Ultrafine grained metastable Ti6Al4V5Cu alloy with high strength and excellent low-cycle fatigue property

doi:10.1016/j.jmst.2022.05.007

Abstract

Abstract:

The insufficient low-cycle fatigue properties of titanium alloys under cyclic heavy loading are regarded as a challenge for their security in service. In recent years, a large number of studies have found that the transformation induced plasticity (TRIP) effect could hinder the propagation of fatigue cracks, which significantly improved the low-cycle fatigue properties of titanium alloys. However, the coarse β-phase grains and the soft phase transformation product α″ phase in TRIP titanium alloys impair their tensile strength, which restrict their applications in engineering. To this end, a Ti6Al4V5Cu alloy with TRIP effect was developed in this work. It was proposed to use the mutual restraint between the α and β phases in the material to refine the grains, and through composition optimization, the phase transformation product would be the α' phase, which has a higher strength than the α″ phase. Thus, the strength of the Ti6Al4V5Cu alloy can be improved. The results showed that the tensile strength and elongation of the TRIP Ti6Al4V5Cu alloy was 1286 MPa and 22%, which was 23.7% and 46.7% higher than that of the traditional Ti6Al4V alloy, respectively. Besides, under the same strain amplitude, the fatigue life of the Ti6Al4V5Cu alloy was 2-5 times longer than that of the Ti6Al4V alloy. Furthermore, we clarified the mechanisms of improving the tensile strength and fatigue properties of the Ti6Al4V5Cu alloy, which would lay a research foundation for the development of high-performance titanium alloys.

Key words: Transformation induced plasticity, Ti alloys, Low-cycle fatigue, Work hardening, Crack propagation

Wei Song, Hai Wang, Yi Li, Shuyuan Zhang, Ling Ren, Ke Yang. Ultrafine grained metastable Ti6Al4V5Cu alloy with high strength and excellent low-cycle fatigue property[J]. J. Mater. Sci. Technol., 2022, 129: 240-250.

Figures/Tables 13

Table 1. Chemical compositions of the experimental alloys.

	Element (wt%)
	Al	V	Cu	Fe	C	N	H	O	Ti
Ti6Al4V5Cu	5.75	3.78	5.36	0.10	0.011	0.002	0.002	0.06	Bal.
Ti6Al4V	6.03	3.96	-	0.05	0.040	0.010	0.005	0.11	Bal.

Fig. 1. Initial microstructures of the Ti6Al4V5Cu and the Ti6Al4V alloys. (a, b) Phase distribution figures; (c, d) IPFs of the α phase; (e, f) IPFs of the β phase.

Fig. 2. α phase ODF maps of the Ti6Al4V5Cu (a) and the Ti6Al4V (b) alloy; β phase ODF maps of the Ti6Al4V5Cu (c) and the Ti6Al4V(d) alloy.

Fig. 3. Tensile properties of the Ti6Al4V5Cu alloy and the Ti6Al4V alloy. (a) Engineering stress-strain curve; (b) comparison of tensile properties of the Ti6Al4V5Cu alloy with other titanium alloys; (c) work hardening rate-true strain curve; (d) true stress-true strain curve in cyclic tensile and uniaxial tensile tests of the Ti6Al4V5Cu alloy.

Fig. 4. Low-cycle fatigue properties of the Ti6Al4V5Cu and the Ti6Al4V alloys. (a) Strain amplitude-cycle number curve; (b) hysteresis loop at the strain amplitude of Δεt/2 = 1.6%; (c, d) stress amplitude-cycle number curves of the Ti6Al4V5Cu alloy and the Ti6Al4V alloys under different strain amplitudes, respectively; (e, f) Hysteresis loops of the Ti6Al4V5Cu and the Ti6Al4V alloys at half-life cycles under different strain amplitude, respectively.

Table 2. Low-cycle fatigue properties of the two experimental alloys.

