EFFECT OF EXTENT OF HOMOGENIZATION ON THE HOT DEFORMATION RECRYSTALLIZATION OF SUPERALLOY INGOT IN COGGING PROCESS
Jianxin DONG(),Linhan LI,Haoyu LI,Maicang ZHANG,Zhihao YAO
School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083
Cite this article:
Jianxin DONG,Linhan LI,Haoyu LI,Maicang ZHANG,Zhihao YAO. EFFECT OF EXTENT OF HOMOGENIZATION ON THE HOT DEFORMATION RECRYSTALLIZATION OF SUPERALLOY INGOT IN COGGING PROCESS. Acta Metall Sin, 2015, 51(10): 1207-1218.
The elimination of the segregation improves the thermo plasticity of superalloy ingot during the homogenization process, but coarser grain structure and high-temperature oxidation caused in further homogenization have an adverse impact on the thermo plasticity. The inheritance of coarse grain structure in the followed hot working process increases the tendency of cogging crack and makes the grain refining harder, leading to a lower yield of the final workpiece. The microstructure characteristics and their hot deformation behaviors of GH4740H, GH4738, GH3625 and 690 alloys under different homogenizations were investigated by means of microstructure analysis methods and crack propagation testing. The experimental results show that the reasonable homogenization processing needs to take into account the segregation elimination arising thermo plasticity addition, more to consider grain coarsing and severe oxidation leading to decrease plasticity. Based on the residue dendrites can provide more recrystalazation nucleation sites, the partial homogenization possessing probably exists rationality. This research work provides an exploratory study for the improvement of the homogenization-cogging process of superalloy.
Fig.1 Microstructure of dendrite at R/2 of as-cast 690 alloy ingot
Fig.2 Changes of segregation index and grain size with time of 690 alloy during homogenization treatment
Fig.3 Crack growth rate curves of 690 alloy under different homogenizations (da/dN—crack growth rate, DK—intensity factor range)
Fig.4 Fatigue fracture morphologies of 690 alloy under homogenization at 1150 ℃ for 60 h (a), 1180 ℃ for 30 h (b, c), and 1240 ℃ for 30 h (d)
Fig.5 Microstructure of dendrite at R/2 of as-cast GH4740H ingot
Fig.6 Cross-sectional microstructures of GH4740H alloy under homogenization at 1110 ℃ for 8 h (a) and 24 h (b)
Fig.7 Cross-sectional SEM image (a) and EDS mapping analysis of rectangular area in Fig.7a (b~d) of GH4740H alloy under homogenization at 1110 ℃ for 48 h
Fig.8 Cross-sectional microstructures of GH4740H alloy under homogenization at 1170 ℃ for 8 h (a) and 48 h (b)
Fig.9 Thicknesses of oxidized area of GH4740H alloy under homogenization at 1170 ℃ for different times
Fig.10 Microstructures of as-cast GH3625 alloy (a), and soaking at 1250 ℃ for 5 min (b), hot compressed at 1100 ℃, 0.01 s-1, 50% (c)
Fig.11 Segregation index of Cr, Mo and Nb in GH3625 alloy at different states
Fig.12 SEM image (a) and EDS mapping analysis of Cr, Mo and Nb distributions (b~d) of hot compressed GH3625 alloy
Fig.13 Microstructures of as-cast GH4738 alloy (a) and under homogenization at 1150 ℃ for 12 h (b), 24 h (c) and 50 h (d)
Fig.14 True stress-true strain curves of hot compressed (1150 ℃, 0.1 s-1, 30%) GH4738 alloy under different homogenizations
Fig.15 Metallographies of the center area samples after hot compression (1150 ℃, 0.1 s-1, 30%) of as-cast GH4738 alloy (a) and homogenized at 1150 ℃ for 12 h (b), 24 h (c) and 50 h (d)
Fig.16 Recrystallization positions of as-cast GH4738 alloy after hot compression in small deformation zone (a) and large deformation zone (b) (A, B, C show recrystallization site near carbide particles)
Fig.17 FESEM images of the center area of as-cast GH4738 alloy (a) and homogenized at 1150 ℃ for 12 h after hot compression (1150 ℃, 0.1 s-1, 30%) (b)
Fig.18 Microstructure of the center area of as-cast GH4738 alloy after hot compression
Area
As-cast
Homogenized 3 h
Homogenized 12 h
Center
1.852
1.677
1.193
Edge
2.079
1.864
1.323
Table 2 Segregation index of Ti in different status
Fig.19 Schematics of microstructure evolution of as-homogenized (a) and as-partially homogenized (b) alloy before and after hot deformation
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