Effect of boron addition on the microstructure and mechanical properties of K4750 nickel-based superalloy

doi:10.1016/j.jmst.2020.02.079

Abstract

Abstract:

The effect of boron addition at 0, 0.007 wt. % and 0.010 wt. % on the microstructure and mechanical properties of K4750 nickel-based superalloy was studied. The microstructure of the as-cast and heat-treated alloys was analyzed by SEM, EPMA, SIMS and TEM. Lamellar M₅B₃-type borides were observed in boron-containing as-cast alloys. After the full heat treatment, boron atoms released from the decomposition of M₅B₃ borides were segregated at grain boundaries, which inhibited the growth and agglomeration of M₂₃C₆ carbides. Therefore, the M₂₃C₆ carbides along grain boundaries were granular in boron-containing alloys, while those were continuous in boron-free alloys. The mechanical property analysis indicated that the addition of boron significantly improved the tensile ductility at room temperature and stress rupture properties at 750 ℃/430 MPa of K4750 alloy. The low tensile ductility at room temperature of 0B alloy was attributed to continuous M₂₃C₆ carbides leaded to stress concentration, which provided a favorable location for crack nucleation and propagation. The improvement of the stress rupture properties of boron-containing alloys was the result of the combination of boron segregation increased the cohesion of grain boundaries and granular M₂₃C₆ carbides suppressed the link-up and extension of micro-cracks.

Key words: Nickel-based superalloy, Boron addition, Secondary ion mass spectrometry (SIMS), Grain boundary segregation, Mechanical properties

Xiaoxiao Li, Meiqiong Ou, Min Wang, Long Zhang, Yingche Ma, Kui Liu. Effect of boron addition on the microstructure and mechanical properties of K4750 nickel-based superalloy[J]. J. Mater. Sci. Technol., 2021, 60: 177-185.

Figures/Tables 14

Table 1 The measured chemical composition of three experimental alloys (wt. %).

	B	C	Cr	Mo	Al	Ti	Nb	W	Fe	Ni
Alloy 1	0	0.12	19.23	1.50	1.23	2.97	1.51	2.87	4.57	balance
Alloy 2	0.007	0.12	19.19	1.38	1.23	2.95	1.50	2.90	4.52	balance
Alloy 3	0.010	0.12	19.32	1.50	1.22	2.97	1.51	2.81	4.58	balance

Fig. 1. SEM images showing the microstructure of three as-cast alloys: (a and d) 0B, (b and e) 0.007 wt. % B, (c and f) 0.010 wt. % B.

Fig. 2. (a) TEM image, (b) selected area diffraction pattern and (c) EDS spectra of MC carbides in 0B as-cast alloy.

Fig. 3. EPMA analysis of 0.007 wt. % B as-cast alloy: (a) secondary electron image, (b) C-map, (c) B-map, (d) Cr-map and 0.010 wt. % B ac-cast alloy: (e) secondary electron image, (f) C-map, (g) B-map, (h) Cr-map.

Fig. 4. (a and b) TEM images of borides in 0.010 wt. % B as-cast alloy; (c) selected area diffraction pattern and (d) EDS spectra of M5B3.

Table 2 The chemical composition of M5B3 in 0.010 wt. % B as-cast alloy.

Element	Al	W	Ti	Cr	Fe	Ni	Nb	Mo
wt. %	0.1	30.7	0.2	60.2	0.6	2.2	0.4	5.5
at. %	0.4	11.6	0.3	80.0	0.8	2.6	0.3	4.0

Fig. 5. SEM images of (a-f) carbides morphology and (g-i) γ′ distribution in heat-treated alloys: (a, d, and g) 0B alloy, (b, e, and h) 0.007 wt. % B alloy, (c, f, and i) 0.010 wt. % B alloy.

Fig. 6. (a) TEM image of M23C6 carbides along GB in 0.010 wt. % B heat-treated alloy, (b) selected area diffraction pattern and (c) EDS spectra of M23C6; (d) SIMS image and (e) B-map of 0.010 wt. % B heat-treated alloy, (f) the distribution of B at GB.

Table 3 The chemical composition of M23C6 carbide in 0.010 wt. % B heat-treated alloy.

