Hot Deformation Behavior and Microstructural Characteristics of Ti-46Al-8Nb Alloy

doi:10.1007/s40195-018-0742-4

Abstract

Abstract:

Hot deformation behavior, microstructural evolution and flow softening mechanism were investigated in Ti-46Al-8Nb alloy via isothermal compression approach. The true stress-strain curves exhibited typical work hardening and flow softening, in which the dependence of the peak stress on temperature and strain rate was obtained by hyperbolic sine equation with Zener-Hollomon (Z) parameter, and the activation energy was calculated to be 446.9 kJ/mol. The microstructural analysis shows that the alternate dark and light deformed ribbons of Al-rich and Nb-rich regions appeared and were associated with local flow involving solute segregation. The Al segregation promoted flow softening mainly arising from the recrystallization of γ phase with low stacking fault energy. The coarse recrystallized γ and several massive γ phase were observed at grain boundaries. While in the case of Nb segregation, β/B2 phase harmonized bending of lamellae, combined with the growth of recrystallized γ grains and α+β+γ→α+γ transition under conditions of temperature and stress, leading to the breakdown of α₂/γ lamellar colony. During the hot compression process, gliding and dissociation of dislocations occurred in γ phase that acted as the main softening mechanism, leading to extensive γ twins and cross twins in α/γ lamellae and at grain boundaries. In general, homogeneous microstructure during the hot deformation process can be obtained in TiAl alloy with high Nb addition and low Al segregation. The deformation substructures intrinsically promote the formability of Ti-46Al-8Nb alloy.

Key words: Titanium aluminides, Deformation behavior, Activation energy, Dynamic recrystallization, Local flow softening

Tian-Rui Li, Guo-Huai Liu, Mang Xu, Tian-Liang Fu, Yong Tian, Ra-Ja Devesh Kumar Misra, Zhao-Dong Wang. Hot Deformation Behavior and Microstructural Characteristics of Ti-46Al-8Nb Alloy[J]. Acta Metallurgica Sinica (English Letters), 2018, 31(9): 933-944.

Figures/Tables 11

Fig. 1 Macrostructure a and microstructure of $\alpha_{2} /\gamma$ lamellae b, γ phase at lamellar boundaries c and B2 phase in lamellar colony d in the as-cast Ti-46Al-8Nb alloy.

Fig. 2 True stress-strain curves at different strain rates obtained from the isothermal compression tests of Ti-46Al-8Nb alloy at: a 1100 °C, b 1150 °C, c 1200 °C, d 1250 °C.

Fig. 3 Relationship between peak stress and deformation conditions for the Ti-46Al-8Nb alloy: a $\ln \sigma_{\rm{p}}{-}\ln (\dot{\varepsilon })$, b $\sigma_{\rm{p}}{-}\ln (\dot{\varepsilon })$), c $\ln [\sinh (\alpha \sigma_{\rm{p}} )]{-}\ln (\dot{\varepsilon })$, d $1000/T{-}\ln \left[ {\sinh \left( {\alpha \sigma_{\rm{p}} } \right)} \right]$ .

Fig. 4 Relationship between peak stress and Z parameter.

Table 1 Activation energy and peak stress of TiAl alloys during high-temperature compression deformation [11, 24, 25, 26]

Composition (at.%)	Initial microstructure	T (°C)	$\dot{\varepsilon }$ (s^-1)	σ_p (MPa)	Q (kJ/mol)
Ti-45Al-7Nb-0.3W	Near γ, HIP	1050-1200	1×10⁰-1×10^-3	140	414
Ti-47Al-1V	Nearly lamellar (IM)	1000-1200	1×10⁰-1×10^-3	125	404
Ti-43.9Al-4.3Nb-(Mo, B)	Nearly lamellar, HIP	1100-1250	1×10⁰-1×10^-2	60	540.3
Ti-45Al-7Nb-0.4W	Nearly lamellar (PM)	1000-1200	1×10^-1-1×10^-3	160	420
Ti-46Al-8Nb [this work]	Nearly lamellar (IM)	1100-1250	1×10⁰-1×10^-3	255	446.9

