Chemical, microstructure, and mechanical property of TiAl alloys produced by high-power direct laser deposition

doi:10.1016/j.jmst.2021.07.062

Abstract

Abstract:

Additive manufactured metals sometimes exhibit extraordinary microstructures and mechanical properties due to the particular processes. In this paper, we focus on a novel gradient TiAl alloys fabricated by high-power direct laser deposition, whose chemical composition, microstructure, and mechanical property vary along the building direction. The results indicate that Al concentration dramatically decreases from 39.5 at.% to 30.1 at.% as the height increases from the bottom to the top. Meanwhile, microstructural characterization indicates that the specimen appears basket-weave microstructure at the bottom, then the α₂ and γ phase gradually decrease, and eventually it transforms into acicular martensite microstructure in the top region. The indentation analysis shows that the associated hardness increases as the height increases, while the plasticity reaches a minimum value in the middle region. The increasing amount of β_o(ω) is considered to be responsible for the increasing hardness because of the strong precipitation strengthening effect. The high plasticity in the bottom and top regions results from the strong deformation behaviors of the γ and β_o phases.

Key words: Direct laser deposition, TiAl alloys, Inhomogeneity, Microstructure, Mechanical properties

Xinyu Zhang, Chuanwei Li, Mengyao Zheng, Xudong Yang, Zhenhua Ye, Jianfeng Gu. Chemical, microstructure, and mechanical property of TiAl alloys produced by high-power direct laser deposition[J]. J. Mater. Sci. Technol., 2022, 117: 99-108.

Figures/Tables 14

Table 1. Chemical composition of the initial powder.

Powder	Elemental chemical composition
Powder	Ti	Al	Cr	Nb
Atom percent (at.%)	Bal.	47.7	1.86	2.05
Weight percent (wt.%)	Bal.	33.1	2.5	4.9

Fig. 1. (a) Schematic of the DLD process, in which the red arrows represent the back-and-forth scanning strategy, and the dotted rectangle represents the specimen extracted from the deposited wall; (b) OM image of the as-deposited sample and indentations along the building direction, which are marked as No. 1 to No. 80 from the bottom to the top, respectively; and (c) Linear EDS measurement corresponding to the yellow line in (b).

Fig. 2. (a-d) BSE images of the as-deposited specimen at regions A, B, C and D, respectively, and the inserted image in (a) is the phase distribution map obtained by EBSD, where yellow represents the βo phase, red represents the α2 phase, and blue represents the γ phase. (e) Phase fractions corresponding to the locations in (a-d).

Table 2. Chemical composition of the phases at regions A-C.

Regions	Phase	Elemental chemical composition (at.%)
Regions	Phase	Ti	Al	Cr	Nb
A	β_o	Bal.	38.1	2.9	2.6
Empty Cell	α₂	Bal.	42.0	1.5	2.2
Empty Cell	γ	Bal.	44.9	1.3	2.3
B	β_o	Bal.	37.3	2.2	2.7
Empty Cell	α₂	Bal.	39.6	1.3	2.3
C	β_o	Bal.	35.8	1.8	2.8
Empty Cell	α₂	Bal.	35.7	1.3	2.5

Fig. 3. (a-c) Bright field (BF) images of the microstructures at regions A, B, and C, respectively, and the corresponding SAED patterns are inserted; (d) BF image of the microstructure in the top region (Region D), and the related SAED patterns along the <112>βo and <113>βo directions; (e) Bright field (DF) image of the ω particles corresponding to (d); and (f) high-resolution TEM image of the ω and βo phases.

Fig. 4. (a) Load-depth curve and (b) Vickers hardness and plasticity parameter δH at regions A, B, C and D.

Fig. 5. Deformed microstructural morphology at Region A. (a, b) BF image and its corresponding SAED pattern along the <1120>a2 direction; (c, d) two-beam images of the α2 lath corresponding to g=<0002> and $g=\langle \bar{1}102\rangle $, respectively.

