Effect of grain boundary precipitates on the stress rupture properties of K4750 alloy after long-term aging at 750 °C for 8000 h

doi:10.1016/j.jmst.2021.03.022

Abstract

Abstract:

In K4750 alloy, the evolution of grain boundary (GB) precipitates, including the degradation of blocky MC carbide particles and the precipitation of granular/needle-like η phase particles, were observed after long-term aging (LA) at 750°C for 8000 h. During MC degradation, the Ti and C released from the MC carbide combined with Ni and Cr, respectively, in the γ matrix to form η-Ni₃Ti phase and Cr-rich M₂₃C₆ carbide. Large amounts of granular η phase precipitated at GBs and the needle-like η phase grew gradually from GBs toward the grain interior. Because of the growth of the η phase through absorbing γ′ phase, γ′-depleted zones were formed around the η phase. The evolution of the MC carbide and η phase was primarily responsible for the decrease of the stress rupture life and the increase of elongation. After an LA sample was tested at 750°C and 360 MPa, the residual strain distribution was investigated by electron backscatter diffraction (EBSD). The results showed that the residual strain mainly distributed at GBs, especially in the region of MC degradation and at the edges of η phases, which was closely related to the appearance of phase interfaces. Microvoids/cracks easily initiated at phase interfaces, then easily extended along the γ′-depleted zones, thus the stress rupture life of LA samples was substantially shorter than that of samples subjected to the standard treatment. In particular, because of large amounts of fine degraded MC, granular M₂₃C₆ and granular η phase particles distributed at GBs after 750°C /8000 h LA and microvoid/crack formation could be hindered by the formation of dimples, which led to an increase of elongation.

Key words: Ni-base superalloy, Long-term aging, MC carbide, η phase, Stress rupture properties, Residual strain distribution

Meiqiong Ou, Yingche Ma, Kunlei Hou, Min Wang, Guangcai Ma, Kui Liu. Effect of grain boundary precipitates on the stress rupture properties of K4750 alloy after long-term aging at 750 °C for 8000 h[J]. J. Mater. Sci. Technol., 2021, 92: 11-20.

Figures/Tables 12

Fig. 1. SEM images showing (a-c) the MC and M23C6 carbides in specimen subjected to ST, (d-f) the η phase, MC carbide and M23C6 carbide in specimen subjected to 750°C/8000 h LA, and the γ′ phase in specimens subjected to (g) ST or (h) 750°C/8000 h LA.

Fig. 2. (a) SEM image of precipitates in specimen subjected to 750°C/8000 h LA, EDS line-scanning analysis results show the variation of (b) Ni, (c) Ti, (d) Cr, and (e) Nb contents in the precipitates.

Fig. 3. TEM morphology, EDS spectrum and inset selected area electron diffraction (SEAD) patterns of the precipitates in specimens subjected to (a, b) ST or (c-e) 750°C/8000 h LA.

Table 1 The chemical composition (wt.%) of the metal clusters (M) in the M23C6 and MC carbides, and the chemical composition (wt.%) of η phase after the ST or the 750°C/8000 h LA treatment.

Mark in Fig. 3	phases	Heat treatment	Ni	Cr	Fe	W	Mo	Ti	A l	Nb
a1	M₂₃C₆	ST	7.5	81.3	0.4	5.8	5.0	-	-	-
b1	MC	ST	1.5	1.2	-	4.9	2.4	28.4	-	61.6
c1	η	LA	72.6	3.6	1.4	5.0	1.0	8.6	1.3	6.5
c2	M₂₃C₆	LA	5.2	69.1	0.5	20.6	4.2	0.2	0.2	-
e2	MC	LA	1.3	2.2	0.1	24.5	5.1	26.5	-	40.2

Fig. 4. (a) TEM image, and the corresponding EDS mapping images show the distribution of (b) Ni, (c) Cr, (d) Fe, (e) W, (f) Al, (g) Ti, (h) Nb, (i) Mo and (j) C elements in specimen subjected to 750°C/8000 h LA treatment.

Table 2 Stress rupture properties of the K4750 alloy after the ST or the 750°C/8000 h LA treatment.

Heat treatment	Test condition	Stress rupture life	Elongaiton
ST	750°C/430 MPa	164.2 h	10.5%
ST	750°C/360 MPa	475.6 h	5.0%
LA	750°C/430 MPa	20.1 h	15.5%
LA	750°C/360 MPa	138.3 h	13.0%

Fig. 5. (a, b) Orowan looping mechanism in the ST specimen after testing at 750°C/430 MPa, the stacking fault (SF) shearing mechanism in the LA specimens after testing at (c, d) 750°C/430 MPa and (e, f) 750°C/ 360 MPa.

