A new type-γ′/γ′′ coprecipitation behavior and its evolution mechanism in wrought Ni-based ATI 718Plus superalloy

doi:10.1016/j.jmst.2021.12.033

Abstract

Abstract:

In the precipitation-hardened Ni-based superalloy, typified by ATI 718Plus, the nano-scale γ′ and γ′′ phase in duplet or triple coprecipitate morphology can provide superior high-temperature strength. Thus, it is of great sense to study the evolution of γ′/γ′′ coprecipitate during long term service at elevated temperature. In this study, the new-type γ′/γ′′ coprecipitates with a sandwich or compact configuration were found firstly in wrought ATI 718Plus superalloy during long term thermal exposure at 705 °C. These co-structure of the γ′/γ′′ precipitates evidently inhibit the coarsening of γ′ phase. The increase of thermal exposure time evidently leads to the increase of the volume fraction of γ′/γ′′ coprecipitate and transformation of sandwich-type γ′/γ′′ coprecipitate to compact-type γ′/γ′′ coprecipitate, which is characterized as γ′′ phase precipitate at several faces of the γ′ phase. The main evolution mechanism of γ′/γ′′ coprecipitates is element segregation, especially the composition variations of Al + Ti and Nb and their ratio of Al+Ti/Nb. In addition, the interfacial energy between γ′′ phase and γ matrix also plays a key role on the γ′/γ′′ coprecipitates evolution. The calculated results show that the longer thermal exposure time leads to the higher interfacial energy, which is beneficial for nucleation and precipitation of γ′′ phase on the faces of γ′ phase.

Key words: Wrought 718Plus superalloy, γ′/γ′′ coprecipitates, Long-term thermal exposure, Precipitate evolution

Qianying Guo, Zongqing Ma, Zhixia Qiao, Chong Li, Teng Zhang, Jun Li, Chenxi Liu, Yongchang Liu. A new type-γ′/γ′′ coprecipitation behavior and its evolution mechanism in wrought Ni-based ATI 718Plus superalloy[J]. J. Mater. Sci. Technol., 2022, 119: 98-110.

Figures/Tables 19

Table 1. Chemical composition of the explored ATI 718Plus superalloy (wt.%) [3].

Ni	Cr	Co	Fe	Nb	Mo	Al	Ti	W	C	P	B
51.73	18.53	9.26	8.82	5.34	2.85	1.55	0.8	1.08	0.024	0.011	0.007

Fig. 1. Schematic diagram of long-term thermal exposure heat treatment used in this study.

Fig. 2. SEM images of initial microstructure: (a) γ′ phases, (b) η phases, (c) BF-STEM image of γ′ phases and the corresponding EDS mapping results.

Fig. 3. Low and high magnification SEM images of γ′/γ′′ coprecipitates after long-term thermal exposure at 705 °C for (a) and (e) 100 h, (b) and (f) 200 h, (c) and (g) 500 h, (d) and (h) 1000 h; (i) and (j) The schematic models of sandwich-type γ′/γ′′ coprecipitate and compact-type γ′/γ′′ coprecipitate.

Fig. 4. Quantitative analysis of γ′ phases after long-term thermal exposure: (a) the size distribution histograms, (b) average size and volume fraction, (c) coarsening behavior according to LSW model and (d) the plot between log (rt) / log (r0) and log t.

Table 2. Specific data of volume fraction and average size of γ′ phases in four 718Plus samples after LTTE heat treatments.

Samples	Volume fraction (%)	Average size (nm)
100-LTTE	33.5 ± 1.1	66.6 ± 4.3
200-LTTE	35.4 ± 1.3	68.4 ± 2.0
500-LTTE	38.1 ± 1.6	69.9 ± 1.1
1000-LTTE	40.3 ± 0.9	72.6 ± 0.5

Fig. 5. The microstructure of 705-100 sample: (a) and (b) low and high dark-field TEM (DF-TEM) images showing the γ′ phases. (c) SAED pattern of γ′ phase and (d) bright-field TEM (BF-TEM) image and the corresponding EDS result (the insert). (e) high resolution TEM (HRTEM) images of (e1) γ′ phase and (e2) γ matrix, (f) HAADF-STEM image of γ′ phases and the corresponding EDS mapping results.

Fig. 6. The microstructure of 705-200 sample: (a) and (b) low and high DF-TEM images showing the γ′ phases. (c) SAED pattern of γ′ phase and (d) BF-TEM image and the corresponding EDS result (the insert). (e) HRTEM images of (e1) γ′ phase and (e2) γ matrix, (f) HAADF-STEM image of γ′ phases and the corresponding EDS line-scan results: (f1) Ni, Al, Ti, Nb and (f2) Cr, Fe, Co.

