Hot Tensile Behaviors and Microstructure Evolution of Ti-6Al-4V Titanium Alloy Under Electropulsing

doi:10.1007/s40195-018-0735-3

Abstract

Abstract:

The effect of electropulsing on the mechanical behaviors and microstructures of Ti-6Al-4V titanium alloy was investigated by an uniaxial tensile test. Compared to the value measured in cold tensile test, the alloy exhibits lower ultimate tensile strength when the tensile deformation is assisted by electropulsing. The tensile elongation is found to vary non-monotonically with increasing root mean square (RMS) current density. Though decreasing at first, the tensile elongation increases with current density once the value exceeds 8.1 A/mm². Through applying current with RMS current density of 12.7 A/mm², the tensile elongation at strain rate 0.001 s^-1 can be improved by 94.1%. In addition, it is observed that more remarkable electroplastic effect is induced by the higher peak current density under similar thermal effect. Microstructure analysis reveals that the low plasticity at 8.1 A/mm² is attributed to the micro-void easily formation near the tips of acicular β phases. The enhanced ductility at higher current densities, on the other hand, is attributed to the dynamic recrystallization.

Key words: Ti-6Al-4V alloy, Electropulsing, Mechanical properties, Microstructure, Fracture morphology

Dong-Wei Ao, Xing-Rong Chu, Shu-Xia Lin, Yang Yang, Jun Gao. Hot Tensile Behaviors and Microstructure Evolution of Ti-6Al-4V Titanium Alloy Under Electropulsing[J]. Acta Metallurgica Sinica (English Letters), 2018, 31(12): 1287-1296.

Figures/Tables 13

Fig. 1 Optical micrograph of as-received specimens

Table 1 Chemical compositions of the Ti6Al4V sheet specimens (wt%)

Al	V	Fe	C	O	N	H	Ti
6.0	4.1	0.19	0.02	0.16	0.02	0.002	Bal.

Fig. 2 a Experimental set-up; b waveform of electropulsing (ti is pulse duration, to is pulse interval, Ip is peak current, tp is period)

Table 2 Experimental parameters

	Strain rates (s^-1)	Electropulsing parameters
	Strain rates (s^-1)	Voltage (V)	Frequency (Hz)	Duration (μs)	J _r (A/mm^-2)	J _p (A/mm^-2)	t_i/t_p
Group Ι	0.010 0.005 0.001	20	150	64.0	8.1	103.9	0.0096
		20	250	62.8	10.0	103.9	0.0157
		20	350	63.5	11.6	103.9	0.0222
		20	450	62.4	12.7	103.9	0.0281
Group ΙΙ	0.005	28	135	62.0	11.1	169.5	0.0084
Group ΙΙ	0.005	30	130	62.4	12.5	186.7	0.0081

Fig. 3 a Temperature field distribution; b temperature evolution of Ti-6Al-4V alloy with 8.1-12.7 A/mm2, 0.005 s-1; c relationship between temperature curve and flow stress-strain curve; d the maximum temperature evolution under RMS current density and strain rates

Fig. 4 Representative stress-strain curves under electropulsing: a Jr?=?0-12.7 A/mm2, Jp?=?103.9 A/mm2, ε?=?0.001 s-1, b Jr?=?12.7 A/mm2, Jp?=?103.9 A/mm2, \(\dot{\varepsilon }\)?=?0.01-0.001 s-1

Fig. 5 a Variation of strain hardening exponent n; b ultimate tensile strength evolution under different RMS current densities and strain rates; c variation of strain rate sensitivity exponent m; d elongation to fracture under different RMS current densities and strain rates

Fig. 6 a Temperature field of specimens with Jp?=?103.9-169.5 A/mm2 at Jr?=?11.1-11.6 A/mm2, Jp?=?103.9-186.7 A/mm2 at Jr?=?12.5-12.7 A/mm2, b representative stress-strain curves corresponding to Fig. 6a, b temperature field

Fig. 7 XRD patterns for EPT specimens in fracture zone

Fig. 8 Optical microstructure images of Ti-6Al-4V alloy under different RMS current densities and strain rates: a 0 A/mm2, 0.001 s-1, b 8.1 A/mm2, 0.001 s-1, c 11.6 A/mm2, 0.001 s-1, d 12.7 A/mm2, 0.001 s-1, e 8.1 A/mm2, 0.01 s-1, f 12.7 A/mm2, 0.01 s-1

Fig. 9 Fracture morphology among a section shrinkage evolution under RMS current density and 0.001 s-1; b without current, 0.001 s-1, c 8.1 A/mm2, 0.001 s-1, d 11.6 A/mm2, 0.001 s-1, e 11.6 A/mm2, 0.005 s-1, f 11.6 A/mm2, 0.01 s-1