Fig. 6. TEM morphology of the γ grain at Region A. (a, b) BF image and its corresponding SAED pattern along the <001>γ direction; (c, d) two-beam images of the γ grain corresponding to g=〈110〉 and g=〈 $1\bar{1}0$〉, respectively.

Fig. 7. TEM morphology of the βo(ω) matrix at Region A. (a, b) BF image and its corresponding SAED pattern along the <001>γ direction; (c) DF image of the ω precipitates dispersed in the βo matrix; and (d) two-beam image corresponding to g=〈$\bar{1}10$〉.

Fig. 8. Deformed microstructural morphology at Region C. (a) BF image under the indentation; (b) corresponding DF image of the βo(ω) matrix; and (c) magnified two-beam image corresponding to the red rectangle in (a).

Fig. 9. Deformed microstructural morphology at Region D. (a) BF image under the indentation; (b, c) magnified two-beam images corresponding to the red rectangles in (a), which present the deformation behavior of the βo(ω) matrix and α’ martensite, respectively.

Fig. 10. The load-depth curves of nanoindentation measurement for α2, βo(ω) and γ phases, respectively.

Fig. 11. (a) Phase fractions of the as-deposited specimen along the building direction; (b) corresponding Vickers hardness and plasticity parameter δH.

Fig. 12. Variation in the phase fraction in the equilibrium state when the Al concentration increases from 28 at.% to 40 at.%.

