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Acta Metall Sin  2016, Vol. 52 Issue (4): 455-462    DOI: 10.11900/0412.1961.2015.00399
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DEGENERATION PROCESS AND MECHANISM OF PRIMARY MC CARBIDES IN A CAST Ni-BASED SUPERALLOY
Wen SUN,Xuezhi QIN,Jianting GUO,Langhong LOU,Lanzhang ZHOU
Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
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Abstract  

Primary MC carbide is one of the most important phases in cast Ni-based superalloys. During long-term thermal exposure, the primary MC carbide is not stable and tends to degenerate, exhibiting various degeneration reactions, such as MC+γM6C+γ′, MC+γM6C + M23C6+ γ′ and MC+γM6C + M23C6+η. It is widely known that the degeneration of primary MC carbide has obvious influence on the microstructural evolutions of superalloys, including coarsening of γ′ phase, coarsening of grain boundaries and precipitation of topologically close-packed (TCP) phase, and consequently the mechanical properties of alloys. Much research work has focused on the degeneration mechanism of primary MC carbide during long-term thermal exposure, however, it is not very clear so far. In this work, a cast Ni-based superalloy is fabricated and thermally exposed at 850 ℃ for 500~10000 h in order to study the degeneration mechanism of primary MC carbide. The degeneration of primary MC carbide is observed by OM, SEM and TEM. High-angle annular dark field (HAADF) mode of TEM is used to clearly observe the degeneration of primary MC carbide and the element distribution in the degeneration areas. The results show that the primary MC degeneration is an inter-diffusion process which occurs between the primary carbide and the γ matrix. During the degeneration, C is released from the primary carbide, Ni, Al and Cr are provided by the γ matrix, while Ti, W and Mo come from both primary MC and γ matrix. The precipitation of η phase is determined by the atomic fraction of Ti+Nb+Ta+Hf and atomic ratio of (Ti+Nb+Ta+Hf)/Al and its amount is affected by the degeneration degree of primary MC carbide. The higher the degeneration degree, the larger the tendency for the precipitation of the η phase.

Key words:  cast Ni-based superalloy      long-term thermal exposure      primary MC carbide      degeneration mechanism     
Received:  17 July 2015     
Fund: Supported by National Natural Science Foundation of China (No.51001101) and National Energy Administration Program of China (No.NY20150102)

Cite this article: 

Wen SUN,Xuezhi QIN,Jianting GUO,Langhong LOU,Lanzhang ZHOU. DEGENERATION PROCESS AND MECHANISM OF PRIMARY MC CARBIDES IN A CAST Ni-BASED SUPERALLOY. Acta Metall Sin, 2016, 52(4): 455-462.

URL: 

https://www.ams.org.cn/EN/10.11900/0412.1961.2015.00399     OR     https://www.ams.org.cn/EN/Y2016/V52/I4/455

