Hot Deformation Characteristics of Novel Wrought Superalloy GH4975 Extruded Rod Used for 850 ℃ Turbine Disc
ZHANG Yong1(), LI Xinxu1, WEI Kang1, WAN Zhipeng1, JIA Chonglin1, WANG Tao1, LI Zhao1, SUN Yu2, LIANG Hongyan3
1 Key Laboratory of Science & Technology on Advanced High Temperature Structural Materials, AECC Beijing Institute of Aeronautical Materials, Beijing 100095, China 2 School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China 3 School of Materials Science and Engineering, Tianjin University, Tianjin 300354, China
Cite this article:
ZHANG Yong, LI Xinxu, WEI Kang, WAN Zhipeng, JIA Chonglin, WANG Tao, LI Zhao, SUN Yu, LIANG Hongyan. Hot Deformation Characteristics of Novel Wrought Superalloy GH4975 Extruded Rod Used for 850 ℃ Turbine Disc. Acta Metall Sin, 2020, 56(10): 1401-1410.
With the development of aero-engine in the direction of high thrust ratio, high efficiency and high reliability, the indicators of temperature resistance of cast & wrought superalloys are getting higher and higher. For the demand of aero-engine, the wrought superalloy materials used for aero engine turbine disc have been made remarkable progress. Form heat-resistant steel which temperature capability reaches 550 ℃ to iron-nickel based superalloy used at 650 ℃, and the high alloyed wrought superalloy with service temperature of 750 ℃ have been developed. The nickel-based wrought superalloy GH4975 is a high strength, complex alloying, hard-deformed wrought turbine disc alloy, which can be used at 850 ℃. In the study, the thermal deformation behavior of GH4975 extruded rod prepared by vacuum induction melting (VIM) and vacuum arc remelting (VAR) was studied by thermal simulation machine with the temperature range of 1070~1220 ℃ and strain rate range of 0.001~1 s-1. The results show that the stress-strain curves of GH4975 alloy are divided into three stages: strain hardening, flow softening and steady state rheology, exhibiting typical dynamic recrystallization characteristics. The constitutive equation of GH4975 extruded rod was established and the hot deformation activation energy was calculated as 664587 J/mol. Besides, the processing maps of GH4975 alloy were drawn based on the dynamic material model (DMM), and the suitable processing parameters are determined by combining with microstructure observation. The dynamic recrystallization easily occurs at the deformation temperature range of 1100~1130 ℃, and the nucleation mechanisms were elaborated to be strain inducing grain boundary.
Fig.1 Microstructures of GH4975 alloy bar corroded after extrusion and recrystallization(a) OM image(b) SEM image(c) prime γ' phase
Fig.2 True stress-true strain curves of GH4975 superalloy obtained under deformation temperatures of 1070 ℃ (a), 1100 ℃ (b), 1130 ℃ (c), 1150 ℃ (d), 1180 ℃ (e) and 1220 ℃ (f) at different strain rates
Fig.3 Relationships between ln and lnσ (a), ln and σ (b), ln and ln[sinh(ασ)] (c), ln[sinh(ασ)] and 1000/T (d), lnZ and ln[sinh(ασ)] (e) (—strain rate; σ—stress; α, β and A—material constants; Z—Zener-Hollomon parameter; T—temperature; n and n1—stress exponents; r2—correlation coefficient)
Fig.4 Comparison between the experimental values and predicted values by Arrhenius model
Fig.5 Processing map of GH4975 superalloy at the strain of 0.8 (Gray area represents instability region) and microstructure validation of different deformation region (Contour value is powder dissipation rate)
Fig.6 Effect of deformation temperature on the microstructures of GH4975 superalloy under the strain rate of 0.1 s-1(a) 1070 ℃ (b) 1100 ℃ (c) 1130 ℃ (d) 1150 ℃ (e) 1180 ℃ (f) 1220 ℃
Fig.7 Effect of strain rate on the microstructures of GH4975 superalloy under a certain temperature of 1130 ℃ (a) 1 s-1 (b) 0.1 s-1 (c) 0.01 s-1 (d) 0.001 s-1
Fig.8 TEM images of microstructures of GH4975 superalloy deformed at 1150 ℃, 0.001 s-1 (a), 1180 ℃, 0.1 s-1 (c) and 1180 ℃, 1 s-1 (d); Hereinto, Fig.8b is the selected area electron diffraction pattern (SAEDP) of Fig.8a, which is to identify the γ′ precipitates
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