Fig. 5 Microstructures of hot-deformed Ti-46Al-8Nb alloys at different $\ln Z$ values: a $\ln Z = 36.85$ (1100 °C/0.1 s-1), b $\ln Z = 33.17$ (1150 °C/0.01 s-1), c $\ln Z = 31.89$ (1200 °C/0.01 s-1), d $\ln Z = 30.69$ (1250 °C/0.01 s-1) and the insertion shows the detailed view of the white box, e $\ln Z = 29.58$ (1200 °C/0.001 s-1), f $\ln Z = 28.39$ (1250 °C/0.001 s-1) .

Fig. 6 Microstructures of Al-segregated region in the hot-deformed Ti-48Al-8Nb alloy with the different Z values: a $\ln Z = 37.77$ (1150 °C/1 s-1) and the inset shows a detailed view of the white box, b $\ln Z = 35.47$ (1150 °C/0.1 s-1), c$\ln Z = 31.89$ (1200 °C/0.01 s-1), d $\ln Z = 29.58$ (1200 °C/0.001 s-1) .

Fig. 7 TEM micrographs of deformed γ phase in Al-segregated region. a γ sub-grains induced by dislocation movement, b mechanical twins in γ grains, c dislocations pileup at the boundaries and intersection of the twins in γ grains, d DRX γgrains induced by $1/6 < 11\bar{2}]${111} twins.

Fig. 8 Microstructures in Nb-rich region in hot-deformed Ti-46Al-8Nb alloy. a bending lamellar and elongated B2 phase, b deformation ribbon in Nb-enriched region and the inset shows detailed view of white box, c, d the bending lamellae and detailed microstructure.

Fig. 9 EBSD images of the evolution of bending lamellar colony of Ti-46Al-8Nb alloy. a Image quality (IQ) map, b phase map overlaid with high- and low-angle grain boundaries, c grain orientation spread (GOS) map, d inverse pole figure (IPF) map.

Fig. 10 Bright-field TEM images of the microstructures of hot-deformed Ti-46Al-8Nb alloy: a γ twins and growth of γ grains, b multiple-phase structure in the kink region, c retained lamellae, d recrystallized grains and sub-grain structure.