Fig.1  SEM image of primary MC carbide in alloy after heat treatment (a) and EPMA analysis of C (b), Ti (c), Nb (d), Mo (e), W (f), Cr (g), Al (h) and Ni (i)
Fig.2  SEM (a) and TEM (b) images of primary MC carbide in alloy after heat treatment (Inset in Fig.2b shows the SAED pattern)
Phase Cr Fe Ni Mo W Al Ti Nb
MC 2.6 - 5.0 13.6 31.1 - 43.0 4.7
γ' 9.9 11.7 67.1 0.9 2.0 2.4 6.1 -
M6C 12.7 10.0 15.1 24.4 37.8 - - -
M23C6 68.7 3.2 5.0 10.6 12.6 - - -
η 4.5 2.7 68.5 1.5 1.0 3.9 17.0 0.9
Table 1  Chemical compositions of phases in primary MC degeneration area (mass fraction / %)
Fig.3  BSE (a), TEM (b) and HAADF (c) images of primary MC carbide degeneration in alloy after thermally exposed at 850 ℃ for 1000 h and EDS analysis of M6C carbide (d) (Inset in Fig.3c shows the SAED pattern of M6C carbide)
Fig.4  BSE image of primary MC carbide in alloy after thermally exposed at 850 ℃ for 6000 h (a) and EPMA analysis of C (b), Ti (c), Nb (d), Cr (e) and Ni (f)
Fig.5  SEM (a) and HAADF (b) images of primary MC degeneration in alloy after thermally exposed at 850 ℃ for 10000 h and SAED patterns of γ' phase (c), M6C (d), M23C6 (e) and η phase (f) in the degeneration area
Fig.6  HAADF image of degenerating MC in Area 1 of Fig.5b (a) and distributions of elements C (b), Cr (c), W (d), Mo (e), Al (f), Ti (g) and Ni (h) in degeneration area (Arrows indicate the diffusion directions of various elements during degeneration)
Fig.7  HAADF image of degenerating MC in Area 2 of Fig.5b (a) and distributions of elements C (b), Cr (c), W (d), Mo (e) in degeneration area (Arrows indicate the diffusion directions of various elements during degeneration)
Alloy
Atomic fraction / % Atomic ratio of (Ti+Nb+Ta+Hf)/Al η phase precipitation D
Al Ti Nb Ta Hf Ti+Nb+Ta+Hf
K444 6.80 5.50 0.12 - 0.13 5.75 0.85 Yes High
K446 3.46 2.92 0.69 - - 3.61 1.04 No Low
K452 5.22 4.11 0.15 - - 4.26 0.82 Yes High
K465 11.89 3.41 0.69 - - 4.10 0.35 No Low
GTD-111 6.66 5.69 0.01 0.90 - 6.60 0.99 Yes High
IN738 7.32 3.91 0.74 0.38 - 5.03 0.69 Yes High
A0[20] 3.60 3.03 0.72 - - 3.75 1.04 No Low
Present alloy 3.92 4.23 0.06 - - 4.29 1.10 Yes High
A7[20] 4.12 4.15 0.07 - - 4.22 1.02 Yes High
A8[20] 3.88 4.04 0.07 - - 4.10 1.06 Yes High
Table 2  Relationship of chemical compositions with primary MC degeneration and η phase precipitation in Ni-based superalloys
[1] Tin S, Pollock T M.Mater Sci Eng, 2003; A348: 111
[2] Chen Q Z, Kong Y H, Jones C N, Knowles D M.Scr Mater, 2004; 51: 150
[3] Chen Q Z, Jones C N, Knowles D M.Scr Mater, 2002; 47: 669
[4] Bae J S, Lee J H, Kim S S, Jo C Y.Scr Mater, 2001; 45: 03
[5] Fernandaz R, Lecomte J C, Kattamis T E.Metall Trans, 1978; 91A: 381
[6] Liu L, Sommer F, Fu H Z.Scr Metall Mater, 1994; 30: 587
[7] Chen Q Z, Jones C N, Knowles D M.Acta Mater, 2002; 50: 1095
[8] Goswami T.Int J Fatigue, 1999; 21: 55
[9] Pedron J P, Pineau A.Mater Sci Eng, 1982; A56: 143
[10] Reuchet J, Remy L.Mater Sci Eng, 1983; A58: 33
[11] Wang J, Zhou L Z, Sheng L Y, Guo J T.Mater Des, 2012; 39: 55
[12] Collins H E.Trans ASM, 1969; 62: 82
[13] Wang J, Zhou L Z, Qin X Z, Sheng L Y, Hou J S, Guo J T.Mater Sci Eng, 2012; A533: 14
[14] Qin X Z, Guo J T, Yuan C, Hou J S, Ye H Q.Mater Sci Eng, 2012; A543: 121
[15] Qin X Z, Guo J T, Yuan C, Chen C L, Hou J S, Ye H Q.Mater Sci Eng, 2008; A485: 74
[16] Yang J X, Zheng Q, Sun X F, Guan H R, Hu Z Q.Mater Sci Eng, 2006; A429: 341
[17] Yang J X, Zheng Q, Sun X F, Guan H R, Hu Z Q.J Mater Sci, 2006; 41: 6476
[18] Choi B G, Kim I S, Kim D H, Jo C Y.Mater Sci Eng, 2008; A478: 329
[19] Lvov G, Levit V I, Kaufman M J.Mater Trans, 2004; 35A: 1669
[20] Sun W, Qin X Z, Guo Y A, Guo J T, Zhou L Z, Lou L H.Mater Des, 2015; 69: 81
[21] Liu L R, Jin T, Zhao N R, Wang Z H, Sun X F, Guan H R.Mater Sci Eng, 2003; A361: 191
[22] Koul A K, Castillo R.Metall Trans, 1988; 19A: 2049
[23] Sun W, Qin X Z, Guo Y A, Guo J T, Zhou L Z, Lou L H.Acta Metall Sin, 2014; 50: 744
[23] (孙文, 秦学智, 郭永安, 郭建亭, 周兰章, 楼琅洪. 金属学报, 2014; 50: 744)
[24] Zheng L, Cu C Q, Zheng Y R.Scr Mater, 2004; 50: 435
[25] Liu L R, Jin T, Zhao N R, Sun X F, Guan H R, Hu Z Q.Mater Lett, 2003; 57: 4540.
[26] Liu L R.PhD Dissertation, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, 2004
[26] (刘丽荣. 中国科学院金属研究所博士学位论文, 沈阳, 2004)
[27] Starink M J, Cama H, Thomson R C.Scr Mater, 1998; 38: 73
[28] Zheng L.Scr Mater, 2005; 53: 943
[29] Zheng Y R, Li S S, Zheng L, Han Y F.In: Reed R C, Green K A, Caron P, Gabb T P, Fahrmann M G, Huron E S, Woodard S A eds., Superalloys 2008, Warrendale: TMS, 2008: 743
[30] Watanabe M, Horita Z, Sano T, Nemoto M.Acta Metall, 1994; 42: 3381.
[31] Cui C Y, Gu Y F, Harada H, Ping D H, Sato A.Metall Mater Trans, 2006; 37A: 3183
[32] Cui C Y, Gu Y F, Harada H, Ping D H, Fukuda T.Mater Sci Eng, 2008; A485: 651
[33] Bouse G K.In: Kissinger R D, Deye D J, Anton D L, Cete A D, Nathal M V, Pollock T M, Woodford D A eds., Superalloys 1996,Warrendale: TMS, 1996: 163
[34] Seo S M, Kim I S, Lee J H, Jo C Y, Miyahara H, Ogi K.Metall Mater Trans, 2007; 38A: 883
[35] Wang J. Master Thesis, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, 2011
[35] (王建. 中国科学院金属研究所硕士学位论文, 沈阳, 2011)
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