Effects of tungsten addition on the microstructural stability and properties of Ti-6.5Al-2Sn-4Hf-2Nb-based high temperature titanium alloys

doi:10.1016/j.jmst.2021.02.057

Abstract

Abstract:

The microstructural evolution, oxidation resistance and mechanical properties of Ti-6.5Al-2Sn-4Hf-2Nb-based alloys with different contents of tungsten (W) additions ranging from 0 to 4.0 wt.% have been investigated in this study. The addition of W changed the microstructure from Widmanstätten colony of the W-free alloy to basketweave microstructure. After thermal exposure at 650 °C for 1000 h, the retained β phase became less continuous, and secondary β nano-particles with high W concentration were precipitated from α lamellas. Within α lamellas, the W was found to mainly partitioned into the secondary β phase and refined the ordered α₂-Ti₃Al precipitates due to increased solubility of Nb in α₂ phase. High W addition increased activation energy for oxidation, promoting the formation of more uniform and compact compound oxides, therefore substantially enhanced the oxidation resistance of the alloy. Besides, the W addition also improved the room and high-temperature yield strength without obviously losing plasticity after long-time thermal exposure. The improved mechanical performance was mainly attributed to the introduction of more α/β interfaces, the precipitation of secondary β phase and the refined α₂ phase with Nb segregation.

Key words: Titanium alloy, High temperature, Microstructure, Oxidation, Mechanical properties

Yaqun Xu, Yu Fu, Juan Li, Wenlong Xiao, Xinqing Zhao, Chaoli Ma. Effects of tungsten addition on the microstructural stability and properties of Ti-6.5Al-2Sn-4Hf-2Nb-based high temperature titanium alloys[J]. J. Mater. Sci. Technol., 2021, 93: 147-156.

Figures/Tables 18

Table 1. Nominal compositions of the studied alloys.

Alloy	Nominal compositions (wt.%)
Alloy	Al	Sn	Hf	Nb	W	Ti
W0	6.5	2	4	2	0	Bal.
W01	6.5	2	4	2	0.1	Bal.
W05	6.5	2	4	2	0.5	Bal.
W10	6.5	2	4	2	1.0	Bal.
W20	6.5	2	4	2	2.0	Bal.
W40	6.5	2	4	2	4.0	Bal.

Fig. 1. Optical microstructures of the Ti-6.5Al-2Sn-4Hf-2Nb-based alloys.

Fig. 2. SEM images take from the transformed β grains of the W0 alloy (a) and W40 alloy (b).

Table 2. Kβ stability coefficients of the studied alloys.

Alloy	W0	W01	W05	W10	W20	W40
K_β	0.056	0.060	0.0783	0.101	0.146	0.237

Fig. 3. SEM images of the (a) W0 and (b) W40 alloys after thermal exposure.

Fig. 4. Bright-field TEM images of the W40 alloy and selected area diffraction patterns were acquired from area (1) and (2), respectively.

Fig. 5. STEM images showing the retained β and secondary β precipitates in W40 alloy.

Table 3. Elemental distribution of β precipitates (wt.%).

Phase	Chemical composition
Phase	Al	Sn	Hf	Nb	W	Ti
Retained β	3.9	1.8	5.5	1.8	34.9	Bal.
Secondary β	4.9	1.9	5.0	2.3	14.1	Bal.
α lamellae	7.7	2.4	3.7	3.1	0.8	Bal.

Fig. 6. Dark-filed TEM images and corresponding SAED patterns (inset) showing the precipitation of ordered α2 phase formed in both (a) W0 and (b) W40 alloys.

Fig. 7. Size and aspect ratios of α2 ordered phase of alloys with different W additions.

Fig. 8. STEM images of the (a) W0 and (b) W40 alloys showing the ordered α2 phase. The locations for EDS analysis were highlighted by numbers, where locations 1 and 3 were α phase, and locations 2 and 4 represented α2 phase.

Table 4. Elemental distribution in the α phase and α2 precipitates.

Alloy	Phase	Chemical composition (wt.%)
Alloy	Phase	Al	Sn	Hf	Nb	W	Ti
W0	α	5.1	4.6	4.9	0.5	0	Bal.
W0	α₂	7.8	6.3	2.9	0.7	0	Bal.
W40	α	6.8	0	6.3	1.0	0.9	Bal.
W40	α₂	8.1	0	2.0	5.1	0	Bal.

