Please wait a minute...
Acta Metall Sin  2020, Vol. 56 Issue (12): 1654-1666    DOI: 10.11900/0412.1961.2020.00147
Current Issue | Archive | Adv Search |
Cooling Rate Driven Thin-Wall Effects on the Microstructures and Stress Rupture Properties of K465 Superalloy
GUO Xiaotong1,2, ZHENG Weiwei1, LI Longfei1, FENG Qiang1()
1 State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China
2 China Electronic Product Reliability and Environmental Testing Research Institute, Guangzhou 510610, China
Cite this article: 

GUO Xiaotong, ZHENG Weiwei, LI Longfei, FENG Qiang. Cooling Rate Driven Thin-Wall Effects on the Microstructures and Stress Rupture Properties of K465 Superalloy. Acta Metall Sin, 2020, 56(12): 1654-1666.

Download:  HTML  PDF(5874KB) 
Export:  BibTeX | EndNote (RIS)      
Abstract  

The designed service temperature of turbine blades is rising with the increasing thrust of aircraft engines. A film cooling system is one of the promising ways to improve the service temperature of turbine blades. However, such a complex film cooling system can reduce the thickness of the blade airfoil and lead to obvious local differences in microstructure; these differences are caused by solidification and mechanical resistance between the blade airfoil and alloys such as standard solid bars. In this study, a thin-walled tube manufactured by the casting process was used to simulate the microstructure of the hollow blade airfoil. The tube was thermally exposed at a temperature range of 900~1050 ℃ for 300~1000 h, and the corresponding stress rupture properties under 975 ℃ and 225 MPa (pressure) were examined. The microstructures were investigated using OM, SEM, TEM, and XRD, and the chemical compositions of the precipitates formed were measured through physicochemical phase analysis before and after the thermal exposure. Through this analysis, the relationship between microstructural degradation and stress rupture properties was revealed. The results indicated that dissolution and coarsening of γ' precipitates, degeneration of MC carbides, and broadening of the γ' film along the grain boundaries occurred in the K465 alloy tube during thermal exposure between 900 ℃ and 1050 ℃. With increasing exposure temperatures and prolonged thermal exposure time, the degree of degradation of the γ' precipitates, carbides, and grain boundaries gradually increased. This resulted in a gradual reduction in stress rupture lives. Unlike the phenomenon observed in our previous study in which a large amount of μ phase precipitated in the solid bar following thermal exposure at 900 ℃; in the present study, the μ phase did not form in the tube. However, the degrees of microstructural degradation in the tube and bar were similar after the thermal exposure at 1000 and 1050 ℃. The stress rupture lives of the tube were significantly higher than those of the bar after the thermal exposure at 900 ℃, whereas their stress rupture lives were similar after the thermal exposure at 1000 and 1050 ℃. The thin-wall effect caused by the cooling rate on the microstructure and the corresponding stress rupture property of K465 alloy was obvious at 900 ℃, whereas it was negligible at 1000 and 1050 ℃. These results provided guidance for the manufacturing and evaluation of microstructural degradation of turbine blades made of conventionally cast polycrystalline superalloys.

Key words:  K465 alloy      turbine blade      thin-wall effect      microstructure      stress rupture property     
Received:  06 May 2020     
ZTFLH:  TG146.1  
Fund: National Key Research and Development Program of China(2016YFB0701403);National Natural Science Foundation of China(51631008);National Natural Science Foundation of China(91860201)

URL: 

https://www.ams.org.cn/EN/10.11900/0412.1961.2020.00147     OR     https://www.ams.org.cn/EN/Y2020/V56/I12/1654

Fig.1  Sketch of the stress rupture spcimen of the tube of K465 alloy (unit: mm)
Fig.2  Typical as-received microstructures of the K465 alloy tube after the standard heat treatment

