PLASTIC DEFORMATION BEHAVIOR OF DIRECTION-ALLY SOLIDIFIED U720Li ALLOY AT ELEVATEDTEMPERATURE
Bo GAO1,Lei WANG1(),Taosha LIANG1,Yang LIU1,Xiu SONG1,Jinglong QU2
1 Key Lab for Anisotropy and Texture of Materials, Ministry of Education, Northeastern University, Shenyang 110819, China 2 High Temperature Material Research Institute, Central Iron and Steel Research Institute, Beijing 100081, China
Cite this article:
Bo GAO,Lei WANG,Taosha LIANG,Yang LIU,Xiu SONG,Jinglong QU. PLASTIC DEFORMATION BEHAVIOR OF DIRECTION-ALLY SOLIDIFIED U720Li ALLOY AT ELEVATEDTEMPERATURE. Acta Metall Sin, 2016, 52(4): 437-444.
U720Li, a kind of precipitation type nickel-based superalloy, shows excellent mechanical properties at elevated temperature, which is also known as the difficult-to-deform alloy because of the high-alloying. To solve its deformation problem, new methods would be developed to enlarge the temperature deforming window and improve its plasticity. The hot compression deformation behaviors of directionally solidified and equiaxed grain U720Li alloys were studied by the MMS-300 testing system, as well as the dynamic recrystallization nucleation and growth mechanisms during the hot deformation were discussed. The microstructural characteristics of the alloy under different deformation conditions were examined using OM, SEM and EBSD. The results show that the deforming resistances of both directionally solidified and equiaxed grain U720Li alloys decrease with the increasing of deforming temperature. When the angle θ between the compression deforming direction and dendrite growth direction is 90°, the deforming resistance of directionally solidified U720Li alloy would be lower. With this direction, the coordination deformation between the dendrites becomes better and no crack can be found after deformation, which indicates that the deforming ability is best along θ=90° and it can be considered as the optimal deforming direction for directionally solidified U720Li alloy. Compared with equiaxed grain alloy, directionally solidified U720Li alloy performs higher deformation ability and more homogenous microstructures. During the deformation of directionally solidified U720Li alloy, bulging nucleation of grain boundary migration and dislocation pile-up induced nucleation are found as the main mechanism for the nucleation of dynamic recrystallization. In addition, the deformation activation energy of directionally solidified U720Li alloy is 766 kJ/mol, which is 482 kJ/mol lower than that of equiaxed grain alloy, indicating the directionally solidified U720Li alloy exhibits better hot-working plasticity.
Fund: Supported by National Natural Science Foundation of China (Nos.51171039 and 51371044) and High Technology Research and Development Program of China (No.2012AA-03A513)
Fig.1 OM images of as-cast dendrite in longitudinal section (a, d), γ+γ' (b, e) and block carbide (c, f) of directionally solidified (a~c) and equiaxed grain (d~f) U720Li alloy (Inset in Fig.1a shows cross section image)
Fig.2 True stress-true strain curves of directionally solidified U720Li alloy deformed at 1100 ℃ (a) and 1125 ℃ (b) with strain rate ε˙=0.1 s-1 (after correction)
Fig.3 Relationships between peak stress (σs) and θ at different temperatures of directionally solidified U720Li alloy during hot deformation (θ—angle between the compression deforming direction and dendrite growth direction)
Fig.4 OM images of directionally solidified U720Li alloy deformed from θ=0° (a) and θ=90° (b) (Arrows in Fig.4a show the pores and cracks)
Fig.5 Peak stresses-temperature relationship curves of U720Li alloy at different deformation conditions (DS—directional solidification, EG—equiaxed grain)
Fig.6 OM images of directionally solidified (a) and equiaxed grain (b) U720Li alloy deformed for 30% at 1125 ℃ and 1 s-1 (DRX—dynamic recrystallization)
Strain rate ε˙ / s-1
1025 ℃
1050 ℃
1075 ℃
1100 ℃
1125 ℃
1150 ℃
0.01
66.38
65.03
63.74*
62.50*
61.30*
60.14*
0.1
68.68
67.34*
66.05*
64.80*
63.60*
62.44*
1
70.98
69.64
68.35*
67.10*
65.90*
64.75*
Table 1 Values of lnZ in directionally solidified U720Li alloy 30% deformed at different temperatures and strain rates
Fig.7 OM images of directionally solidified U720Li alloy deformed for 30% at different deformation conditions
Fig.8 OM images of directionally solidified U720Li alloy deformed for 30% at 1075 ℃ and 0.1 s-1
Fig.9 SEM images of directionally solidified U720Li alloy deformed for 30% at 1125 ℃ and 0.1 s-1
Fig.10 EBSD analysis of the longitudinal section in directionally solidified U720Li alloy deformed for 30% at 1150 ℃ as well as 0.1 s-1 (a) and 0.005 s-1 (b)
[1]
Guo J T.Materials Science and Engineering for Superalloys. Vol.1, Beijing: Science Press, 2008: 3
[1]
(郭建亭. 高温合金材料学(上册). 北京: 科学出版社, 2008: 3)
[2]
Huang Q Y, Li H K.Superalloy. Beijing: Metallurgy Industry Press, 2000: 1
[2]
(黄乾尧, 李汉康. 高温合金. 北京:冶金工业出版社, 2000: 1)
[3]
Sharqhi-Moshtaqhin R, Asqari S.J Mater Process Technol, 2004; 147: 343
[4]
Guo J T.Materials Science and Engineering for Superalloys. Vol.2, Beijing: Science Press, 2008: 127
[4]
(郭建亭. 高温合金材料学(中册). 北京: 科学出版社, 2008: 127)
[5]
Jackson M P, Reed R C.Mater Sci Eng, 1998; A259: 85
[6]
Pang H T, Reed P A S.Int J Fatigue, 2008; 30: 2009
[7]
Qu J L, Du J H, Bi Z N, Wang M Q, Zhang J, Wu G L.J Iron Steel Res, 2011; 23(suppl2): 247
The Editorial Board of China Aeronautical Materials Handbook. China Aeronautical Materials Handbook. Vol.2, 2nd Ed., Beijing: Standards Press of China, 2002: 271