		Ti6Al4V5Cu						Ti6Al4V
Δε_t/2 (%)	Life (cycles)	Stable stress (MPa)	Δε_p/2 (%)	I_β	W_β (%)	Life ( cycles)	Stable stress (MPa)	Δε_p/2 (%)	I_β	W_β/ (%)
0.8	21,716	663.4	0.01	0.88	37.1	4872	497.8	0.11	0.18	10.7
1.0	8388	894.4	0.13	0.37	19.8	4057	568.4	0.25	0.17	10.2
1.2	3408	962.4	0.20	0.12	7.91	832	652.5	0.40	0.14	8.6
1.4	1586	1012.1	0.32	0.04	3.15	526	720.5	0.62	0.15	9.1
1.6	624	1047.6	0.45	0.02	1.31	349	752.3	0.74	0.15	9.1

Fig. 5. XRD patterns of the Ti6Al4V5Cu (a) and Ti6Al4V (b) alloys.

Fig. 6. TEM microstructure observations of the Ti6Al4V5Cu alloy before and after fatigue test with different strain amplitudes: (a) initial microstructure; (b) Δεt/2 = 0.8%; (c) Δεt/2 = 1.0%; (d) Δεt/2 = 1.2%; (e) Δεt/2 = 1.4%; (f) Δεt/2 = 1.6%.

Fig. 7. TEM microstructure observations of the Ti6Al4V alloy before and after fatigue test with different strain amplitudes: (a) initial microstructure; (b) Δεt/2 = 0.8%; (c) Δεt/2 = 1.0%; (d) Δεt/2 = 1.2%; (e) Δεt/2 = 1.4%; (f) Δεt/2 = 1.6%.

Fig. 8. TEM observations of the Ti6Al4V5Cu alloy after fatigue test under the strain amplitude of Δεt/2 = 1.6%. (a) BF image; (b) mapping of Al element; (c) mapping of Cu element; (d) diffraction pattern of α′ phase in area I; (e) BF image of area I; (f) DF image of area I; (g) HRTEM observation of area II; (h) HRTEM observation of area III; (i) HRTEM simulated image of area III showing dislocations.

Fig. 9. Fractured surfaces of the Ti6Al4V5Cu (a) and Ti6Al4V (b) alloys under the strain amplitude of Δεt/2 = 1.6%.

Fig. 10. Fatigue growth rates of the Ti6Al4V5Cu and the Ti6Al4V alloys.

Fig. 11. Fracture longitudinal sections of the Ti6Al4V5Cu (a) and Ti6Al4V (b) alloys.

