Microstructure and Mechanical Properties of As-Cast Ti-Al-V Alloys with Different Proportion of α / β Clusters
ZHU Zhihao1, CHEN Zhipeng1, LIU Tianyu2, ZHANG Shuang3, DONG Chuang1,3(), WANG Qing1
1Key Laboratory of Materials Modification by Laser, Ion and Electron Beams (Ministry of Education), School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024, China 2State Key Laboratory of Light Alloy Casting Technology for High-End Equipment, Shenyang Research Institute of Foundry Co., Ltd. CAM, Shenyang 110022, China 3School of Materials Science and Engineering, Dalian Jiaotong University, Dalian 116028, China
Cite this article:
ZHU Zhihao, CHEN Zhipeng, LIU Tianyu, ZHANG Shuang, DONG Chuang, WANG Qing. Microstructure and Mechanical Properties of As-Cast Ti-Al-V Alloys with Different Proportion of α / β Clusters. Acta Metall Sin, 2023, 59(12): 1581-1589.
The dual-cluster composition formula of the widely-used α + β Ti-6Al-4V and α-{[Al-Ti12](AlTi2)}12 + β-{[Al-Ti14](V2Ti)}5, reported in our previous work, indicates that all Ti alloys are composed of α and β units. In this study, Ti-(3.19-7.45)Al-(0-12.03)V (mass fraction, %) alloys are designed following composition formula of [Al-Ti12](AlTi2)}17 - n + β-{[Al-Ti14](V2Ti)}n by changing n value (number of β cluster units). The alloys as prepared by copper mould suction-casting cover microstructures ranging from pure α to pure β. In the as-cast state, as the n value increases, the microstructure changes from single α phase (α' martensite), via α + β dual-phase, and finally to single β phase. The morphology of α' martensite gradually changes from plate-like to lamellar and needle-like. Ti-6Al-4V alloy corresponds to n = 5, where β phase begins to appear. When n = 8, needle-like α' martensite shows the highest content. When n = 12, α phase disappears completely and is replaced by β phase. Correspondingly, the strength of the alloys increases first and then decreases, while the plasticity changes inversely, due to the presence of fine-needle α' martensite. Among all the compositions, Ti-5.28Al-6.14V alloy (n = 8) shows the highest strength (about 90 MPa higher than Ti-6Al-4V), with tensile strength of 1019 MPa, yield strength of 867 MPa. Its specific strength and hardness of 230 kN·m/kg and 0.76 GPa·cm3/g increased by 9% and 5%, respectively, are both superior to Ti-6Al-4V.
Fund: National Basic Research Program of China(2020JCJQZD165);Key Discipline and Major Project of Dalian Science and Technology Innovation Foundation(2020JJ25CY004)
Fig.1 Twinned cuboctahedron with coordination number of 12 (a) and rhombic dodecahedron with coordination number of 14 (b) as the nearest-neighbor clusters of hcp and bcc structures, respectively. The nearest-neighbor shell of the latter cluster is composed of two sub-shells
Material code
n
Composition / (mass fraction, %)
[Mo]eq
[Al]eq
∆TL-S / oC
n0
0
Ti-7.45Al
0.0
7.5
4.9
n1
1
Ti-7.16Al-0.82V
0.6
7.2
4.9
n2
2
Ti-6.87Al-1.62V
1.1
6.9
4.7
n3
3
Ti-6.60Al-2.41V
1.4
6.6
4.5
n4
4
Ti-6.32Al-3.19V
2.1
6.3
9.4
n5
5
Ti-6.05Al-3.94V
2.6
6.1
13.3
n7
7
Ti-5.53Al-5.45V
3.6
5.5
20.7
n8
8
Ti-5.28Al-6.14V
4.1
5.3
24.3
n12
12
Ti-4.30Al-8.87V
5.9
4.3
31.8
n17
17
Ti-3.19Al-12.03V
8.0
3.1
35.1
Table 1 Designed compositions following different numbers of β units (n) and their Al- and Mo-equivalents and solidification ranges
Fig.2 Ti-Al-V ternary composition chart, where are marked the compositions of the designed series, α-[Al-Ti12]Al1Ti2, and some β formulas. The resigned alloy series lie along the straight line (in red) linking α-Al2Ti14 and β-Al1Ti15V2
Fig.3 XRD spectra of as-cast Ti-Al-V alloys
Fig.4 OM images of typical Ti-Al-V alloys of n1 (a), n2 (b), n5 (c), n8 (d), n12 (e), and n17 (f)
Fig.5 SEM images of typical as-cast Ti-Al-V alloys of n1 (a), n2 (b), n5 (c), and n8 (d)
Fig.6 Room-temperature mechanical properties of as-cast Ti-Al-V alloys (a) engineering stress-strain curves (b) ultimate tensile strength and elongation
Fig.7 Comparison of mechanical properties between data (this work, as-cast, room temperature) with those of heat-treated Ti-6Al-4V materials[19,20]
Fig.8 Elastic modulus (E) of as-cast Ti-Al-V alloys
Fig.9 Vickers hardnesses (a), mass densities (b), specific hardnesses (c), and specific strengthes (d) of Ti-Al-V alloys (Specific hardness denotes the hardness-over-density ratio, and specific strength denotes the ultimate tensile strength-over-density ratio, respectively)
Fig.10 Low (a, c, e, g) and high (b, d, f, h) magnified fracture morphologies of as-cast Ti-Al-V alloys (a, b) n1 (c, d) n5 (e, f) n8 (g, h) n12
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