The newly developed high-performance cast-wrought alloys have been widely applied in advanced turbine engines in recent years, particularly, served as turbine disc and compressor disc. The significant breakthrough has been made on the processing techniques for these highly alloyed disc alloys, including the triple-melting of the large-scale ingots with the diameter more than 500 mm, conversion of the large-scale ingot and the processing of fine-grained billets with the diameter more than 300 mm, customization of the microstructures and properties of disc forgings. The chemical compositions can be well controlled on vacuum arc remelting (VAR) ingots, including the ultra-low carbon content lower than 0.011%. The white spots and freckles have been found to be the primary defects on large-scale VAR ingots, which is triggered by the improper re-melting parameters. The metallurgical defects can be identified on fine-grained billets via supersonic inspection. The investigations have shown that the existence of the micro-duplex structure opens a window for the processing of these highly alloyed disc alloys with up to more than 60% mass fraction of precipitates. Via a multicycle thermal-mechanical processing technique, the hot working process of the disc alloys, can be achieved in a cost-effective way, and the un-recrystallized grains can also be eliminated efficiently. The above-mentioned techniques have greatly promoted the development and application of the high-performance disc alloys, such as GH4065, GH4720, GH4175 and GH4975, et al. These alloys can provide a promising solution of high reliability combined with low life cycle cost for military and commercial gas turbines. Nonetheless, in order to maximize the advantageous of cast-wrought disc alloys on reliability and cost-effective ratio, the comprehensive understanding about the prevention and identification of metallurgical defects, increase in the yield rate of materials during conversion, processing of fine-grained billets and dual-property disc forgings, is still needed.
Fig.1 Development of cast-wrought disc superalloys abroad
Alloy
Mass fraction of
Mass fraction of γ′
γ-γ′ mismatch at 760 ℃
γ′ solvus temperature
Al+Ti+Nb / %
at 760 ℃ / %
%
℃
GH4586
5.0
29
-0.355
1072
GH4742
7.8
37
+0.273
1095
GH4065
6.6
36
-0.016
1113
GH4079
8.5
46
+0.131
1132
GH4720
7.5
43
+0.088
1158
GH4156
9.0
53
+0.003
1165
GH4151
9.9
54
-0.128
1171
GH4175
11.0
55
-0.080
1176
GH4975
9.2
64
-0.079
1210
Table 1 Characteristic parameters of highly alloyed cast-wrought disc alloys[3,4,5,8,14,23,24,25,26,27,28]
Fig.2 Relationship between stress rupture property and the concentration of alloying elements of disc alloys
Fig.3 Relationship between formation temperature of MC carbides and C content in alloy GH4065(a) phase diagram (b) details of MC carbides formation temperature
Fig.4 Schematic of standard processing route of cast-wrought disc forgings and associated key techniques (VIM—vacuum induction melting, ESR—electroslag remelting, VAR—vacuum arc remelting)
Fig.5 Clean white spot identified on a GH4586 disc forging produced via double-melting technique(a) macro-scale morphology (b) optical image
Fig.7 Coarse-grained macrostructures on billet induced by improper conversion techniques(a) low-magnification (b) residual as-cast structures
Fig.8 Super-plasticity of γ+γ' microduplex of disc alloys with various γ' mass fractions (deformed at the temperature of 100 ℃ lower than γ' solvus temperature and the strain rate of 1×10-3 s-1)
Fig.6 A freckle identified on the billet of alloy GH4065 with diameter of 300 mm(a~c) macro-scale morphologies of the freckle under various conditions of incident light ((a, b) transverse, (c)longitudinal)(d~h) EPMA mappings of alloying elements distribution
Fig.9 Numerical simulation of the trigger and growth of freckles during the VAR re-melting process (f—solid fraction in mushy zone)(a) f map (b, c) solute distribution (d) macro-scale flow pattern of liquid phase in the mushy zone
Fig.10 Morphological evolution of freckles during conversion and their supersonic identification on GH4065 billets(a) a freckle in coarse-grained structure(b, c) morphologies of the freckle in γ+γ' microduplex(d) C-scan plot showing a freckle on fine-grained billet indicated by arrow (Color scale is for C-scan map)
