Microstructure and fracture toughness of the Bridgman directionally solidified Fe-Al-Ta eutectic at different solidification rates

doi:10.1016/j.jmst.2019.09.041

Abstract

Abstract:

Fe-Al-Ta eutectic composites were obtained by a modified Bridgman directional solidification technique at different solidification rates. Solidification microstructure transforms from regular eutectic to eutectic colony with the increase of the solidification rate. The solid/liquid interface of Fe-Al-Ta eutectic evolves from planar interface to cellular interface with the increase of the solidification rate. In addition, three-point bending method was adopted to study the room-temperature fracture toughness of the as-cast Fe-Al-Ta eutectic alloy and the Fe-Al-Ta eutectic composites. Moreover, the fracture morphologies, the crack propagation path and the strengthening mechanism of Fe-Al-Ta eutectic were discussed.

Key words: Directional solidification, Eutectic composite, Solid/liquid interface, Fracture toughness, Fracture morphology

Chunjuan Cui, Cong Wang, Pei Wang, Wei Liu, Yuanyuan Lai, Li Deng, Haijun Su. Microstructure and fracture toughness of the Bridgman directionally solidified Fe-Al-Ta eutectic at different solidification rates[J]. J. Mater. Sci. Technol., 2020, 42: 63-74.

Figures/Tables 22

Fig. 1. Schematic diagram of the size of the three-point bending specimen.

Fig. 2. Longitudinal microstructures of the Fe-Al-Ta eutectic alloys at different solidification rates: (a) 6 μm/s; (b) 30 μm/s; (c) 80 μm/s; (d) 200 μm/s.

Fig. 3. Transverse microstructures of the Fe-Al-Ta eutectic alloys at different solidification rates: (a) 6 μm/s; (b) 30 μm/s; (c) 80 μm/s; (d) 200 μm/s.

Table 1 Lamellar or rod spacing of Fe-Al-Ta eutectic at different solidification rates.

Solidification rate (μm/s)	Lamellar or rod spacing (μm)
6	7.34
30	4.03
80	2.92
200	1.15

Fig. 4. Relationship between the lamellar or rod spacing and the solidification rate.

Fig. 5. Solid/liquid interface morphologies of the Fe-Al-Ta eutectic at different solidification rates: (a) 6 μm/s; (b) 30 μm/s; (c) 80 μm/s; (d) 200 μm/s.

Table 2 GL/R values of Fe-Al-Ta eutectic at different solidification rates.

Solidification rate (μm/s)	G_L/R (K s cm^-2)
6	250,000
30	50,000
80	18,750
200	7,500

Fig. 6. The varying curves of S(λ) changed by solidification rate.

Fig. 7. Three-point bending load-displacement curves of Fe-Al-Ta eutectic composites in as-cast and different solidification rates.

Table 3 KIC test values of Fe-Al-Ta eutectic.

Solidification rate (μm/s)	F_Q (N)	a (mm)	f(a/w)	P_max/P_q	Effectiveness determination	K_IC (MPa m^1/2)
6	766.91	0.971	1.055	1.07	Effective	16.71
30	333.14	0.791	0.958	1.00	Effective	5.49
80	283.92	0.770	0.945	1.00	Effective	4.60
200	587.44	0.950	1.042	1.06	Effective	10.53
As-cast	499.17	1.031	1.087	1.05	Effective	9.34

Table 4 Volume fractions of the strengthening phase at different solidification rates.

Solidification rate (μm/s)	Volume fraction (%) [19]
6	31.24
30	21.09
80	18.89
200	38.03

Fig. 8. Fracture morphologies of as-cast Fe-Al-Ta eutectic alloy: (a) 30×; (b) 100×; (c) 1000×; (d) 2000×.

Fig. 10. Fracture morphologies of directional solidified Fe-Al-Ta eutectic composites: (a-c) 30 μm/s; (d-f) 80 μm/s.

Fig. 11. High magnification photographs for (a) Fig. 10(b) and (b) Fig. 10(c) of the directionally solidified Fe-Al-Ta eutectic composite at the solidification rate of 30 μm/s.

Fig. 12. Fracture morphologies of the directionally solidified Fe-Al-Ta eutectic omposite at the solidification rate of 200 μm/s: (a) 30×; (b) 100×; (c) 500×; (d) 1000×.

Fig. 13. Fracture morphologies of directional solidified Fe-Al-Ta eutectic composite at the solidification rate of 200 μm/s: (a) 500×; (b) 2000×.

Fig. 14. Crack propagation path in the side surface of Fe-Al-Ta eutectic: (a) as-cast alloy; (b) 6 μm/s; (c) 30 μm/s; (d) 80 μm/s; (e) 200 μm/s.

