Effect of W Content on the Phase Transformation Behavior in Ti-42Al-5Mn- xW Alloy
LI Xiaobing1, QIAN Kun1, SHU Lei1, ZHANG Mengshu1, ZHANG Jinhu2, CHEN Bo1(), LIU Kui1
1.Department of Materials Science and Technology Research, Ji Hua Laboratory, Foshan 528200, China 2.Shi-changxu Innovation Center for Advanced Materials, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
Cite this article:
LI Xiaobing, QIAN Kun, SHU Lei, ZHANG Mengshu, ZHANG Jinhu, CHEN Bo, LIU Kui. Effect of W Content on the Phase Transformation Behavior in Ti-42Al-5Mn- xW Alloy. Acta Metall Sin, 2023, 59(10): 1401-1410.
Advanced intermetallic β-solidifying γ-TiAl-based alloys have various potential applications in the aerospace and automobile industries due to their low density, functionality at higher temperatures, and high specific strength/modulus. The crucial aspect that needs to be considered when developing a new β-solidifying γ-TiAl alloy is to clarify the influence law of β-stabilizer elements on the phase transformation behavior of γ-TiAl alloys. In this work, the impact of W contents (0.5%-1.0%, atomic fraction) on the phase transformation behavior and microstructure characteristics of Ti-42Al-5Mn-xW (atomic fraction) alloy with low cost and superior temperature workability was systematically investigated. The findings demonstrate that there were minor changes in the β-phase single region temperature (Tβ ) and γ phase solvus temperature (Tγ-solv); furthermore, the eutectoid reaction temperature (Teut) increases with the W content from 0.5% to 1.0%. Addition of W influences the solid phase transformation pathway to a certain extent. When the concentration of W increases to 0.5%, the equilibrium phase of the alloy at near service temperature gradually changes from α2 + γ + Laves to βo + α2 + γ + Laves. Additionally, W addition will also have a substantial effect on the lamellar microstructure. The volume fraction of lamellar microstructure considerably decreased after alloying with (0.5%-1.0%)W for Ti-42Al-5Mn alloy when being treated in the (γ + α + β) triple-phase region followed by furnace cooling. Increasing the W content to 0.8% and 1.0% results in the development of γ and βo grain phases with almost complete removal of α2/γ lamellar structures. However, the W-free and W-bearing Ti-42Al-5Mn alloys show near complete lamellar structures when treated in (α + β) two-phase region followed by furnace cooling. Furthermore, when the content of W increased from 0.5% to 1.0%, an equiaxed grain structure with refined lamellar colonies is typically obtained.
Table 1 Chemical compositions of the Ti-42Al-5Mn-xW alloys
Fig.1 DSC curves of the Ti-42Al-5Mn-xW with x = 0.5 (a) and1.0 (b)
Fig.2 Back scattering electron (BSE) images of Ti-42Al-5Mn-0.5W alloy after annealing at 1160oC (a), 1170oC (b), 1180oC (c), 1210oC (d), 1220oC (e), 1230oC (f), 1320oC (g), and 1330oC (h) for 1 h，and then water cooling (WC) (γg—γ grain, γlamellae—γ lamellae)