Exposure temperature

Exposure time

h

Af

%

W

μm

As-received-63.2±2.23.4±0.7
90030066.1±1.73.9±0.9
50066.8±0.65.8±0.7
100066.1±1.56.2±0.4
100030064.4±1.66.4±0.2
50063.0±1.87.6±1.7
100061.8±2.58.6±0.8
105030052.2±1.16.9±1.1
50048.9±1.98.3±0.1
100047.6±1.09.0±1.6
Table 1  The area fractions of γ' precipitates (Af) in the dendrite core regions and the widths of γ' film (W) along the grain boundaries in the K465 alloy tube after the standard heat treatment and after thermal exposure at 900~1050 ℃
Fig.3  SEM-SE images of γ' precipitates in the dendrite core regions of the K465 alloy tube after different thermal exposure conditions
Fig.4  SEM-BSE images showing the two-dimentional morphologies of the interdendritic regions in the K465 alloy tube after thermal exposure conditions of 900 ℃, 300 h (a), 900 ℃, 1000 h (b), 1000 ℃, 1000 h (c) and 1050 ℃, 1000 h (d), and SEM-SE images showing the three-dimentional morphologies after thermal exposure at 1050 ℃ for 300 h with low (e) and high (f) magnifications
Fig.5  TEM images of the plate-like M6C carbide (a) and the granular M23C6 carbide (b), and corresponding SAED patterns (insets) of the K465 alloy tube after thermal exposure at 1000 ℃ for 1000 h
Fig.6  SEM-BSE images showing the two-dimentional morphologies of grain boundaries in the K465 alloy tube after thermal exposure conditions of 900 ℃, 1000 h (a), 1000 ℃, 1000 h (b) and 1050 ℃, 1000 h (c), and SEM-SE image showing the corresponding three-dimentional morphology after thermal exposure at 1050 ℃for 1000 h (d)
Fig.7  XRD spectra of the extracted carbides in the K465 alloy tube
Fig.8  Mass fractions of various carbides in the K465 alloy tube after the standard heat treatment and after thermal exposure at 900 and 1000 ℃ for 1000 h, respectively
Exposure conditionCarbideWNiCrCoMoTiNbC*
As-receivedMC9.6201.1802.4525.1411.6150.00
M6C24.9215.4121.1310.839.401.802.2214.29

900 ℃,1000 h

MC8.2201.1302.3525.4412.8750.00
M6C24.2211.9522.4814.327.212.752.7914.29
M23C65.003.5266.241.742.810020.69

1000 ℃, 1000 h

MC6.9500.9602.2725.7414.0850.00
M6C25.1614.6121.1311.789.021.632.3814.29
M23C66.234.0764.172.012.830020.69
Table 2  Chemical compositions of carbides in the K465 alloy tube after the standard heat treatment and after thermal exposure at 900 and 1000 ℃ for 1000 h by using physicochemical phase analysis
Fig.9  Stress rupture lives of the K465 alloy bar[14] and K465 alloy tube at 975 ℃, 225 MPa after the standard heat treatment and after thermal exposure at 900 ℃ (a), 1000 ℃ and 1050 ℃ (b)
Fig.10  SEM-BSE images of the cracks at the longitudinal sections close to the fracture surface of stress rupture specimens in the K465 alloy tube after different thermal exposure conditions
Fig.11  Phase equilibrium diagram of K465 alloy representing the phase constitutions between 700 ℃ and 1400 ℃ based on Thermo-Calc software
PhasePrecipitation temperature / ℃

