Effects of β-Dendrite Growth Velocity on β → α Transformation of Hypoperitectic Ti-46Al-7Nb Alloy

doi:10.1007/s40195-014-0167-7

Abstract

Abstract:

Solidification characteristics of Ti-46Al-7Nb melts were studied by the electromagnetic levitation technique. A maximum melt undercooling up to 240 K has been achieved. When the undercooling is lower than the critical value ΔT* = 205 K, the alloy possesses typical hypoperitectic solidification characteristic which can be evidenced by a peritectic layer observed in the as-solidified microstructure. However, the Widmanstätten structure can be observed at large undercooling regime of ΔT≥ΔT*, where peritectic reaction cannot proceed and γ lamellar precipitation within α plates is suppressed. Based on the BCT dendrite growth model, the dendrite growth velocities were calculated as a function of undercooling. Theoretical analysis indicates that the growth mechanism of the primary β phase transforms from solutal-diffusion-controlled to thermal-diffusion-controlled in the undercooling range of 188-205 K, which can be attributed to the onset of solute trapping at the critical undercooling. Meanwhile, with increasing undercooling, the solute trapping effect becomes more dominant as a consequence.

Key words: TiAl alloy, Dendrite growth, Undercooling, Microstructure

Tan He, Rui Hu, Jun Wang, Jie-Ren Yang, Jin-Shan Li. Effects of β-Dendrite Growth Velocity on β → α Transformation of Hypoperitectic Ti-46Al-7Nb Alloy[J]. Acta Metallurgica Sinica (English Letters), 2015, 28(1): 58-63.

Figures/Tables 8

Fig. 1 Section of the phase diagram of TiAl-7.5Nb calculated with ThermoCalc and MatCalc [18]

Fig. 2 Temperature-time characteristics of primary recalescence events of undercooled Ti-46Al-7Nb alloys with different undercoolings

Fig. 3 SEM back-scattered electron images showing the microstructures of Ti-46Al-7Nb alloy with different undercoolings (arrows indicate the zones for solute concentration measurements): a ΔT = 10 K; b ΔT = 54 K; c ΔT = 94 K; d ΔT = 188 K; e ΔT = 205 K; f ΔT = 226 K; g ΔT = 240 K

Fig. 4 XRD patterns of samples solidified under different undercoolings

Table 1 Parameters of Ti-46Al-7Nb alloy used for calculations

Parameter	Value and unit	Ref.
Liquid temperature, T _m	1,868 K	Exp.
Latent heat of fusion, ΔH _f	14.23 kJ/mol	[27]
Specific heat capacity, C _p	32.72 J/(mol K)	[28]
Diffusion coefficient, D _l	3.5 × 10^-9 (m²/s)	[29]
Equilibrium partition coefficient, k ₀	0.63	[30]
Thermal-diffusion coefficient, α	0.71	[29]
Speed of sound, V ₀	3,000 (m/s)	Constant
Slope of the liquidus line, m	-9.14 (K/at%)	[30]
Interfacial energy, σ	0.216 (J/m²)	[31]
Thermal diffusivity in liquid, α _l	4.9 × 10^-6 (m²/s)	[28]

Fig. 5 Partial undercoolings versus bulk undercooling of Ti-46Al-7Nb alloy

Fig. 6 Calculated growth velocities of β dendrite versus the undercooling

Fig. 7 Solute concentrations in the interdendritic zone of Ti-46Al-7Nb alloys versus undercooling