Fig.11 Discrete dirty white spot on GH4065 disc forging identified by supersonic inspection(a) macro-scale morphology of white spot (blue arrow) and stringers (red arrows)(b) optical image of stringers (indicated by red arrows in Fig.11a)(c) C-scan plot showing a defect on disc forging(d~k) EPMA analyses identified the stringer as inclusions
Fig.12 Interaction between dislocations and γ' precipitates during hot working process of disc alloys(a) dens dislocations induced by strain ageing effect in alloy GH4586(b) low dislocation density in γ+γ' microduplex in alloy GH4065(c) HRTEM image of γ-γ' interface in Fig.12b
Fig.13 Special γ-γ' configurations developed during hot working process of alloy GH4065 due to the mechanism of strain induced discontinuous precipitation of γ' phase(a) original structure in single austenite region(b) fine and dispersed γ' precipitate during deformation in two-phase region(c, d) optical and SEM images of discontinuous precipitated γ', respectively(e, f) EBSD phase map and low angle misorientation (5°), respectively
Fig.14 Hot working plasticity of alloy GH4065 characterized by percent area reduction of tension tests(a) as-cast structures after solutioning treatment (b) γ+γ' microduplex (c) schematic of original specimen
Fig.15 Morphologies of γ+γ' microduplex of disc alloys with various γ' mass fractions during superplastic deformation at the temperature of 100 ℃ lower than γ' solvus temperature (given in Table 1) and strain rate of 1×10-3 s-1(a) GH4065 (b) GH4720 (c) GH4175 (d) GH4975
Fig.16 Large-scale disc forgings and the macrostructural homogeneity of alloy GH4065(a) compressor blisk and low-pressure turbine disc(b) macrostructure of disc forging
Fig.17 As-solutioning microstructures of the full-scale disc forgings optical images of alloy GH4065 (a, b) and GH4175 (c), TEM image of dislocation free γ+γ' microduplex in Fig.17a (d), TEM images of small un-recrystallized grains indicated by arrows in Fig.17b (e, f)
[1]
ReedR C. The Superalloys: Fundamentals and Applications [M]. Cambridge: Cambridge University Press, 2006: 236
[2]
DonachieM J, DonachieS J. Superalloys: A Technical Guide [M]. 2nd Ed., Ohio: ASM International, 2002: 120
[3]
ShiC X, ZhongZ Y. Forty years of superalloy R & D in China [J]. Acta Metall. Sin., 1997, 33: 1
[3]
师昌绪, 仲增墉. 中国高温合金40年 [J]. 金属学报, 1997, 33: 1
[4]
JiangH F. Requirements and forecast of turbine disk materials [J]. Gas Turb. Exp. Res., 2002, 15(4): 1
[4]
江和甫. 对涡轮盘材料的需求及展望 [J]. 燃气涡轮试验与研究, 2002, 15(4): 1)
[5]
WangX D, WangH C. Improved development superalloys, promote the aero-engine development [A]. The Thirteenth Session of the Annual China Superalloys Conference [C]. Beijing: Metallurgical Industry Press, 2015: 3
SimsC T, StoloffN S, HagelW C. Superalloys II—High Temperature Materials for Aerospace and Industrial Power [M]. New York: John Wiley & Sons, 1987: 32
[7]
DevauxA, GeorgesE, HéritierP. Development of new C&W superalloys for high temperature disk applications [J]. Adv. Mater. Res., 2011, 278: 405
[8]
High Temperature Material Branch of the Chinese Society for Metals. China Superalloys Handbook (Volume One) [M]. Beijing: China Standards Press, 2012: 891
WilliamsJ C, Starke JrE A. Progress in structural materials for aerospace systems [J]. Acta Mater., 2003, 51: 5775
[10]
FangB, JiZ, LiuM, , et al. Study on constitutive relationships and processing maps for FGH96 alloy during two-pass hot deformation [J]. Mater. Sci. Eng., 2014, A590: 255
[11]
CarterJ L W, KuperM W, UchicM D, , et al. Characterization of localized deformation near grain boundaries of superalloy René-104 at elevated temperature [J]. Mater. Sci. Eng., 2014, A605: 127
[12]
FindleyK O, SaxenaA. Low cycle fatigue in René 88DT at 650 ℃: Crack nucleation mechanisms and modeling [J]. Metall. Mater. Trans., 2006, 37A: 1469
[13]
ViswanathanG B, SarosiP M, HenryM F, , et al. Investigation of creep deformation mechanisms at intermediate temperatures in René 88 DT [J]. Acta Mater., 2005, 53: 3041
[14]
HuangQ Y, LiH K. Superalloy [M]. Beijing: Metallurgical Industry Press, 2000: 385
[14]
黄乾尧, 李汉康. 高温合金 [M]. 北京: 冶金工业出版社, 2000: 385)
[15]
DeckerR F. The evolution of wrought age-hardenable superalloys [J]. JOM, 2006, 58(9): 32
[16]
PreliF R, FurrerD. Lessons learned from the development, application and advancement of alloy 718 [A]. 8th International Symposium on Superalloy 718 and Derivatives [C]. Pittsburgh: TMS, 2014: 3