References 37

[1]	K. Kothari, R. Radhakrishnan, N.M. Wereley, Prog. Aerosp. Sci. 55 (2012) 1-16. DOI URL
[2]	F. Appel, U. Brossmann, U. Christoph, S. Eggert, P. Janschek, U. Lorenz, J. Mul-lauer, M. Oehring, J.D.H. Paul, Adv. Eng. Mater. 2 (2000) 699-720. DOI URL
[3]	X. Wu, Intermetallics 14 (2006) 1114-1122. DOI URL
[4]	J. Wang, Q. Luo, H. Wang, Y. Wu, X. Cheng, H. Tang, Addit. Manuf. 32 (2020) 101007.
[5]	M. Todai, T. Nakano, T. Liu, H.Y. Yasuda, K. Hagihara, K. Cho, M. Ueda, M. Takeyama, Addit. Manuf. 13 (2016) 61-70.
[6]	L.E. Murr, S.M. Gaytan, A. Ceylan, E. Martinez, J.L. Martinez, D.H. Hernandez, B.I. Machado, D.A. Ramirez, F. Medina, S. Collins, R.B. Wicker, Acta Mater. 5 (2010) 1887-1894.
[7]	Y. Wu, S. Zhang, X. Cheng, H. Wang, J. Alloys Compd. 799 (2019) 325-333. DOI URL
[8]	L. Lober, F.P. Schimansky, U. Kuhn, F. Pyczak, J. Eckert, J. Mater. Process. Tech- nol. 214 (2014) 1852-1860.
[9]	Y. Ma, D. Cuicui, H. Li, H. Li, Z. Pan, C. Shen, Mater. Sci. Eng. A 657 (2016) 86-95. DOI URL
[10]	S.M. Thompson, L. Bian, N. Shamsaei, A. Yadollahi, Addit. Manuf. 8 (2015) 36-62.
[11]	N. Shamsaei, A. Yadollahi, L. Bian, S.M. Thompson, Addit. Manuf. 8 (2015) 12-35.
[12]	W. Li, J. Liu, Y. Zhou, S. Wen, Q. Wei, C. Yan, Y. Shi, Scr. Mater. 118 (2016) 13-18. DOI URL
[13]	W. Li, J. Liu, S. Wen, Q. Wei, C. Yan, Y. Shi, Mater. Charact. 113 (2016) 125-133. DOI URL
[14]	W. Li, J. Liu, Y. Zhou, S. Wen, J. Tan, S. Li, Q. Wei, C. Yan, Y. Shi, Intermetallics 85 (2017) 130-138. DOI URL
[15]	W. Li, Y. Yang, J. Liu, Y. Zhou, M. Li, S. Wen, Q. Wei, C. Yan, Y. Shi, Acta Mater. 136 (2017) 90-104. DOI URL
[16]	J. Schwerdtfeger, C. Korner, Intermetallics 49 (2014) 29-35. DOI URL
[17]	B.E. Carroll, T.A. Palmer, A.M. Beese, Acta Mater. 87 (2015) 309-320. DOI URL
[18]	Z. Wang, T.A. Palmer, A.M. Beese, Acta Mater. 110 (2016) 226-235. DOI URL
[19]	X. Zhang, C. Li, H. Zhong, X. Yang, J. Gu, Metall. Mater. Trans. A 51A (2020) 82-87.
[20]	X. Zhang, C. Li, M. Zheng, Z. Ye, X. Yang, J. Gu, Addit. Manuf. 32 (2020) 101087.
[21]	X. Zhang, C. Li, M. Zheng, H. Zhong, J. Gu, Mater. Charact. 164 (2020) 110315. DOI URL
[22]	X. Zhang, C. Li, Q. Wang, M. Zheng, Z. Ye, J. Gu, Mater. Res. Lett. 8 (2020) 454-461. DOI URL
[23]	Y. Zhu, X. Tian, J. Li, H. Wang, J. Alloys Compd. 616 (2014) 468-474. DOI URL
[24]	C. Zou, J. Li, W.Y. Wang, Y. Zhang, B. Tang, H. Wang, D. Lin, J. Wang, H. Kou, D. Xu, Comput. Mater. Sci. 152 (2018) 169-177. DOI URL
[25]	R. Banerjee, P.C. Collins, D. Bhattacharyya, S. Banerjee, H.L. Fraser, Acta Mater. 51 (2003) 3277-3292. DOI URL
[26]	Y.V. Mil’Man, Powder Metall. Met. C 38 (1999) 396-402. DOI URL
[27]	R.E. Schafrik, Metall. Trans. A 8 (1977) 1003-1006. DOI URL
[28]	J.P. Hirth, J.L. Lothe, Theory of Dislocations, Wiley, 1982.
[29]	M. Kolb, J.M. Wheeler, H.N. Mathur, S. Neumeier, S. Korte-Kerzel, F. Pyczak, J. Michler, M. Goken, Mater. Sci. Eng. A 665 (2016) 135-140. DOI URL
[30]	M. Schloffer, B. Rashkova, T. Schoberl, E. Schwaighofer, Z. Zhang, H. Clemens, S. Mayer, Acta Mater. 64 (2014) 241-252. DOI URL
[31]	B.E. Carroll, T.A. Palmer, A.M. Beese, Acta Mater. 87 (2015) 309-320. DOI URL
[32]	Z. Wang, T.A. Palmer, A.M. Beese, Acta Mater. 110 (2016) 226-235. DOI URL
[33]	J. Schwerdtfeger, C. Korner, Intermetallics 49 (2014) 29-35. DOI URL
[34]	D. Cormier, O. Harrysson, T. Mahale, H. West, Adv. Mater. Sci. Eng. 2007 (2007) 1-4.
[35]	L.E. Murr, S.M. Gaytan, A. Ceylan, E. Martinez, J.L. Martinez, D.H. Hernandez, B.I. Machado, D.A. Ramirez, F. Medina, S. Collins, R.B. Wicker, Acta Mater. 58 (2010) 1887-1894. DOI URL
[36]	C. Kenel, C. Leinenbach, J. Alloys Compd. 637 (2015) 242-247. DOI URL
[37]	Y. Zhu, J. Li, X. Tian, H. Wang, D. Liu, Mater. Sci. Eng. A 607 (2014) 427-434. DOI URL