Fig. 7. The microstructure of 705-500 sample: (a) and (b) low and high resolution DF-TEM images showing the γ′ phases (the phases circled by blue oval are γ′′ phases). (c) SAED pattern of γ′ phase and (d) BF-TEM image (the phases circled by blue oval are γ′′ phases) and the corresponding EDS result (the insert). (e) and (f) HRTEM images and the corresponding FFT patterns of γ matrix, γ′ phase and γ′′ phase. (g) HAADF-STEM image of γ′ and γ′′ phases and the corresponding EDS line-scan results: (g1) Ni, Al, Ti, Nb and (g2) Cr, Fe, Co.

Fig. 8. The microstructure of 705-1000 sample: (a) and (b) low and high resolution DF-TEM images showing the γ′ phases (the phases circled by blue oval are γ′′ phases). (c) SAED pattern of γ′ phase and (d) BF-TEM image (the phases circled by blue oval are γ′′ phases) and the corresponding EDS result (the insert). (e) HRTEM image of γ′ and γ′′ phase, (f) HAADF-STEM image of γ′ and γ′′ phases and the corresponding EDS mapping results, (g) HAADF-STEM image and EDS line-scan profile of (g1) Ni, Al, Ti, Nb and (g2) Cr, Fe, Co.

Table 3. The average chemical composition (at. %) of γ′ phase in four 718Plus samples after LTTE heat treatments.

Sample	Ni	Cr	Co	Fe	Al	Ti	Nb
100-LTTE	69.79 ± 0.78	2.35 ± 0.01	3.83 ± 0.92	1.60 ± 0.15	4.98 ± 0.51	3.50 ± 0.09	14.07 ± 0.28
200-LTTE	74.13 ± 0.08	1.33 ± 0.05	3.57 ± 0.20	1.67 ± 0.17	5.39 ± 0.05	2.75 ± 0.09	11.13 ± 0.12
500-LTTE	72.42 ± 0.17	1.82 ± 0.16	4.24 ± 0.38	1.79 ± 0.08	5.03 ± 0.06	2.72 ± 0.43	11.96 ± 0.07
1000-LTTE	73.38 ± 0.35	1.19 ± 0.14	4.13 ± 0.12	1.72 ± 0.12	4.56 ± 0.04	3.07 ± 0.14	12.10 ± 0.14

Table 4. Specific data of average size and aspect ratio of γ′′ phases in four 718Plus samples after LTTE heat treatments.

Samples	Average size (nm)		Aspect ratio
Samples	Length	Width	Aspect ratio
100-LTTE	36.1 ± 0.1	5.0 ± 0.8	0.19 ± 0.01
200-LTTE	43.4 ± 0.4	16.9 ± 0.6	0.39 ± 0.02
500-LTTE	46.4 ± 0.2	16.1 ± 2.3	0.36 ± 0.05
1000-LTTE	47.6 ± 2.9	6.9 ± 0.7	0.15 ± 0.02

Fig. 9. The Gaussian fitting results of diffraction peaks (111) of (a) 100-LTTE, (b) 200-LTTE, (c) 500-LTTE and (d) 1000-LTTE samples.

Table 5. Lattice parameters of the γ and γ′ and the γ/γ′ misfits of four 718Plus samples after LTTE heat treatments.

Sample	100-LTTE	200-LTTE	500-LTTE	1000-LTTE
a_γ (nm)	0.2247	0.2247	0.2248	0.2249
a_γ' (nm)	0.2248	0.2249	0.2251	0.2254
δ (%)	0.04 %	0.1 %	0.13 %	0.22 %

Table 6. The interfacial energy between γ matrix and γ′ phase calculated using Ti diffusion (σTi diffusion) and Al diffusion (σAl diffusion).

Sample	100-LTTE	200-LTTE	500-LTTE	1000-LTTE
σ_{Ti diffusion} (mJ/m²)	2.0	0.98	0.68	1.74
σ_{Al diffusion} (mJ/m²)	3.64	3.87	5.15	2.61

Table 7. The chemical compositions (at.%) of γ′ phase and γ matrix and associated partition coefficient values of four 718Plus samples after LTTE heat treatments, as obtained from TEM-EDS.

Empty Cell	100-LTTE			200-LTTE			500-LTTE			1000-LTTE
Empty Cell	γ'	γ	k_i	γ'	γ	k_i	γ'	γ	k_i	γ'	γ	k_i
Ni	69.76	53.43	1.31	71.87	53.02	1.36	70.51	53.03	1.33	72.39	53.61	1.35
Cr	2.62	18.86	0.14	1.44	18.90	0.08	2.17	18.92	0.11	1.16	18.46	0.06
Co	2.86	12.03	0.24	3.63	12.10	0.30	4.48	12.16	0.37	3.82	12.09	0.32
Fe	1.81	9.44	0.19	1.86	9.52	0.20	1.92	9.62	0.20	1.65	9.26	0.18
Al	9.61	1.79	5.37	11.26	1.96	5.74	10.81	1.76	6.14	9.67	1.97	4.91
Ti	4.35	0.61	7.13	3.17	0.69	4.59	2.74	0.71	3.86	3.85	0.75	5.13
Nb	8.99	3.12	2.88	6.75	2.39	2.82	7.33	2.38	3.08	7.42	2.57	2.89