References

[1]	F. Appel, M. Oehring, R. Wagner, Intermetallics 8, 1283 (2000)
[2]	J.J. Xin, L.Q. Zhang, G.W. Ge, J.P. Lin, Mater. Des. 107, 406(2016)
[3]	G.H. Liu, Z.D. Wang, T.L. Fu, Y. Li, H.T. Liu, T.R. Li, M.N. Gong, G.D. Wang, J. Alloys Compd. 650, 45(2015)
[4]	H.Z. Niu, Y.Y. Chen, S.L. Xiao, F.T. Kong, C.J. Zhang, Intermetallics 19, 1767 (2011)
[5]	W.Y. Gui, G.J. Hao, Y.F. Liang, F. Li, X. Liu, J.P. Lin, Appl. Surf. Sci. 389, 1161(2016)
[6]	L. Cheng, H. Chang, B. Tang, H.C. Kou, J.S. Li, Adv. Mater. Res. 510, 723(2012)
[7]	Z.C. Liu, J.P. Lin, S.J. Li, G.L. Chen, Intermetallics 10, 653 (2002)
[8]	H.Z. Niu, F.T. Kong, Y.Y. Chen, F. Yang, J. Alloys Compd. 509, 10179(2011)
[9]	B. Liu, Y. Liu, Y.P. Li, W. Zhang, A. Chiba, Intermetallics 19, 1184 (2011)
[10]	H. Clemens, W. Wallgram, S. Kremmer, V. Güther, A. Otto, A. Bartels, Adv. Eng. Mater. 10, 707(2008)
[11]	B. Liu, Y. Liu, W. Zhang, J.S. Huang, Intermetallics 19, 154 (2011)
[12]	X.J. Xu, L.H. Xu, J.P. Lin, Y.L. Wang, Z. Lin, G.L. Chen, Intermetallics 13, 337 (2005)
[13]	G.L. Chen, X.J. Xu, Z.K. Teng, Y.L. Wang, J.P. Lin, Intermetallics 15, 625 (2007)
[14]	Z.W. Huang, Scr. Mater. 52, 1021(2005)
[15]	X.J. Xu, L. Song, Y.F. Liang, J.P. Lin, T. Mater, Heat Treat. 36, 79(2015)
[16]	Y.F. Liang, X.J. Xu, L.P. Lin, Rare Met. 35, 15(2016)
[17]	Z.F. Xu, X.J. Xu, J.P. Lin, Y. Zhang, Y.L. Wang, Z. Lin, G.L. Chen, J. Aeronaut. Mater. 27, 28(2007)
[18]	Z.F. Xu, X.J. Xu, J.P. Lin, Y. Zhang, Y.L. Wang, Z. Lin, G.L. Chen, J. Mater. Eng. 9, 42(2007)
[19]	H.Z. Li, Z. Li, W. Zhang, Y. Wang, Y. Liu, H.J. Wang, J. Alloys Compd. 508, 359(2010)
[20]	Z.H. Huang, Intermetallics 13, 245 (2005)
[21]	T.T. Cheng, Intermetallics 7, 995 (1999)
[22]	T.T. Cheng, M.H. Loretto, Acta Mater. 46, 4801(1998)
[23]	G.H. Liu, X.Z. Li, Y.Q. Su, D.M. Liu, J.J. Guo, H.Z. Fu, J. Alloys Compd. 541, 275(2012)
[24]	H.Y. Kim, W.H. Sohn, S.H. Hong, Mater. Sci. Eng., A 251, 216 (1998)
[25]	S.S. Li, X.K. Su, Y.F. Han, X.J. Xu, G.L. Chen, Intermetallics 13, 323 (2005)
[26]	S.W. Zeng, A.M. Zhao, H.T. Jiang, X.N. Ding, D. Peng, Mater. Sci. Eng., A 661, 160 (2016)
[27]	J.B. Li, Y. Liu, B. Liu, Y. Wang, P. Cao, C.X. Zhou, C.J. Xiang, Y.H. He, Intermetallics 52, 49 (2014)
[28]	L. Cheng, X.Y. Xue, B. Tang, H.C. Kou, J.S. Li, Intermetallics 49, 23 (2014)
[29]	Y. Wang, Y. Liu, G.Y. Yang, J.B. Li, B. Liu, J.W. Wang, H.Z. Li, Mater. Sci. Eng., A 577, 210 (2013)
[30]	R.M. Imayev, V.M. Imayev, M. Oehring, F. Appel, Metall. Mater. Trans. A 36, 859 (2005)
[31]	W.J. Zhang, F. Appel, Mater. Sci. Eng., A 334, 59 (2002)
[32]	Z.G. Lu, J. Wu, Guo P. Ru, L. Xu, R. Yang, Acta Metall. Sin. (Engl. Lett.) 30, 621(2017)
[33]	S.L. Semiatin, B.W. Shanahan, F. Meisenkothen, Acta Mater. 58, 4446(2010)
[34]	C.T. Liu, P.J. Maziasz, Intermetallics 6, 653 (1998)
[35]	Y.H. Wang, J.P. Lin, Y.H. He, X. Lu, Y.L. Wang, G.L. Chen, J. Alloys Compd. 461, 367(2008)
[36]	Y.Y. Chen, B.H. Li, F.T. Kong, J. Alloys Compd. 457, 265(2008)