Element	C	Al	W	Ti	Cr	Fe	Ni	Mo
wt.%	6.9	0.2	17.8	0.2	62.0	0.9	5.6	6.4
at.%	27.9	0.3	4.7	0.2	58.1	0.8	4.7	3.2

Fig. 7. Decomposition process of the lamellar borides in 0.010 wt. % B as-cast alloy during heat treatment at 1150 ℃ for (a) 0 min, (b) 5 min and (c) 15 min.

Fig. 8. Engineering stress vs. engineering strain curves of heat-treated alloys with different boron content at room temperature.

Fig. 9. SEM images of tensile fracture surfaces at room temperature: (a) 0B, (b) 0.007 wt. % B, (c) 0.010 wt. % B; the longitudinal microstructure of (d and e) 0B heat-treated alloy after tensile testing at room temperature; (f) TEM image of M23C6 carbide in 0B heat-treated alloy.

Fig. 10. (a) The stress rupture life and (b) the stress rupture ductility of three alloys at 750 ℃/430 MPa.

Fig. 11. The fracture surfaces and the longitudinal microstructures of (a, d, and g) 0B, (b, e, and h) 0.007 wt. % B, (c, f, and i) 0.010 wt. % B alloys after stress rupture testing at 750 ℃/430 MPa.

References 45

[1]	T.J. Garosshen, T.D. Tillman, G.P. McCarthy, Metall. Mater. Trans. A 18 (1987) 69-77.
[2]	E.S. Huron, K.R. Bain, D.P. Mourer, J.J. Schirra, P.L. Reynolds, E.E. Montero, in: K.A. Green, T.M. Pollock, H. Harada, T.E. Howson, R.C. Reed, J.J. Schirra, S. Walston (Eds.), Proc. Int. Symp. Superalloys, 2004, pp. 73-81.
[3]	D. Blavette, P. Caron, T. Khan, Scr. Mater. 20(1986) 1395-1400.
[4]	C.S. Wang, Y.A. Guo, J.T. Guo, L.Z. Zhou, Mater. Sci. Eng. A 639 (2015) 380-388.
[5]	C.T. Liu, C.L. White, J.A. Horton, Acta Metall 33 (1985) 213-229.
[6]	T. Takasugi, O. Izumi, Acta Metall 33 (1985) 1247-1258.
[7]	Y. Liu, K.Y. Chen, G. Lu, J.H. Zhang, Z.Q. Hu, Acta Mater. 45(1997) 1837-1849.
[8]	J.X. Yang, Q. Zheng, X.F. Sun, H.R. Guan, Z.Q. Hu, Mater. Sci. Eng. A 429 (2006) 341-347.
[9]	K. Laha, J. Kyono, T. Sasaki, S. Kishimoto, N. Shinya, Metall. Mater. Trans. A 36 (2005) 399-409.
[10]	K. Laha, J. Kyono, N. Shinya 56 (2007) 915-918.
[11]	P.J. Zhou, J.J. Yu, X.F. Sun, H.R. Guan, Z.Q. Hu, Mater. Sci. Eng. A 491 (2008) 159-163. DOI URL
[12]	C.S. Lee, G.W. Han, R.E. Smallman, D. Feng, J.K.L. Lai, Acta Metall 47 (1999) 1823-1830.
[13]	A.P. Sutton, R.W. Ballufﬁ, New York, 1995. URL PMID
[14]	D. Raabe, M. Herbig, S. Sandlobes, Y. Li, D. Tytko, M. Kuzmina, D. Ponge, P.P. Choi, Curr. Opin. Solid State Mat. Sci. 18(2014) 253-261. DOI URL
[15]	H.R. Zhang, O.A. Ojo, M.C. Chaturvedi, Scr. Mater. 58(2008) 167-170.
[16]	O.A. Ojo, H.R. Zhang, Metall. Mater. Trans. A 39 (2008) 2799-2803.
[17]	H.R. Zhang, O.A. Ojo, J. Mater. Sci. 43(2008) 6024-6028.