References 32

[1]	J.P. Lin, L.L. Zhao, G.Y. Li, L.Q. Zhang, X.P. Song, F. Ye, G.L. Chen, Intermetallics 19, 131 (2011)
[2]	W.J. Zhang, G.L. Chen, F. Apple, T.G. Nieh, S.C. Deevi,Mater. Sci. Eng. 315, 250(2001)
[3]	X.J. Xu, J.P. Lin, Z.K. Teng, Y.L. Wang, G.L. Chen,Mater. Lett. 61, 369(2007)
[4]	L. Huang, P.K. Liaw, C.T. Liu, Y. Liu, J.S. Huang, Trans. Nonferrous Met.Soc.China 21, 2192 (2011)
[5]	D.M. Herlach, Mater. Sci.Eng.R 12, 177 (1994)
[6]	P.R. Algoso, W.H. Hofmeister, R.J. Bayuzick,Acta Mater. 51, 4307(2003)
[7]	W.L. Wang, Y.J. Lu, H.Y. Qin, B. Wei,Sci. China G. 52, 720(2009)
[8]	H.P. Wang, W.J. Yao, B. Wei,Appl. Phys. Lett. 89, 201905(2006)
[9]	W.J. Yao, B. Wei, Sci.China E 46, 549 (2003)
[10]	W.J. Yao, X.L. Niu, L. Zhou, N. Wang, J. Lee, Acta Metall.Sin. (Engl. Lett.) 26, 523(2013)
[11]	H. Hartmann, P.K. Galenko, D. Holland-Moritz, M. Kolbe, D.M. Herlach, J. Appl.Phys. 103, 073509(2008)
[12]	J. Chang, H.P. Wang, K. Zhou, B. Wei, J. Appl.Phys.A 109, 139 (2012)
[13]	Y. Ruan, F.P. Dai, Intermetallics 25, 80 (2012)
[14]	M. Barth, B. Wei, D.M. Herlach, Phys.Rev.B 51, 3422 (1995)
[15]	M. Schwarz, A. Karma, K. Eckler, D.M. Herlach,Phys. Rev. Lett. 73, 1380(1994)
[16]	W.L. Wang, H.Y. Qin, Z.C. Xia, B. Wei,Chin. Sci. Bull. 57, 1073(2012)
[17]	F.H. Froes, C. Suryanarayana, D. Elizer, J. Mater. Sci. 27, 5113(1992)
[18]	H.F. Chladil, H. Clemens, H. Leitner,Adv. Eng. Mater. 12, 1131(2005)
[19]	J.Y. Jung, J.K. Park, C.H. Chun, Intermetallics 7, 1033 (1999)
[20]	E. Schwaighofer, B. Rashkova, H. Clemens, A. Stark, S. Mayer, Intermetallics 46, 173 (2014)
[21]	D.R. Johnson, K. Chihara, H. Inui, M. Yamaguchi,Acta Mater. 18, 6529(1998)
[22]	O. Shuleshova, W. Loser, D. Holland-Moritz, D.M. Herlach, J. Ecker, J. Mater. Sci. 47, 4497(2012)
[23]	C.D. Anderson, W.H. Hofmeister, R.J. Bayuzick, Metall.Trans.A 23, 2699 (1992)
[24]	Y.Z. Chen, F. Liu, G.C. Yang, N. Liu, C.L. Yang, Y.H. Zhou,Scr. Mater. 57, 779(2007)
[25]	W.J. Boettinger, S.R. Coriell, R. Trivedi,in Rapid Solidification Processing: Principles and Technologies IV, ed. by R. Mehrabian, P.A. Parish(Claitor’s Publishing Division, Baton Rouge, 1988), pp. 13-25
[26]	J.H. Kim, S.W. Kim, H.N. Lee, M.H. Oh, H. Inui, D.M. Wee, Intermetallics 13, 1038 (2005)
[27]	I. Egry, R. Brooks, D. Holland-Moritz, R. Novakovic, T. Matsushita, E. Ricci, S. Seetharaman, R. Wunderlich, D. Jarvis,Int. J. Thermophys. 28, 1026(2007)
[28]	K. Zhou, H.P. Wang, B. Wei,Philos. Mag. Lett. 93, 138(2013)
[29]	K. Zhou, H.P. Wang, J. Chang, B. Wei,Philos. Mag. Lett. 90, 455(2010)
[30]	V.T. Witusiewicz, A.A. Bondar, U. Hecht, T. Ya,Velikanova. J. Alloys Compd. 472, 133(2009)
[31]	F. Spaepen, R.B. Meyer,Scr. Mater. 10, 257(1976)
[32]	F. Liu, H.F. Wang, S.J. Song, K. Zhang, G.C. Yang, Y.H. Zhou,Prog. Phys. 32, 1(2012)