Inhomogeneity Analyses of Microstructure and Mechanical Properties of TC21 Titanium Alloy Variable Cross-section Die Forgings for Aviation
YANG Jie1,2, HUANG Sensen2, YIN Hui3, ZHAI Ruizhi3, MA Yingjie1,2(), XIANG Wei3, LUO Hengjun3, LEI Jiafeng1,2, YANG Rui1,2
1School of Materials Science and Engineering, University of Science and Technology of China, Shenyang 110016, China 2Shi -changxu Innovation Center for Advanced Materials, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China 3China National Erzhong Group Deyang Wanhang Die Forging Co. Ltd., Deyang 618000, China
Cite this article:
YANG Jie, HUANG Sensen, YIN Hui, ZHAI Ruizhi, MA Yingjie, XIANG Wei, LUO Hengjun, LEI Jiafeng, YANG Rui. Inhomogeneity Analyses of Microstructure and Mechanical Properties of TC21 Titanium Alloy Variable Cross-section Die Forgings for Aviation. Acta Metall Sin, 2024, 60(3): 333-347.
TC21 titanium alloy has been successfully used in the structural die forgings of aviation owing to its excellent damage tolerance. However, because of the difference in the equivalent strains of die forgings, the microstructure and properties of variable cross-sections are considerably different, affecting the service life of the structural parts. Therefore, the microstructure and mechanical properties of β-forged TC21 titanium alloy die forgings with variable cross-sections were characterized using Deform software simulation, OM, SEM, XRD, EBSD, and tensile and impact tests, and the primary factors affecting the tensile and impact properties as well as their anisotropy were comprehensively analyzed. The results showed that the overall shape of the die forgings was complex and the effective strain was concentrated in the range of 0.75-1.20. The evidence of the flow was obvious at high strain, the substructure increased, and the narrow cross-section led to a faster cooling rate. This resulted in the decrease of αp content and refinement of αs, which together led to the increase in strength. The evolution of various texture components under high strain during thermal deformation and heat treatment was analyzed, and finally the strong texture of residual β phase <110>//LD and {0002} weak texture of transformed α phase were formed. The strength anisotropy caused by the strong texture was analyzed from α phase slip system and β phase densely packed plane. The impact load-displacement curves showed that the impact energy was mainly consumed via the initiation energy. Combining with the prior β grain arrangement, the fracture modes of impact and tensile fracture in different orientations were discussed. Finally, a tensile fracture model was proposed, which explained the reason that there was a good strength and plastic matching at a high strain of 1.20. This work provides material research support for optimizing the uniformity design of TC21 alloy variable cross-section die forgings.
Fund: National Natural Science Foundation of China(51871225);National Natural Science Foundation of China(U2106215);Deyang City Science and Technology Project(2021JBJZ011)
Corresponding Authors:
MA Yingjie, professor, Tel: 13840026329, E-mail: yjma@imr.ac.cn
Fig.1 Macrostructures (a) and effective strain distributions (b) of TC21 alloy die forgings (Numbers in Fig.1a show the effective strains at locations I-VI, VD—vertical direction, ND—normal direction, LD—lateral direction)
Fig.2 OM (a1-f1) and SEM (a2-f2) images at positions Ⅰ (a1, a2), Ⅱ (b1, b2), Ⅲ (c1, c2), Ⅳ (d1, d2), Ⅴ (e1, e2), and Ⅵ (f1, f2) in TC21 die forgings (αp—primary α phase, αGB—grain boundary α phase, αs—secondary α phase)