Fig. 10 Dependencies of volume fracture of β phase and β particle spacing on RMS current density

Fig. 11 Fracture morphologies under a 8.1 A/mm2, 0.001 s-1; b 11.5 A/mm2, 0.001 s-1

References

[1]	F.H. Li, X.H. Yi, J.L. Zhang, Z.G. Fan, D.T. Gong, Z.P. Xi, Acta Metall. Sin. (Engl. Lett.) 23, 293(2010)
[2]	G.L. Ma, Y.H. Lu, C. Zhu, Acta Metall. Sin. (Engl. Lett.) 13, 665(2000)
[3]	S.D. Ji, A.L. Zhou, Y.M. Yue, G.H. Luan, Y.Y. Jin, F. Li, Acta Metall. Sin. (Engl. Lett.) 25, 365(2012)
[4]	P. Guo, Y. Zhao, W. Zeng, Q. Hong, Mater. Sci. Eng., A 563, 106 (2013)
[5]	M.J. Kim, K. Lee, K.H. Oh, I.S. Choi, H.H. Yu, S.T. Hong, H.N. Han, Scripta Mater. 75, 58(2014)
[6]	J.H. Roh, J.J. Seo, S.T. Hong, M.J. Kim, H.N. Han, J.T. Rorh, Int. J. Plast. 58, 84(2014)
[7]	X. Ye, X. Li, G. Song, G. Tang, J. Alloys Compd. 616, 173(2014)
[8]	Y. Zhou, G.Q. Chen, X.S. Fu, W.L. Zhou, Trans. Nonferrous Metals Soc. China 24, 1012 (2014)
[9]	X. Li, B. Ji, Q. Zhou, J. Chen, P. Gao, J. Mater. Eng.Perform. 25, 4514(2016)
[10]	H. Song, Z.J. Wang, T.J. Gao, Trans. Nonferrous Metals Soc. China 17, 87 (2007)
[11]	K. Okazaki, M. Kagawa, H. Conrad, Scripta Mater. 12, 1063(1978)
[12]	K. Okazaki, M. Kagawa, H. Conrad, Scripta Mater. 13, 473(1979)
[13]	O.A. Troitskii, V.I. Likhtman, Soviet Phys. Doklady 8, 332 (1963)
[14]	O.A. Troitskii, Strength Mater. 9, 35(1977)
[15]	O.A. Troitskii, Strength Mater. 16, 277(1984)
[16]	H. Conrad, Mater. Sci. Eng., A 287, 227 (2000)
[17]	K. Okazaki, K. Kagawa, H. Conrad, Mater. Sci. Eng. 45, 109(1980)
[18]	L. Guan, G. Tang, P.K. Chu, J. Mater. Res. 25, 1215(2011)
[19]	X. Ye, G. Tang, G. Song, J. Kuang, J. Mater. Res. 29, 1500(2014)
[20]	X. Ye, Z.T.H. Tse， G. Tang, J. Mater. Res. 30, 206(2014)
[21]	H. Xie, X. Dong, K. Liu, Z. Ai, F. Peng, Q. Wang, F. Chen, J. Wang, Mater. Sci. Eng., A 637, 23 (2015)
[22]	B. Kinsey, G. Cullen, A. Jordan, S. Mates, CIRP Ann. Manuf. Technol. 62, 279(2013)
[23]	J. Magargee, F. Morestin, J. Cao, J. Eng. Mater.Technol. 135, 041003(2013)
[24]	X. Wang, J. Xu, D. Shan, B. Guo, J. Cao, Mater. Des. 127, 134(2017)
[25]	X. Wang, J. Xu, Z. Jiang, W.L. Zhu, D. Shan, B. Guo, J. Cao, Mater. Sci. Eng., A 659, 215 (2016)
[26]	W. Bao, X. Chu, S. Lin, J. Gao, Mater. Sci. Technol. 33, 1(2016)
[27]	J. Deng, Y.C. Lin, S.S. Li, J. Chen, Y. Ding, Mater. Des. 49, 209(2013)
[28]	J. Luo, M. Li, W. Yu, H. Li, Mater. Des. 31, 741(2010)
[29]	X. Ye, J. Kuang, X. Li, G. Tang, J. Alloys Compd. 599, 1(2014)
[30]	X. Ye, Z.T.H. Tse， G. Tang， G. Song, Mater. Charact. 98, 147(2014)
[31]	X. Ye, Z.T.H. Tse， G. Tang， X. Li， G. Song, J. Mater. Process. Technol. 222, 27(2015)
[32]	S.O. Ojediran, O. Ajaja, J. Mater. Sci. 23, 4037(1988)
[33]	W.F. Cui, Z. Jin, A.H. Guo, L. Zhou, Mater. Sci. Eng., A 499, 252 (2009)