Fig. 15. Typical crack propagation path of Fe-Al-Ta eutectic composites: (a) crack blunting and crack nucleation; (b) crack bridging; (c) interface debonding.

Fig. 16. Illustration of the crack bridging model [26].

Fig. 17. Illustrations of the crack blunting model and crack nucleation model [27].

Fig. 18. Illustration of the interface debonding model [27].

References

[1]	F. Stein, M. Palm, G. Sauthoff, Intermetallics 12 (2004) 713-720.
[2]	R.V. Shankar, V.S. Raja, Intermetallics 11 (2003) 119-128.
[3]	Q. Ren, H.J. Su, J. Zhang, B. Yao, W.D. Ma, L. Liu, H.Z. Fu, T.W. Huang, M. Guo, W.C. Yang, J. Alloys Compd. 662(2016) 634-639.
[4]	K.S. Zhu, W.H. Ma, K.X. Wei, Y. Lei, J.F. Hu, T.L. Lv, Y.N. Dai, J. Alloys Compd. 750(2018) 102-110.
[5]	R.V. Reyes, R. Kakitani, T.A. Costa, J.E. Spinelli, N. Cheung, A. Garcia, J. Philos. Mag. Lett. 96(2016) 1-10.
[6]	Y.G. Wen, C.J. Cui, L.L. Tian, M. Yang, T. Xue, J. Mater. Rev. 30(2016) 116-120.
[7]	G. Chen, J. Li, H. Fu, J. Mater. Rev. 13(1995) 5-7.
[8]	A. Ohno, Theory, Practice and Application of Metal Solidification, Mechanical Industry Press, Bingjing, 1990.
[9]	H.Z. Fu, F.Q. Xie, J. Sci. Technol. Adv. Mater. 2(2001) 193-196.
[10]	H. Wang, J. Zhang, C.J. Cui, L. Liu, H.Z. Fu, J. Mater. Eng. 1268(2008) 71-75.
[11]	C.J. Cui, P. Wang, M. Yan, Y.G. Wen, C.Q. Ren, S.Y. Wang, Phys. Med. 124(2018) 12-19.
[12]	C.J. Cui, S.Y. Wang, M. Yang, Y.G. Wen, P. Wang, C.Q. Ren, J. Wuhan Univ.Technol.-Mater. Sci. 34(2019) 656-661.
[13]	C.J. Cui, C.Q. Ren, Y.Y. Liu, S.Y. Wang, H.J. Su, J. Alloys Compd. 785(2019) 62-71.
[14]	K.A. Jackson, J. Dynam. Curved Fronts 1 (1988) 363-376.
[15]	J.W. Rutter, B. Chalmers, Can. J. Phys. 31(1953) 15-39.
[16]	W.W. Mullins, R.F. Sekerka, J. Appl. Phys. 35(1964) 444-451.
[17]	R.F. Sekerka, J. Appl. Phys. 36(1965) 264-268.
[18]	K. Gao, Study on Growth Morphology, Orientation and Mechanical Properties of Directionally Solidified Intermetallic Compound Al2Cu Phase, Ph.D. Thesis, Northwestern Polytechnical University, 2014 (in Chinese).
[19]	M. Yang, Directional Solidification Microstructure of Fe-Al-Ta Eutectic Alloy, Ph.D. Thesis, Xi’an University of Architecture and Technology, 2016 (in Chinese).
[20]	S.Q. Lu, B.Y. Huang, Y.H. He, S.F. He, Y.D. Deng, J. Mater. Eng. 5(2003) 43-47.
[21]	Z. Shang, Microstructure and Mechanical Properties of Directionally Solidified NiAl-Cr(Mo) Alloy with High Temperature Gradient, Ph.D. Thesis, Northwestern Polytechnical University, 2015 (in Chinese).
[22]	Y.J. Du, J. Shen, Y.L. Xiong, Z. Shang, L. Wang, H.Z. Fu, Mater. Sci. Eng. A 621 (2015) 94-99.
[23]	M.E. Launey, R.O. Ritchie, Adv. Mater. 21(2009) 2103-2110.
[24]	Y.P. Zheng, W.D. Zeng, D. Li, Q.Y. Zhao, X.B. Liang, J.W. Zhang, X. Ma, J. Alloys Compd. 709(2017) 511-518.
[25]	M.G. Mendiratta, R. Goetz, D.M. Dimiduk, J.J. Lewandowski, Metall. Mater. Trans. A 26 (1995) 1767-1776.
[26]	A.G. Evans, R.M. Mcmeeking, Acta Metall. 34(1986) 2435-2441.
[27]	K.S. Chan, J. Mater. Proc. 364(1994) 469-480.