Fig. 10. (a) The histograms of partition coefficient (Ki) of the solute element (i) in four 705-LTTE samples, (b) the relations between [Ci(alloy)-Ci(γ)] and [Ci(γ′)-Ci(γ)] calculating the volume fraction of γ′ phase, (c) the comparison plot between the volume fractions of γ′ phase calculated from TEM-EDS analysis using the mass balance-based lever rule and statistically analyzed from SEM images.

Fig. 11. HAADF-STEM images showing the γ'/γ'' coprecipitates after LTTE at 705 °C for (a) 100 h, (b) 200 h, (c) 500 h and (d) 1000 h.

Fig. 12. A qualitative model schematic illustration directly showing the evolution of γ′/γ′′ coprecipitates: (a) all evolution process during 705-LTTE heat treatment, (b) the evolution from γ′ to γ′′/γ′/γ′′ “sandwich coprecipitates, (c) the evolution from γ′′/γ′/γ′′ “sandwich” coprecipitates to γ′/γ′′ “partly compact” coprecipitates, (d) the evolution from γ′′/γ′/γ′′ “sandwich coprecipitates and γ′/γ′′ “partly compact” coprecipitates to γ′/γ′′ “all compact” coprecipitates.

References 42

[1]	G. Asala, A.K. Khan, J. Andersson, O.A. Ojo, Metall. Mater. Trans. A 48 (2017) 4211-4228. DOI URL
[2]	G. Asala, J. Andersson, O.A. Ojo, Int. J. Adv. Manuf. Technol. 87 (2016) 2721-2729. DOI URL
[3]	J. Li, Y.T. Wu, Y.C. Liu, C. Li, Z.Q. Ma, L.M. Yu, H.J. Li, C.X. Liu, Q.Y. Guo, Mater. Charact. 169 (2020) 110547. DOI URL
[4]	P.R. Yang, C.X. Liu, Q.Y. Guo, Y.C. Liu, J. Mater. Sci. Technol. 21 (2021) 162-171.
[5]	S. Meher, S. Nag, J. Tiley, A. Goel, R. Banerjee, Acta Mater 61 (2013) 4266-4276. DOI URL
[6]	R.P. Shi, D.P. McAllister, N. Zhou, A.J. Detor, R. DiDomizio, M.J. Mills, Y.Z. Wang, Acta Mater 164 (2019) 220-236. DOI URL
[7]	A.J. Detor, R. DiDomizio, R. Sharghi-Moshtaghin, N. Zhou, R.P. Shi, Y.Z. Wang, D.P. McAllister, M.J. Mills, Metall. Mater. Trans. A 49 (2018) 708-717. DOI URL
[8]	Y.N. Zhao, Q.Y. Guo, Z.Q. Ma, L.Q. Yu, Mater. Sci. Eng. A 791 (2020) 139735. DOI URL
[9]	F. Theska, K. Nomoto, F. Godor, B. Oberwinkler, A. Stanojevic, S.P. Ringer, S. Primig, Acta Mater 188 (2020) 492-503. DOI URL
[10]	F. Theska, A. Stanojevic, B. Oberwinkler, S. Primig, Mater. Sci. Eng. A 776 (2020) 138967. DOI URL
[11]	S.A. Mantri, S. Dasari, A. Sharma, T. Alam, M.V. Pantawane, M. Pole, S. Sharma, N.B. Dahotre, R. Banerjee, S. Banerjee, Acta Mater 210 (2021) 116844. DOI URL
[12]	Z. Qiao, C. Li, H.J. Zhang, H.Y. Liang, Y.C. Liu, Y. Zhang, Int. J. Miner. Metall. Mater. 27 (2020) 1123-1131. DOI URL
[13]	G. Asala, J. Andersson, O.A. Ojo, Corros. Sci. 158 (2019) 108086. DOI URL
[14]	F. Theska, A. Stanojevic, B. Oberwinkler, S.P. Ringer, S. Primig, Acta Mater 156 (2018) 116-124. DOI URL
[15]	P. Pandey, S. Kashyap, D. Palanisamy, A. Sharma, K. Chattopadhyay, Acta Mater 177 (2019) 82-95. DOI URL
[16]	P. Pandey, A.K. Sawant, B. Nithin, Z. Peng, S.K. Makineni, B. Gault, K. Chattopad- hyay, Acta Mater 168 (2019) 37-51. DOI