Fig. 9. Variations of mass gain with respect to oxidation time of the W-free and W-containing alloys at 750 °C. The Ti1100 and IMI834 are also included for comparison.

Fig. 10. XRD patterns of the specimens oxidized at 750 °C for 700 h.

Table 5. n and kp values of the studied alloys oxidized at 750 °C.

Alloy	n	k_p
W0	1.96	11.1 × 10^-3
W01	1.92	10.9 × 10^-3
W05	1.59	9.6 × 10^-3
W40	2.05	3.9 × 10^-3

Fig. 11. SEM micrographs of oxidized surface morphology of the alloys with different W additions after oxidation in air at 750 °C for 700 h.

Fig. 12. Variation of micro-hardness due to W additions and thermal exposure.

Fig. 13. Compressive mechanical properties at room temperature and 650 °C of the alloys with different W contents before thermal exposure (a) and (b) and after thermal exposure (c) and (d).

References 53

[1]	R.R. Boyer, Mater. Sci. Eng. A, 213(1996), pp. 103-114.
[2]	A.K.J.D.E.J. Gogia, Defence. Sci. J., 55(2005), pp. 149-173.
[3]	F. Sun, J. Li, H. Kou, B. Tang, J. Cai, Mater. Sci. Eng. A, 626(2015), pp. 247-253.
[4]	E.W. Collings, W. Gerhard, R.R. Boyer, ASM International Materials Park(1994).
[5]	V.K. Chandravanshi, A. Bhattacharjee, S.V. Kamat, T.K. Nandy, J. Alloys Compd., 589(2014), pp. 336-345.
[6]	N. Singh, V.J.M.E.Singh Gouthama, E. A, Mater. Sci. Eng. A, 325(2002), pp. 324-332.
[7]	A. Gysler, S. Weissmann, Mater. Sci. Eng. A, 27(1977), pp. 181-193.
[8]	H.J. Wood, G.D.W. Smith, A.C. S, Mater. Sci. Eng. A, 250 (1)(1998), pp. 83-87.
[9]	B. Jiang, D. Wen, Q. Wang, J. Che, C. Dong, P.K. Liaw, F. Xu, L. Sun, J. Mater. Sci. Technol., 35(2019), pp. 1008-1016.
[10]	J. Dai, J. Zhu, C. Chen, F. Weng, J. Alloys Compd., 685(2016), pp. 784-798.
[11]	A. Ebach-Stahl, C. Eilers, N. Laska, R. Braun, Surf. Coat. Technol., 223(2013), pp. 24-31.
[12]	A. Rahmel, Mater. Corros., 39 (1988), p.354.
[13]	Z. Zhang, J. Fan, Z. Wu, D. Zhao, Q. Gao, Q. Wang, Z. Chen, B. Tang, H. Kou, J. Li, J. Alloys Compd., 831(2020), Article 154786.
[14]	J.C. Fisher, Acta Metall, 2(1954), pp. 9-10.
[15]	S. Patu, R.J. Arsenault, Mater. Sci. Eng. A, 194(1995), pp. 121-128.
[16]	S.Z. Zhang, H.Z. Xu, G.P. Li, Y.Y. Liu, R. Yang, Mater. Sci. Eng. A, 408(2005), pp. 290-296.
[17]	A. Radecka, V.A. Vorontsov, J. Coakley, K.M. Rahman, D. Dye, Ordering in α Titanium Alloys, John Wiley & Sons, Inc. (2016).
[18]	J.C. Williams, A.W. Thompson, R.G. Baggerly, Scr. Mater., 8(1974), pp. 625-630.
[19]	G. Welsch, G. Lütjering, K. Gazioglu, W. Bunk, Mater. Trans. A, 8(1977), pp. 169-177.
[20]	J. Li, J. Cai, Y. Xu, W. Xiao, X. Huang, C. Ma, Mater. Sci. Eng. A, 774(2020), Article 138934.
[21]	Q. Wang, J. Liu, R. Yang, J. Aaero. Mater., 14(2014), pp. 13-14.
[22]	W. Jia, W. Zeng, J. Liu, Y. Zhou, Q. Wang, Mater. Sci. Eng. A, 530(2011), pp. 511-518.