[17]
HayesR W, UnocicR R, NasrollahzadehM. Creep deformation of allvac 718Plus [J]. Metall. Mater. Trans., 2015, 46A: 218
[18]
LiuY C, ZhangH J, GuoQ Y, , et al. Microstructure evolution of Inconel 718 superalloy during hot working and its recent development tendency [J]. Acta Metall. Sin., 2018, 54: 1653
DevauxA, PicquéB, GervaisM F, , et al. AD730TM—A new nickel-based superalloy for high temperature engine rotative parts [A]. Superalloys 2012 [C]. Warrendale, PA: TMS, 2012: 911
[20]
CrozetC, DevauxA, ForestierR, , et al. Effect of ingot size on microstructure and properties of the new advanced AD730TM superalloy [A]. Superalloys 2016 [C]. Warrendale, PA: TMS, 2016: 437
[21]
HeaneyJ A, LasondeM L, PowellA M, , et al. Development of a new cast and wrought alloy (René 65) for high temperature disk applications [A]. 8th International Symposium on Superalloy 718 and Derivatives [C]. Pittsburgh: TMS, 2014: 67
[22]
ReedR C, MotturaA, CruddenD J. Alloys-by-design: Towards optimization of compositions of nickel-based superalloys [A]. Superalloys 2016 [C]. Warrendale, PA: TMS, 2016: 15
[23]
ShiC X, ZhongZ Y. Development and innovation of superalloy in China [J]. Acta Metall. Sin., 2010, 46: 1281
[23]
师昌绪, 仲增墉. 我国高温合金的发展与创新 [J]. 金属学报, 2010, 46: 1281
[24]
LongZ D, ZhuangJ Y, DengB, , et al. A new method to improve the hot workability of high strength Ni-based superalloys [J]. Acta Metall. Sin., 1999, 35: 1211
DongJ X, LiL H, LiH Y, , et al. Effect of extent of homogenization on the hot deformation recrystallization of superalloy ingot in cogging process [J]. Acta Metall. Sin., 2015, 51: 1207
ZhangB J, ZhaoG P, ZhangW Y, , et al. Investigation of high performance disc alloy GH4065 and associated advanced processing techniques [J]. Acta Metall. Sin., 2015, 51: 1227
GenereuxP D, BorgC A. Characterization of freckles in a high strength wrought nickel superalloy [A]. Superalloys 2000 [C]. Warrendale, PA: TMS, 2000: 19
[34]
CharpagneM A, CharpagneM A, BillotT, , et al. Heteroepitaxial recrystallization observed in René 65TM and Udimet 720TM: A new recrystallization mechanism possibly occurring in all low lattice mismatch γ-γ' superalloys? [A]. Superalloys 2016 [C]. Warrendale, PA: TMS, 2016: 417
[35]
AndrewW, AudeL, AudeL, , et al. Thermal stability of cast and wrought alloy Rene 65 [A]. Superalloys 2016 [C]. Warrendale, PA: TMS, 2016: 793
[36]
WlodekS T, KellyM, AldenD A. The structure of René 88 DT [A]. Superalloys 1996 [C]. Warrendale, PA: TMS, 1996: 129
[37]
BryantD J, McIntoshD G. The manufacture and evaluation of a large turbine disc in cast and wrought alloy 720Li [A]. Superalloys 1996 [C]. Warrendale, PA: TMS, 1996: 713
[38]
ZhangB J, ZhaoG P, JiaoL Y, , et al. Influence of hot working process on microstructures of superalloy GH4586 [J]. Acta Metall. Sin., 2005, 41: 351
ZhangJ, HuangT W, LiuL, , et al. Advances in solidification characteristics and typical casting defects in nickel-based single crystal superalloys [J]. Acta Metall. Sin., 2015, 51: 1163
BondB J, O'BrienC M, RussellJ L, , et al. René 65 billet material for forged turbine components [A]. 8th International Symposium on Superalloy 718 and Derivatives [C]. Pittsburgh: TMS, 2014: 107
[49]
LarrouyB, VillechaiseP, CormierJ, , et al. Influence of both temperature and γ' distribution on the development of strain incompatibilities at grain boundaries at low temperature in the UdimetTM 720 Li superalloy [A]. 8th International Symposium on Superalloy 718 and Derivatives [C]. Pittsburgh: TMS, 2014: 713
[50]
ValitovV A. Formation of nanocrystalline structure upon severe thermomechanical processing and its effect on the superplastic properties of nickel base alloys [A]. 8th International Symposium on Superalloy 718 and Derivatives [C]. Pittsburgh: TMS, 2014: 739
[51]
TileyJ, ViswanathanG B, SrinivasanR, , et al. Coarsening kinetics of γ' precipitates in the commercial nickel base Superalloy René 88 DT [J]. Acta Mater., 2009, 57: 2538
[52]
MacSleyneJ, UchicM D, SimmonsJ P, , et al. Three-dimensional analysis of secondary γ' precipitates in René-88 DT and UMF-20 superalloys [J]. Acta Mater., 2009, 57: 6251
[53]
RadisR, SchafferM, AlbuM, , et al. Multimodal size distributions of γ' precipitates during continuous cooling of UDIMET 720 Li [J]. Acta Mater., 2009, 57: 5739