[17]	S. Mukhopadhyay, P. Pandey, B. Nithin, K. Biswas, S.K. Makineni, K. Chattopad- hyay, Acta Mater 208 (2021) 116736. DOI URL
[18]	H.J. Zhang, C. Li, Y.C. Liu, Q.Y. Guo, H.J. Li, Mater. Sci. Eng. A 677 (2016) 515-521. DOI URL
[19]	P. Zhang, Y. Yuan, L. Zhong, Y.F. Gu, J.B. Yan, J.T. Lu, Z. Yang, Materialia 16 (2021) 101061. DOI URL
[20]	L. Luo, Y. Ma, S.S. Li, Y.L. Pei, L. Qin, S.K. Gong, Intermetallics 99 (2018) 18-26. DOI URL
[21]	Q.Z. Gao, Y.J. Jiang, Z.Y. Liu, H.L. Zhang, C.C. Jiang, X. Zhang, H.J. Li, Mater. Sci. Eng. A 779 (2020) 139139. DOI URL
[22]	L. Tang, J.J. Liang, C.Y. Cui, J.G. Li, Y.Z. Zhou, X.F. Sun, Y.T. Ding, Mater. Sci. Eng. A 786 (2020) 139438. DOI URL
[23]	X. He, C. Liu, Y.K. Yang, J. Ding, X.G. Chen, X.C. Xia, Y. Tang, Y.C. Liu, J. Alloy. Compd. 872 (2021) 159674. DOI URL
[24]	Y.T. Wu, C. Li, X.C. Xia, H.Y. Liang, Q.Q. Qi, Y.C. Liu, J. Mater. Sci. Technol. 67 (2021) 95-104. DOI URL
[25]	X.L. Zhuang, S. Antonov, L.F. Li, Q. Feng, Scr. Mater. 202 (2021) 114004. DOI URL
[26]	S. Meher, M.C. Carroll, T.M. Pollock, L.J. Carroll, Mater. Des. 140 (2018) 249-256. DOI URL
[27]	J.C. Zhang, T.W. Huang, F. Lu, K.L. Cao, D. Wang, J. Zhang, J. Zhang, H.J. Su, L. Liu, Scr. Mater. 204 (2021) 114131. DOI URL
[28]	T.J. Zhou, H.S. Ding, X.P. Ma, W. Feng, H.B. Zhao, Y. Meng, H.X. Zhang, Y.M. Lv, Mater. Sci. Eng. A 725 (2018) 299-308. DOI URL
[29]	C. Ai, X.B. Zhao, J. Zhou, H. Zhang, L. Liu, Y.L. Pei, S.S. Li, S.K. Gong, J. Alloy. Compd. 632 (2015) 558-562. DOI URL
[30]	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
[31]	H. Jiang, C. Liu, J.X. Dong, M.C. Zhang, J. Alloy. Compd. 821 (2020) 153217. DOI URL
[32]	D.J. Sauza, D.C. Dunand, R.D. Noebe, D.N. Seidman, Acta Mater 164 (2019) 654-662. DOI URL
[33]	E.A. Lass, D.J. Sauza, D.C. Dunand, D.N. Seidman, Acta Mater 147 (2018) 284-295. DOI URL
[34]	N. Baler, P. Pandey, D. Palanisamy, S.K. Makineni, G. Phanikumar, K. Chattopad- hyay, Materialia 10 (2020) 100632. DOI URL
[35]	P. Pandey, A. Raj, N. Baler, K. Chattopadhyay, Materialia 16 (2021) 101072. DOI URL
[36]	F.L.R. Tirado, S. Taylor, D.C. Dunand, Acta Mater 172 (2019) 44-54. DOI URL
[37]	Y.C. Chen, C.P. Wang, J.J. Ruan, T. Omori, R. Kainuma, K. Ishida, X.J. Liu, Acta Mater 170 (2019) 62-74. DOI URL
[38]	Y. Guan, Y.C. Liu, Z.Q. Ma, H.J. Li, H.Y. Yu, J. Alloy. Compd. 842 (2020) 155891. DOI URL
[39]	J.C. Zhang, T.W. Huang, F. Lu, K.L. Cao, D. Wang, J. Zhang, J. Zhang, H.J. Su, L. Liu, J. Alloy. Compd. 876 (2021) 160114. DOI URL
[40]	X.G. You, Y. Tan, H.Y. Cui, H.X. Zhang, X.P. Zhuang, L.H. Zhao, S.Q. Niu, Y. Li, P.T. Li, Mater. Charac. 173 (2021) 110925. DOI URL
[41]	R.V. Patil, G.B. Kale, J. Nucl. Mater. 230 (1996) 57-60. DOI URL
[42]	M. Rafiei, H. Mirzadeh, M. Malekan, M.J. Sohrabi, J. Alloy. Compd. 793 (2019) 277-282. DOI URL