Fig.3 Pole figures of {0002} and {100} for the α phase at positions Ⅱ (a), Ⅲ (b), Ⅴ (c), and Ⅵ (d) in Fig.1a
Fig.4 Pole figures of {110} and {200} for the β phase at positions Ⅱ (a), Ⅲ (b), Ⅴ (c), and Ⅵ (d) in Fig.1a
Fig.5 Sections (φ2 = 45°) of orientation distribution function (ODF) maps of β phase at positions Ⅱ (a), Ⅲ (b), Ⅴ (c), and Ⅵ (d) in Fig.1a (φ1, φ2, Φ—Euler angles)
Fig.6 Analyses of low magnified orientation maps and pole figures of α + β and the Burgers orientation relationship between αGB and β grains on both sides at position Ⅱ in Fig.1a (a) α orientation map and the corresponding pole figures (b) β orientation map and the corresponding pole figures (c) pole figures showing that αGB maintains the Burgers orientation relationship with both β1 and β2 in the box
Phase
β forging
α + β solution treatment
Aging treatment
β matrix
<110>//LD
Weaker
Preserved
αp
Grain boundary α phase texture
Preserved
Preserved
Intragranular α phase texture
Stronger
Preserved
αs
-
-
Several variants (Overlaps αp)
Table 1 Texture components evolution of TC21 alloy during hot deformation and heat treatment
Fig.7 High magnified SEM image and corresponding α + β orientation maps and pole figures at position Ⅱ in Fig.1a (a) microstructure of the αp and βt (b) corresponding β orientation map (c) corresponding α orientation map (d) pole figures
Fig.8 Room temperature tensile curves of TC21 alloy die forgings along LD at different positions (Inset shows the details in the box of the original curves)
Position
Rp0.2MPa
RmMPa
A
%
Z
%
I
J
Ⅰ
1084 ± 3
1210 ± 5
5.0 ± 3.3
11.0 ± 4.3
27.0 ± 1.5
Ⅱ
1063 ± 5
1198 ± 10
9.0 ± 1.5
14.0 ± 2.5
33.0 ± 2.0
Ⅲ
1042 ± 6
1171 ± 7
8.0 ± 2.4
11.5 ± 3.2
32.0 ± 1.0
Ⅳ
1040 ± 6
1156 ± 6
8.8 ± 1.5
14.5 ± 3.5
36.0 ± 2.5
Ⅴ
1014 ± 2
1137 ± 3
11.3 ± 1.7
16.0 ± 2.4
40.0 ± 2.0
Ⅵ
1010 ± 4
1125 ± 4
8.0 ± 2.0
15.5 ± 2.5
38.0 ± 1.5
Table 2 Mechanical properties of TC21 alloy die forgings along LD at different positions
Fig.9 Analyses of α + β orientation maps (a1, a2), local misorientations (LMs) (b1, b2), BSE images (c1, c2), and phase proportions (d1, d2) at positions Ⅱ (a1-d1) and Ⅵ (a2-d2) in Fig.1a (Insets in Figs.9b1 and b2 show the frequency (F) distributions of LM)
Position
Direction
Rp0.2 / MPa
Rm / MPa
A / %
Z / %
I / J
Ⅱ
LD
1063 ± 5
1198 ± 10
9.0 ± 1.5
14.0 ± 2.5
33.0 ± 2.0
ND
1043 ± 3
1185 ± 5
8.0 ± 2.0
10.0 ± 3.5
30.9 ± 2.1
Ⅴ
LD
1014 ± 2
1137 ± 3
11.3 ± 1.7
16.0 ± 2.4
40.0 ± 2.0
ND
1013 ± 3
1138 ± 4
6.5 ± 2.5
11.0 ± 3.0
36.0 ± 3.5
Table 3 Tensile and impact properties at positions Ⅱ and Ⅴ in Fig.1a along LD and ND
Fig.10 Typical displacement-load curves at position Ⅱ in Fig.1a along LD (a) and ND (b) (Fmax—maximum load, WE—impact energy obtained from the experimental curve, WF—impact energy obtained by fitting the curve, Wi—crack initiation energy, Wp—crack propagation energy)
Fig.11 Typical impact fracture morphologies at position Ⅱ in Fig.1a along LD (a-c) and ND (d-f)
Fig.12 Typical tensile fracture morphologies at position Ⅱ in Fig.1a along LD (a-c) and ND (d-f) (Insets show the side macro-morphologies of the corresponding tensile fracture)
Fig.13 Inverse pole figures at positions Ⅱ (a, b) and Ⅴ (c, d) in Fig.1a along LD (a, c) and ND (b, d) (The black and blue contour lines are the Schmid's factors for basal and prismatic slip in orientation triangle, respectively)
Fig.14 Schematics of tensile process of prior β grains at position Ⅱ in Fig.1a along LD (a) and ND (b)
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