References 31

[1]	A. Czerwinski, R. Lapovok, D. Tomus, Y. Estrin, A. Vinogradov, J. Alloy. Compd. 509 (2011) 2709-2715. DOI URL
[2]	X. Feng, X. Pan, W. He, P. Liu, Z. An, L. Zhou, Int. J. Fatigue 149 (2021) 106270. DOI URL
[3]	X.P. Jiang, C.S. Man, M.J. Shepard, T. Zhai, Mater. Sci. Eng. A (2007) 137- 143 468-470.
[4]	N. Tsuji, S. Tanaka, T. Takasugi, Surf. Coat. Technol. 203 (2009) 1400-1405. DOI URL
[5]	S. Kumar, K. Chattopadhyay, V. Singh, J. Alloy. Compd. 724 (2017) 187-197. DOI URL
[6]	S. Carabajar, C. Verdu, A. Hamel, R. Fougères, Mater. Sci. Eng. A 257 (1998) 225-234. DOI URL
[7]	M.G. de Mello, F.H. Costa, V. Opini, A. Resende, A. Cremasco, R. Caram, Mater. Res. 23 (2020).
[8]	Q. Xue, Y.J. Ma, J.F. Lei, R. Yang, C. Wang, J. Mater. Sci. Technol. 34 (2018) 2507-2514. DOI
[9]	Y. Jung, K. Lee, S.J. Hong, J.K. Lee, J. Han, K.B. Kim, P.K. Liaw, C. Lee, G. Song, J. Alloy. Compd. 886 (2021) 161187. DOI URL
[10]	G. Zhao, X. Xu, D. Dye, P.E.J. Rivera-Díaz-del-Castillo, N. Petrinic, Scr. Mater. 208 (2022) 114362. DOI URL
[11]	L. Choisez, A. Elmahdy, P. Verleysen, P.J. Jacques, Acta Mater. 220 (2021) 117294. DOI URL
[12]	C.L. Li, X.J. Mi, W.J. Ye, S.X. Hui, Y. Yu, W.Q. Wang, Mater. Sci. Eng. A 578 (2013) 103-109. DOI URL
[13]	T. Wang, H. Guo, Y. Wang, X. Peng, Y. Zhao, Z. Yao, Mater. Sci. Eng. A 528 (2011) 2370-2379. DOI URL
[14]	H.H. Mehrer, Diffusion in Solid Metals and Alloys, Springer Materials, 1990.
[15]	S. Hanada, N. Masahashi, T.K. Jung, Mater. Sci. Eng. A 588 (2013) 403-410. DOI URL
[16]	Y.D. Zhang, G.P. Li, C.Z. Liu, F.S. Yuan, F.Z. Han, Ali. Muhanmmad, H.F. Gu, Chin. J. Mater. Res. 33 (2019) 443-451.
[17]	H. Wu, Y.Q. Zhao, P. Ge, W. Zhou, Rare Metal Mat. Eng. 41 (2012) 805-810.
[18]	Y. Ito, N. Hoshi, T. Hayakawa, C. Ohkubo, H. Miura, K. Kimoto, Mater. Sci. Eng. B 245 (2019) 30-36. DOI URL
[19]	S. Panda, S.K. Sahoo, A. Dash, M. Bagwan, G. Kumar, S.C. Mishra, S. Suwas, Mater. Charact. 98 (2014) 93-101. DOI URL
[20]	Q. Xu, W. Li, Y. Yin, J. Zhou, H. Nan, Mater. Sci. Eng. A 832 (2022) 142496. DOI URL
[21]	W.Y. Liu, Y.H. Lin, Y.H. Chen, T.H. Shi, S. Ambrish, Rare Metal Mat. Eng. 46 (2017) 634-639. DOI URL
[22]	R.G. Pigeon, A. Varma, J. Mater. Sci. Lett. 11 (1992) 1370-1372. DOI URL
[23]	Y. Chong, G. Deng, S. Gao, J. Yi, A. Shibata, N. Tsuji, Scr. Mater. 172 (2019) 77-82. DOI URL
[24]	B. Wang, L. Cheng, D. Li, Int. J. Fatigue 156 (2022) 106668. DOI URL
[25]	J.F. Xiao, X.K. Shang, J.H. Hou, Y. Li, B.B. He, Int. J. Plast. 146 (2021) 103103. DOI URL
[26]	Y.G. Li, M.H. Loretto, D. Rugg, W. Voice, Acta Mater 49 (2001) 3011-3017. DOI URL
[27]	Q. Luo, Y. Guo, B. Liu, Y. Feng, J. Zhang, Q. Li, K. Chou, J. Mater. Sci. Technol. 44 (2020) 171-190. DOI
[28]	Q. Li, Y. Lu, Q. Luo, X. Yang, Y. Yang, J. Tan, Z. Dong, J. Dang, J. Li, Y. Chen, B. Jiang, S. Sun, F. Pan, J. Magn. Alloys 9 (2021) 1922-1941.
[29]	O. Slávik, T. Vojtek, L. Poczklán, H.A. Tinoco, T. Kruml, P. Hută r, M. Šmíd, Theor. Appl. Fract. Mech. 118 (2022) 103212. DOI URL
[30]	A .A. Griﬃth, Philos. Trans. R. Soc. Lond. Ser. A, Containing Pap. Math. Phys. Character 221 (1921) 163-198.
[31]	E. Orowan, Rep. Prog. Phys. 12 (1949) 185-232. DOI URL