti3Al intermetallics were calculated by using both the Wagner-Schottky model of point defect thermodynamics and the plane wave pseudopotential method in first-principles. Results suggest that, in the whole composition range of interest, the point defect concentrations increase with the increase of temperature. In particular, the concentrations of antisite defects are higher than those of vacancies, and the vacancy concentration of Ti is higher than that of Al. At the stoichiometric composition, the concentrations of antisite defects of Ti and Al are very close. At the Ti-rich side of component, the antisite defect of Ti dominates in concentration, while at the Al-rich side, that of Al dominates in concentration. For the calculated results of 3 types of point defect pairs, AlTi-TiAl, TiAl-TiAl and VAl-AlTi, they may have the strong trend to aggregate, while others may show the tend to diffuse into the matrix.
Fund: Supported by National Natural Science Foundation of China (Nos.51302322 and 21373273), Open-End Fund for the Valuable and Precision Instruments of Central South University (Nos.CSUZC201708 and CSUZC201613), Education Reform Project of Central South University (Nos.2016jy03 and 2016CLYJG02) and Open Foundation of Guangdong Provincial Key Laboratory for Technology and Application of Metal Toughening, Guangdong Institute of Materials and Processing (No.GKL201605)
Fig.1 Schematics of supercell models of D019-Ti3Al intermetallics (a) conventional cell (b) perfect supercell (c) supercell with Ti vacancy (d) supercell with Al vacancy (e) supercell with Ti antisite defect (f) supercell with Al antisite defect
Fig.2 Relations between formation enthalpy and atomic content of Al (xAl) in D019-Ti3Al with single point defect (VAl—Al vacancy, VTi—Ti vacancy, AlTi—antisite Al, TiAl—antisite Ti)
Work
HVAl
HVTi
HAlTi
HTiAl
Present work
3.4272
1.9719
-0.2093
1.2416
Cal.[19]
1.5
1.5
0.6
0.6
Cal.[29]
2.76
3.15
0.54
0.16
Exp.[30]
-
1.55
-
-
Table 1 Calculated formation enthalpies (H) of vacancies and antisite defects in D019-Ti3Al (eVatom-1)
Fig.3 Point defect concentrations vs composition (xAl) of D019-Ti3Al intermetallics at different temperatures (a) 873 K (b) 1073 K (c) 1273 K (d) 1473 K
Fig.4 Point defect concentration as a function of temperature in stoichiometric D019-Ti3Al
Fig.5 Point defect concentrations (c) as a function of temperature(T -1) in D019-Ti3Al intermetallics
Fig.6 Schematics of supercell model of the first (a), second (b) and third (c) nearest VAl-VTi point defect pair in D019-Ti3Al
Temperature
Q?VAl
Q?VTi
Q?AlTi
Q?TiAl
800~1500 K
1.489
0.762
0.511
0.511
800~1200 K
0.866
0.139
0.513
0.513
1200~1500 K
2.944
2.218
0.508
0.508
Cal.[18]
1.805
1.314
0.313
0.313
Exp.[18]
1.55
Table 2 Prediction of activation energy (Q?) of vacancy and antisite defects in D019-Ti3Al (eVatom-1)
Point defect pair
Hd-d' / eV
Fd-d' / eV
First nearest
Second nearest
Third nearest
First nearest
Second nearest
Third nearest
VAl-VTi
5.5203
5.5045
5.9087
-0.1212
-0.1054
-0.5096
VAl-AlTi
3.1869
3.3116
3.4959
0.0310
-0.0937
-0.2780
VTi-TiAl
3.6256
3.5722
3.5010
-0.4121
-0.3587
-0.2875
AlTi-TiAl
0.8544
1.0014
1.0454
0.1779
0.0309
-0.0131
VAl-TiAl
4.8687
4.7788
4.9194
-0.1999
-0.1100
-0.2506
VTi-AlTi
2.0442
2.1019
1.9564
-0.2816
-0.3393
-0.1938
VAl-VAl
7.4272
7.4542
7.5333
-0.5728
-0.5998
-0.6789
VTi-VTi
4.4483
4.4546
4.3857
-0.5045
-0.5108
-0.4419
AlTi-AlTi
-0.2922
-0.2903
-0.5427
-0.1264
-0.1283
0.1241
TiAl-TiAl
2.4479
2.5269
2.5390
0.0353
-0.0437
-0.0558
Table 3 Formation enthalpy (Hd-d') and binding energy (Fd-d') of the nearest point defect pairs in D019-Ti3Al
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