Fig. 6. The longitudinal microstructures and fracture surfaces of (a-c) 750°C/430 MPa stress rupture specimen subjected to the ST, (d-f) 750°C/430 MPa and (g-i) 750°C/360 MPa stress rupture specimens subjected to the 750°C/8000 h LA treatment.

Fig. 7. The longitudinal microstructures of 750°C/360 MPa stress rupture specimen subjected to 750°C/8000 h LA. (a, b) SEM images showing GB microvoids/cracks, (c) BSE image distinguishing GBs precipitates, (d) SEM image showing the propagation of microvoids/cracks along needle-like η phase.

Fig. 8. EDS maps showing the distribution of (a) Ni, (b) Cr, (c) Fe, (d) W, (e) Al, (f) Ti, (g) Nb, (h) Mo, and (i) C elements, (j) the band contract map, and (k) the phase map in 750°C/360 MPa stress rupture specimen subjected to the 750°C/8000 h LA treatment.

Fig. 9. (a) The band contract map, (b) the phase map, and the IPFs of (c) γ matrix, (d) η phase, (e) M23C6 carbide and (f) MC carbide along Z0 direction in 750°C/360 MPa stress rupture specimen subjected to the 750°C/8000 h LA treatment.

Fig. 10. (a) The phase map, the KAM distribution maps of (b) all phases, (c) γ matrix, (d) η phase, (e) M23C6 carbide, and (f) MC carbide in 750°C/360 MPa stress rupture specimen subjected to the 750°C/8000 h LA treatment.