[23]	W.L. Xiao, D.H. Ping, Y. Yamabe-Mitarai, J. Mater. Sci., 48(2013), pp. 3363-3369.
[24]	J.-.Y. Xu, Z.-.Z. Shi, Z.-.B. Zhang, H.-.G. Huang, X.-.F. Liu, Corros. Sci., 166(2020), Article 108430.
[25]	T. Kitashima, T. Kawamura, Scr. Mater., 124(2016), pp. 56-58.
[26]	D. Banerjee, J.C. Williams, Acta Mater, 61(2013), pp. 844-879.
[27]	A.G. Imgram, D.N. Williams, H.R. Ogden, J. Les. Com. Metals, 4(1962), pp. 217-225.
[28]	J.D.H. Paul, F. Appel, R. Wagner, Acta Mater, 46(1998), pp. 1075-1085.
[29]	J.M. Cai, M.Y. Hao, X.M. Li, J.M. Ma, C.X. Cao, J. Mater. Eng.(2000), pp. 10-12.
[30]	W.J. Zhang, X.Y. Song, S.X. Hui, W.J. Ye, Y.L. Wang, W.Q. Wang, Mater. Sci. Eng. A, 595(2014), pp. 159-164.
[31]	Y.W. Kim, R. Boyer, Microstructure/property relationships in Titanium Aluminides & alloys, Minerals Metals Mater. Soc.(1991), pp. 337-344.
[32]	Q. Wang, J. Liu, R. Yang, J. Aero. Mater., 34(2014), pp. 1-26.
[33]	G. Wang, Q. Gao, J. Liu, Q. Yang, F. Zheng, Mate. Review(2017).
[34]	W. Li, Z. Chen, J. Liu, Q. Wang, G. Sui, Mater. Sci. Eng. A, 688(2017), pp. 322-329.
[35]	S. Balachandran, A. Kashiwar, A. Choudhury, D. Banerjee, R. Shi, Y. Wang, Acta Mater, 106(2016), pp. 374-387.
[36]	R. Kolli, D.M. Arun, Metals (Basel), 8 (2018), p.506.
[37]	P.L. Narayana, S.-.W. Kim, J.-.K. Hong, N.S. Reddy, J.-.T. Yeom, Mater. Sci. Eng. A, 718(2018), pp. 287-291.
[38]	Q.M. Hu, S.J. Li, Y.L. Hao, R. Yang, B. Johansson, L. Vitos, Appl. Phys. Lett., 93(2008), pp. 58-60.
[39]	K. Yue, J. Liu, H. Zhang, H. Yu, Y. Song, Q. Hu, Q. Wang, R. Yang, J. Mater. Sci. Technol., 36(2020), pp. 91-96.
[40]	A.I. Antipov, V.N. Moiseev, Met.Sci. Heat Treatment, 39(1997), pp. 499-503.
[41]	B. Fu, H. Wang, C. Zou, Z. Wei, Mater. Des., 66(2015), pp. 267-273.
[42]	H.M. Gardner, A. Radecka, D. Rugg, D.E.J. Armstrong, M.P. Moody, P.A.J. Bagot, Scr. Mater., 185(2020), pp. 111-116.
[43]	W.F. Cui, H.R. Wei, G.Z. Luo, Q. Hong, L.A. Zhou, Rare Met. Mater. Eng., 26 (2)(1997), pp. 31-35.
[44]	A. Takasaki, K. Ojima, Y. Taneda, T. Hoshiya, A. Mitsuhashi, J. Mater. Sci., 28(1993), pp. 1067-1073.
[45]	R. Gaddam, B. Sefer, R. Pederson, Mater. Character., 99(2015), pp. 166-174.
[46]	A. Brotzu, F. Felli, D. Pilone, Intermetallics, 54(2014), pp. 176-180.
[47]	Ghonem.H Madsen. A, J. Mater. Eng. Perform., 4 (3)(1995), pp. 301-307.
[48]	G. Lütjering, S. Weissmann, Acta Mater, 18(1970), pp. 785-795.
[49]	C. Ramachandra, V. Singh, Scr. Mater., 20 (4)(1986), pp. 509-512.
[50]	A. Churchman, Pro. R. Soc. A, 226(1954), pp. 216-226
[51]	S. Djanarthany, J.C. Viala, J. Bouix, Mater. Chem. Phys., 72(2001), pp. 301-319.
[52]	W. Zhou, R. Sahara, K. Tsuchiya, J. Alloys Compd., 727(2017), pp. 579-595.
[53]	R.V. Ramanujan, P.J. Maziasz, C.T. Liu, Acta Mater, 44(1996), pp. 2611-2642.