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Acta Metall Sin  2025, Vol. 61 Issue (11): 1653-1663    DOI: 10.11900/0412.1961.2024.00028
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Analyses of As-Cast Microstructure and Cracking Sensitivity of GH4151 Wrought Superalloy with High γ′ Phase Content
ZHONG Jia, WANG Fa, JIANG He, YAO Zhihao, DONG Jianxin()
School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China
Cite this article: 

ZHONG Jia, WANG Fa, JIANG He, YAO Zhihao, DONG Jianxin. Analyses of As-Cast Microstructure and Cracking Sensitivity of GH4151 Wrought Superalloy with High γ′ Phase Content. Acta Metall Sin, 2025, 61(11): 1653-1663.

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Abstract  

Nickel-based superalloys, known for their excellent high-temperature mechanical characteristics and structural stability, are extensively utilized in critical high-temperature components of gas turbine engines, including combustion chambers, turbine blades, and turbine disks. With the development of aeronautical technology, the required maximum operating temperature of turbine disks is 800 oC and above. To meet such high-temperature application requirements, China designed GH4151, a new type of nickel-based wrought superalloy that contains precipitation strengthening elements such as Al, Nb, and Ti along with solid solution strengthening elements such as Cr, Co, Mo, and W. The weight ratio of the solid solution strengthening elements was 34% and that of the precipitation strengthening elements was 10%. Due to the high alloying degree of GH4151 wrought superalloy, its smelting process often results in solute distribution and element segregation between liquid and solid phases, which can lead to the precipitation of numerous harmful phases during solidification, causing cracks in the ingot. Subsequent processing becomes impossible once cracks appear. To study the cast microstructure complexity and its correlation with ingot cracking, the elemental segregation, cast microstructure, phase precipitation behavior, and cracking characteristics of GH4151 wrought superalloy were analyzed by OM, SEM, DSC, extraction phase analysis, XRD, hot compression simulation, and thermodynamic calculations. The results indicated that Nb segregation in GH4151 ingots was severe, with a segregation coefficient as high as 2.3. Elemental segregation in the alloy led to the precipitation of various phases, including massive γ′ phases, Laves phases, MC carbides, γ/γ′ eutectic phases, and η phases. The γ′ phase, Laves phase, and MC carbide structures are Ni2.42Co0.40Cr0.10Mo0.04W0.03Ti0.26Al0.59Nb0.12V0.03, (Co0.241Cr0.205Ni0.554)2(Nb0.309Mo0.242Ti0.346W0.102), and (Ti0.333Nb0.521Mo0.100W0.028V0.019)C, respectively. Due to elemental segregation, numerous precipitated phases with coarse sizes and irregular morphologies formed during solidification. The GH4151 ingot was highly susceptible to cracking, with potential crack formation at the interface of complex precipitates between dendrites, namely Laves phases, γ/γ′ eutectic phases, MC carbides, η phases, and the matrix. A high γ′ phase content of 41.177% in GH4151 reduced its thermal conductivity and increased the likelihood of thermal stress accumulation during cooling, ultimately leading to increased cracking sensitivity in the alloy ingot due to a combination of solidification segregation and thermal stress accumulation.

Key words:  GH4151 wrought superalloy      as-cast microstructure      element segregation      crack analysis     
Received:  29 January 2024     
ZTFLH:  TG115.23  
Fund: National Science and Technology Major Projects(J2019-VI-0021-0137)
Corresponding Authors:  DONG Jianxin, professor, Tel: (010)62332884, E-mail: jxdong@ustb.edu.cn

URL: 

https://www.ams.org.cn/EN/10.11900/0412.1961.2024.00028     OR     https://www.ams.org.cn/EN/Y2025/V61/I11/1653

Fig.1  OM images showing the dendritic morphologies in different regions of GH4151 alloy consumable ingot with a diameter of 410 mm
(a) edge region
(b) 1/2 radius region
(c) center region
RegionPrimary dendrite arm spacing / μmSecondary dendrite arm spacing / μmSegregation coefficient
AlTiVCrCoNbMoW
Edge146.982.60.81.01.11.01.01.81.31.1
1/2 radius381.7112.70.91.30.80.90.92.31.21.0
Center496.9133.00.91.60.71.01.02.31.30.6
Table 1  Dendrite arm spacings and element segregation coefficients in different regions of GH4151 alloy consumable ingot
Fig.2  Thermodynamic calculation results of GH4151 alloy based on JMatPro software
(a) element segregation behavior
(b) equilibrium phase diagram (Inset shows the full view of phase diagram)
Fig.3  SEM images of as-cast microstructure of GH4151 alloy consumable ingot with a diameter of 410 mm
(a) Laves phase and η phase
(b) petal shaped γ/γ′ eutectic phase
(c) MC carbides
PhaseCAlTiVCrCoNiNbMoW
Laves1.21.60.421.122.225.312.213.72.3
η6.58.13.612.661.06.51.20.5
γ/γ′ eutectic9.77.33.012.763.13.11.00.1
MC56.30.110.80.30.30.41.628.90.80.5
Table 2  Chemical compositions of interdendritic precipitates in as-cast GH4151 alloy
Fig.4  SEM images of γ′ phase in different regions of GH4151 alloy consumable ingot with a diameter of 410 mm
(a) interdendritic (b) dendrite core
Fig.5  XRD spectra of precipitated phase powders extracted from GH4151 alloy
(a) γ' phase (b) MC carbides, Laves phase, and η phase
PhaseNiCNbTiAlCoCrMoWVTotal
γ26.282-2.1252.2992.9454.3410.9890.7401.1820.274041.177
Laves0.055-0.0260.015-0.0240.0180.0210.017-0.176
MC-0.0380.1520.050---0.0300.0160.00300.289
Table 3  Chemical compsitions and fractions of phases in GH4151 alloy consumable ingot with a diameter of 410 mm
Fig.6  Heating and cooling DSC curves of GH4151 alloy at the rate of 10 oC/min
Fig.7  Solidification path of GH4151 alloy calculated based on JMatPro software

Phase

JMatPro valueHeating temperature pointCooling temperature point
Liquid132613251315
Solid126712491308
MC129512901254
η1160-1163
γ117511501112, 1163
γ/γ-11501130
Laves1095-1090
Table 4  Phase transition temperatures of GH4151 alloy during solidification
Fig.8  Schematic of solidification process of GH4151 alloy
Fig.9  Macro-morphology of cracked surface (a) and SEM images of different phase interfaces (b-e) of GH4151 alloy consumable ingot with a diameter of 410 mm after isothermal hot compression test at 1120 oC with strain rate of 1 s-1 and deformation of 30% (DRX—dynamic recrystallization)
(b) MC/γ phase interface (c) Laves phase interface
(d) γ/γ′ eutectic phase interface (e) η phase interface
Fig.10  SEM images of the crack zone morphology of GH4151 alloy consumable ingot with a diameter of 410 mm
(a) crack propagation characteristics
(b) MC and η phase interface crackings
(c) Laves phase interface cracking
Fig.11  Curves of thermal conductivity of different alloys with temperature based on JMatPro software
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