References 43

[1]	R.C. Reed, The Superslloys: Fundamentals and Applications, Cambridge Univer-sity Press, New York, 2006.
[2]	T.M. Pollock, S. Tin, J. Propul. Power 22 (2006) 361-374. DOI URL
[3]	A. Picasso, A. Somoza, A. Tolley, J. Alloys Compd. 479 (2009) 129-133. DOI URL
[4]	M.Q. Ou, Y.C. Ma, H.L. Ge, B. Chen, S.J. Zheng, K. Liu, Mater. Sci. Eng. A 736 (2018) 76-86. DOI URL
[5]	H. Jiang, J. Dong, M. Zhang, J. Alloys Compd. 782 (2019) 323-333. DOI URL
[6]	X.Z. Qin, J.T. Guo, C. Yuan, C.L. Chen, J.S. Hou, H.Q. Ye, Mater. Sci. Eng. A 485 (2008) 74-79. DOI URL
[7]	S. Antonov, J. Huo, Q. Feng, D. Isheim, D.N. Seidman, R.C. Helmink, E. Sun, S. Tin, Mater. Sci. Eng. A 687 (2017) 232-240. DOI URL
[8]	J.P. Shingledecker, G.M. Pharr, Metall. Mater. Trans. A 43 (2012) 1902-1910. DOI URL
[9]	M.R. Jahangiri, M. Abedini, Mater. Des. 64 (2014) 588-600. DOI URL
[10]	C.N. Wei, H.Y. Bor, L. Chang, J. Alloys Compd. 509 (2011) 5708-5714. DOI URL
[11]	B. Tian, C. Lind, O. Paris, Mater. Sci. Eng. A 358 (2003) 44-51. DOI URL
[12]	P. Kontis, A. Kostka, D. Raabe, B. Gault, Acta Mater 166 (2019) 158-167. DOI URL
[13]	G. Bai, J. Li, R. Hu, T. Zhang, H. Kou, H. Fu, Mater. Sci. Eng. A 528 (2011) 2339-2344. DOI URL
[14]	G. Lvov, V.I. Levit, M.J. Kaufman, Metall. Mater. Trans. A 35 (2004) 1669-1679. DOI URL
[15]	Q. Li, S. Tian, H. Yu, N. Tian, Y. Su, Y. Li, Mater. Sci. Eng. A 633 (2015) 20-27. DOI URL
[16]	J. Yang, Q. Zheng, M. Ji, X. Sun, Z. Hu, Mater. Sci. Eng. A 528 (2011) 1534-1539. DOI URL
[17]	K. Zhao, Y.H. Ma, L.H. Lou, J. Alloys Compd. 475 (2009) 648-651. DOI URL
[18]	N. D’Souza, B. Kantor, G.D. West, L.M. Feitosa, H.B. Dong, J. Alloys Compd. 702 (2017) 6-12. DOI URL
[19]	J.X. Yang, Q. Zheng, X.F. Sun, H.R. Guan, Z.Q. Hu, J. Mater. Sci. 41 (2006) 6476-6478. DOI URL
[20]	Y.S. Lim, D.J. Kim, S.S. Hwang, H.P. Kim, S.W. Kim, Mater. Charact. 96 (2014) 28-39. DOI URL
[21]	M.Q. Ou, X.C. Hao, Y.C. Ma, R.C. Liu, L. Zhang, K. Liu, J. Alloys Compd. 732 (2018) 107-115. DOI URL
[22]	P. Kontis, D.M. Collins, R.C. Reed, A.J. Wilkinson, D. Raabe, B. Gault, Scr. Mater. 147 (2018) 59-63. DOI URL
[23]	W. Sun, X. Qin, J. Guo, L. Lou, L. Zhou, Mater. Des. 69 (2015) 81-88. DOI URL
[24]	X. Chen, Z. Yao, J. Dong, H. Shen, Y. Wang, J. Alloys Compd. 735 (2018) 928-937. DOI URL
[25]	G Liu, X.S Xiao, M. Véron, S. Birosca, Acta Mater 185 (2020) 493-506. DOI URL
[26]	J. Wang, L.Z. Zhou, L.Y. Sheng, J.T. Guo, Mater. Des. 39 (2012) 55-62. DOI URL
[27]	R.C. Reed, T. Tao, N. Warnken, Acta Mater 57 (2009) 5898-5913. DOI URL
[28]	M. Anderson, A.L. Thielin, F. Bridiera, P. Bocher, J. Savoie, Mater. Sci. Eng. A 679 (2017) 48-55. DOI URL
[29]	F. Long, Y.S. Yoo, C.Y. Jo, S.M. Seo, Y.S. Song, T. Jin, Z.Q. Hu, Mater. Sci. Eng. A 527 (2009) 361-369. DOI URL
[30]	K.J. Ducki, M. Hetmanczyk, D. Kuc, Mater. Chem. Phys. 81 (2003) 490-492. DOI URL
[31]	S. Antonov, M. Detrois, R.C. Helmink, S. Tin, J. Alloys Compd. 626 (2015) 76-86. DOI URL
[32]	C.S. Wang, T.T. Wang, M.L. Tan, Y.G. Guo, J.T. Guo, L.Z. Zhou, J. Mater. Sci. Technol. 31 (2015) 135-142. DOI URL
[33]	M.Q. Ou, Y.C. Ma, H.L. Ge, W.W. Xing, Y.T. Zhou, S.J. Zheng, K. Liu, J. Alloys Compd. 735 (2018) 193-201. DOI URL
[34]	B. Alabbad, S. Tin, Mater. Charact. 151 (2019) 53-63. DOI
[35]	T.M. Smith, B.D. Esser, N. Antolin, G.B. Viswanathan, T. Hanlon, A. Wessman, D. Mourer, W. Windl, D.W. McComb, M.J. Mills, Acta Mater. 100 (2015) 19-31. DOI URL
[36]	M.Q. Ou, Y.C. Ma, W.W. Xing, X.C. Hao, B. Chen, L.L. Ding, K. Liu, J. Mater. Sci. Technol. 35 (2019) 1270-1277. DOI URL
[37]	K.L. Hou, M.Q. Ou, M. Wang, H.Z. Li, Y.C. Ma, Kui Liu, Mater. Sci. Eng. A 763 (2019) 138137. DOI URL
[38]	D.L. Shu, S.G. Tian, N. Tian, J. Xie, Y. Su, Mater. Sci. Eng. A 700 (2017) 152-161. DOI URL
[39]	F. Sun, Y.F. Gu, J.B. Yan, Z.H. Zhong, M. Yuyama, Acta Mater. 102 (2016) 70-78. DOI URL
[40]	G.B. Viswanathan, P.M. Sarosi, M.F. Henry, D.D. Whitis, W.W. Milligan, M.J. Mills, Acta Mater. 53 (2005) 3041-3057. DOI URL
[41]	R.R. Unocic, N. Zhou, L. Kovarik, C. Shen, Y. Wang, M.J. Mills, Acta Mater. 59 (2011) 7325-7339. DOI URL
[42]	B.D. Fu, K. Du, G.M. Han, C.Y. Cui, J.X. Zhang, Mater. Lett. 152 (2015) 272-275. DOI URL
[43]	X. Li, J. Zhang, L. Rong, Y. Li, Mater. Sci. Eng. A 488 (2008) 547-553. DOI URL