Fig.3 Effects of W concentration on the phase transformation temperature in Ti-42Al-5Mn-xW (The data of Ti-42Al-5Mn is quoted from Ref.[14]. Teut—eutectoid reaction temperature, Tγ-solv—γ phase solvus temperature, Tβ —β-phase single region temperature)
Fig.4 BSE images of Ti-42Al-5Mn-xW alloys with x = 0 (a1-a3), x = 0.5 (b1-b3), x = 0.8 (c1-c3), and x = 1.0 (d1-d3) after annealing at 1200oC for 1 h and then WC (a1-d1), air cooling (AC) (a2-d2), and furnace cooling (FC) (a3-d3) (Insets in Figs.4a1 and a2 show the high magnified images. γp—γ platelet)
x
WC
AC
FC
α2/γ region
γg
βo
α2/γ region
γg
βo
α2/γ region
γg
βo
0
87.4 ± 0.2
3.8 ± 0.1
8.9 ± 0.2
74.5 ± 0.9
14.6 ± 0.9
10.9 ± 0.8
69.2 ± 0.4
24.8 ± 0.5
6.1 ± 0.6
0.5
63.3 ± 0.7
13.9 ± 0.5
22.8 ± 0.9
54.3 ± 1.1
19.2 ± 0.4
26.5 ± 1.7
23.9 ± 0.3
59.8 ± 0.5
16.3 ± 0.6
0.8
54.8 ± 0.8
15.5 ± 0.8
29.7 ± 0.7
41.5 ± 1.1
24.6 ± 1.1
33.9 ± 1.1
15.9 ± 0.4
62.6 ± 0.5
21.5 ± 0.9
1.0
58.4 ± 0.6
9.5 ± 0.7
32.1 ± 0.4
56.9 ± 1.1
13.1 ± 0.6
30.0 ± 0.9
18.1 ± 0.5
60.2 ± 0.9
21.7 ± 1.3
Table 2 Quantitative statistical results of microstructures for Ti-42Al-5Mn-xW alloys treated at 1200oC for 1 h and then cooled with different methods
Fig.5 BSE images of Ti-42Al-5Mn-xW alloys with x = 0 (a1-a3), x = 0.5 (b1-b3), x = 0.8 (c1-c3), and x = 1.0 (d1-d3) after annealing at 1300oC for 1 h and then WC (a1-d1), AC (a2-d2), and FC (a3-d3) (Insets in Figs.5a1-d1 show the high magnified images)
x
WC
AC
FC
α2
βo
α2
βo + γp region
α2/γ region
γg
βo
0
76.1 ± 0.3
23.9 ± 0.3
83.4 ± 0.3
16.6 ± 0.3
71.3 ± 0.4
20.5 ± 0.3
8.2 ± 0.2
0.5
60.1 ± 0.5
39.9 ± 0.5
64.6 ± 0.5
35.4 ± 0.5
55.0 ± 1.5
29.5 ± 2.5
15.5 ± 0.5
0.8
49.2 ± 1.0
50.8 ± 1.0
77.5 ± 0.6
22.5 ± 0.6
39.0 ± 0.5
41.8 ± 0.4
19.2 ± 0.3
1.0
36.8 ± 0.4
63.2 ± 0.4
80.8 ± 1.1
19.2 ± 1.1
45.8 ± 0.5
31.5 ± 0.7
22.7 ± 0.9
Table 3 Quantitative statistical results of microstructures for Ti-42Al-5Mn-xW alloys treated at 1300oC for 1 h and then cooled with different methods
Fig.6 Calculated phase diagram of Ti-42Al-5Mn-xW (x = 0-2) (The investigated alloys with the nominal composition Ti-42Al-5Mn-0.5W and Ti-42Al-5Mn-1.0W are indicated by vertical lines. L—liquid; letters a, b, and c indicate Teut, Tγ-solv, and Tβ, respectively)
Fig.7 Microstructures of Ti-42Al-5Mn-0.5W after aging at 800oC for 720 h (a) EPMA-BSE image (b) an enlarged view of the box in Fig.7a (c) EBSD image
Phase
Ti
Al
Mn
W
γ
52.30 ± 0.62
44.43 ± 1.31
3.02 ± 0.18
0.31 ± 0.37
βo
55.36 ± 0.13
32.03 ± 0.54
10.64 ± 0.30
2.16 ± 0.15
α2
60.23 ± 0.34
33.82 ± 0.42
5.13 ± 1.23
0.89 ± 0.71
Laves
40.91 ± 1.26
30.00 ± 0.51
28.52 ± 1.83
0.51 ± 0.18
Table 4 Chemical compositions of the different phases in the original βo region for the Ti-42Al-5Mn-0.5W after aging at 800oC for 720 h used by EPMA-EDS
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