[18]	O.A. Ojo, H.R. Zhang, Philos. Mag. Abingdon (Abingdon) 90(2010) 765-782.
[19]	B.P. Wu, L.H. Li, J.T. Wu, Z. Wang, Y.B. Wang, X.F. Chen, J.X. Dong, J.T. Li, Int. J. Miner. Metall. Mater. 21(2014) 1120-1126.
[20]	Y.L. Cai, Y.R. Zheng, Metallographic Study of Superalloys, National Defence Industry Press, 1966.
[21]	X. Huang, M.C. Chaturvedi, N.L. Richards, J. Jackman, Acta Mater. 45(1997) 3095-3107.
[22]	B.C. Yan, J. Zhang, L.H. Lou, Mater. Sci. Eng. A 474 (2008) 39-47.
[23]	B.N. Du, L.Y. Sheng, C.Y. Cui, J.X. Yang, X.F. Sun, Mater. Charact. 128(2017) 109-114.
[24]	P. Kontis, H.A. Mohd Yusof, S. Pedrazzini, M. Danaie, K.L. Moore, P.A.J. Bagot, M. P. Moody, C.R.M. Grovenor, R.C. Reed, Acta Mater. 103(2016) 688-699.
[25]	M.Q. Ou, Y.C. Ma, X.C. Hao, B.F. Wan, T. Liang, K. Liu, J. Mater. Sci. Technol. 33(2017) 1300-1307. DOI URL
[26]	X.C. Hao, L. Zhang, X. Zhao, T. Liang, Y.C. Ma, K. Liu, Mater. Sci. Forum 816 (2015) 586-593.
[27]	M.A. Burke, J. Greggi, G.A. Whitlow, Scr. Metall. Mater. 18(1984) 91-94.
[28]	C.L. White, J.H. Schneibel, R.A. Padgett, Metall. Mater. Trans. A 14 (1983) 595-610.
[29]	M. McLean, A. Strang, Met. Technol. 11(1984) 454-464. DOI URL
[30]	B. Tian, C. Lind, O. Paris, Mater. Sci. Eng. A 358 (2003) 44-51.
[31]	Y.S. Lim, D.J. Kim, S.S. Hwang, H.P. Kim, S.W. Kim, Mater. Charact. 96(2014) 28-39. DOI URL
[32]	C.N. Wei, H.Y. Bor, L. Chang, J. Alloys. Compd. 509(2011) 5708-5714.
[33]	M. Kurban, U. Erb, K.T. Aust, Scr. Mater. 54(2006) 1053-1058.
[34]	X.B. Hu, Y.L. Zhu, N.C. Sheng, X.L. Ma, Sci. Rep. 4(2014) 7367. DOI URL PMID
[35]	X.B. Hu, Y.L. Zhu, X.H. Shao, H.Y. Niu, L.Z. Zhou, X.L. Ma, Acta Mater. 100(2015) 64-72.
[36]	F. Yang, J.S. Hou, S. Gao, C.S. Wang, L.Z. Zhou, Mater. Sci. Eng. A 715 (2018) 126-136.
[37]	C.L. Briant, Embrittlement of Engineering Alloys, Elsevier, 2013.
[38]	F. Sun, Y.F. Gu, J.B. Yan, Y.X. Xu, Z.H. Zhong, M. Yuyama, J. Alloys. Compd. 687(2016) 389-401.
[39]	D. Wu, T.T. Yao, D.Z. Li, S.P. Lua, Mater. Sci. Eng. A 731 (2018) 21-28.
[40]	J.T. Guo, H. Li, C. Sun, S.H. Wang, D.G. Ren, L.Y. Xiong, J. Jiang, Mater. Sci. Eng. A 152 (1992) 120-125. DOI URL
[41]	S. Dryepondt, D. Monceau, F. Crabos, C. Vernault, Mater. Sci. Forum, Trans. Tech. Publ. 461-464(2004) 647-654.
[42]	R. Jiang, N. Gao, P. Reed, J. Mater. Sci. 50(2015) 4379-4386. DOI URL
[43]	F.W. Kang, J.F. Sun, G.Q. Zhang, Z. Li, H.F. Ao, J. Shen, Rare Met. Mater. Eng. 36(2007) 1205-1209.
[44]	J.X. Yang, Q. Zheng, X.F. Sun, H.R. Guan, Z.Q. Hu, Mater. Sci. Eng. A 429 (2006) 341-347.
[45]	X.Z. Qin, J.T. Guo, C. Yuan, J.S. Hou, L.Z. Zhou, H.Q. Ye, Mater. Sci. Eng. A 543 (2012) 121-128.