Mass fraction at

900 ℃ / %

Mass fraction at

1000 ℃ / %

Mass fraction at

1050 ℃ / %

γ'<121363.656.446.9
MC>1013000.7
M6C843~11103.04.13.3
M23C6<10332.11.50
μ<866000
Table 3  Precipitation temperature ranges and mass fractions of secondary phases in the K465 alloy tube based on Thermo-Calc software between 700 ℃ and 1400 ℃
[1] Bunker R S, Wallace T T. Turbine airfoil with double shell outer wall [P]. US Pat, 5328331A, 1994
[2] Jackson M R, Skelly D W, Rowe R G, et al. Double wall turbine parts [P]. US Pat, 5820337A, 1998
[3] Bunker R S, Huang S C, Klug F J. Cooling of a double walled turbine blade and method of fabrication [P]. EP Pat, 1369554A1, 2003
[4] Liang G. Thin turbine rotor blade with sinusoidal flow cooling channels [P]. US Pat, 7753650 B1, 2010
[5] Chung V, Ortiz M, Poon K. Thin wall cooling system [P]. US Pat, 6478535 B1, 2002
[6] Zheng Y R. Size effects of thin section for single crystal turbine blade superalloys [J]. J. Mater. Eng., 2007, (7): 74
(郑运荣. 单晶涡轮叶片合金的薄截面尺寸效应 [J]. 材料工程, 2007, (7): 74)
[7] Seetharaman V, Cetel A D. Thickness debit in creep properties of PWA 1484 [A]. Superalloys 2004: Proceedings of the 10th International Symposium on Superalloys [C]. Seven Springs, Pennsylvania: TMS, 2004: 207
[8] Duhl D N. Directionally solidified superalloys [A]. Superalloys II High Temperature Materials for Aerospace and Industrial Power [C]. New York: John Wiley and Sons, 1987: 189
[9] Zheng Y R, Cai Y L. Notable problems in microstructure analysis of superalloy castings [J]. J. Mater. Eng., 1982, (6): 29
(郑运荣, 蔡玉林. 高温合金铸件显微组织分析中值得注意的问题 [J]. 材料工程, 1982, (6): 29)
[10] Pal J, Srinivasan D, Cheng E. Effect of rejuvenation heat treatment and aging on the microstructural evolution in René N5 single crystal Ni base superalloy blades [A]. Superalloys 2016: Proceedings of the 13th International Symposium of Superalloys [C]. Seven Springs, Pennsylvania: TMS, 2016: 285
[11] Brunner M, Bensch M, Völkl R, et al. Thickness influence on creep properties for Ni-based superalloy M247LC SX [J]. Mater. Sci. Eng., 2012, A550: 254
[12] Academic Committee of the Superalloys, CSM. China Superalloys Handbook [M]. Beijing: Standards Press of China, 2012: 232
(中国金属学会高温材料分会. 中国高温合金手册 [M]. 北京: 中国标准出版社, 2012: 232)
[13] Yuan X F, Song J X, Zheng Y R, et al. Abnormal stress rupture property in K465 superalloy caused by microstructural degradation at 975 ℃/225 MPa [J]. J. Alloys Compd., 2016, 662: 583
doi: 10.1016/j.jallcom.2015.12.086
[14] Yuan X F, Song J X, Zheng Y R, et al. Quantitative microstructural evolution and corresponding stress rupture property of K465 superalloy [J]. Mater. Sci. Eng., 2016, A651: 734
[15] Yang J X, Zheng Q, Sun X F, et al. Morphological evolution of γ' phase in K465 superalloy during prolonged aging [J]. Mater. Sci. Eng., 2007, A457: 148
[16] Yang J X, Zheng Q, Sun X F, et al. Formation of μ phase during thermal exposure and its effect on the properties of K465 superalloy [J]. Scr. Mater., 2006, 55: 331
doi: 10.1016/j.scriptamat.2006.04.032
[17] Guo X T, Zheng W W, Xiao C B, et al. Evaluation of microstructural degradation in a failed gas turbine blade due to overheating [J]. Eng. Fail. Anal., 2019, 103: 308
doi: 10.1016/j.engfailanal.2019.04.021
[18] Yuan X F. The assessment of normal service induced damage in high pressure turbine blades made of equiaxed crystal cast superalloy K465 [D]. Beijing: University of Science and Technology Beijing, 2015
(袁晓飞. 等轴晶铸造K465合金高压涡轮叶片正常服役损伤及其评价研究 [D]. 北京: 北京科技大学, 2015)
[19] Guo X T, Antonov S, Lu F, et al. Solidification rate driven microstructural stability and its effect on the creep property of a polycrystalline nickel-based superalloy K465 [J]. Mater. Sci. Eng., 2020, A770: 138530
[20] Jeong H W, Seo S M, Choi B G, et al. Effect of long-term thermal exposures on microstructures and mechanical properties of directionally solidified CM247LC alloy [J]. Met. Mater. Int., 2013, 19: 917
doi: 10.1007/s12540-013-5003-5
[21] Cheng K Y, Jo C Y, Kim D H, et al. Influence of local chemical segregation on the γ′ directional coarsening behavior in single crystal superalloy CMSX-4 [J]. Mater. Charact., 2009, 60: 210
doi: 10.1016/j.matchar.2008.09.002
[22] Sun W, Qin X Z, Guo J T, et al. Thermal stability of primary MC carbide and its influence on the performance of cast Ni-base superalloys [J]. Mater. Des., 2015, 69: 81
doi: 10.1016/j.matdes.2014.12.038
[23] Qin X Z, Guo J T, Yuan C, et al. Long-term thermal exposure responses of the microstructure and properties of a cast Ni-base superalloy [J]. Mater. Sci. Eng., 2012, A543: 121
[24] Reed R C. The Superalloys: Fundamentals and Applications [M]. New York: Cambridge University Press, 2006: 90
[25] Godovanets M A, Prusakov B A, Lysenko I I. Regenerative heat treatment of blades of high-temperature nickel alloys [J]. Met. Sci. Heat Treat., 1996, 38: 202
doi: 10.1007/BF01397020
[26] Johnston J R, Dreshfield R L, Collins H E. Effect of casting geometry on mechanical properties of two nickel-base superalloys [R]. Ohio: NACA Technical Memorandum X-3386, 1976
[27] Lloyd R D. The effect of casting variables and section size on the stress-rupture life of a high temperature nickel base alloy [A]. AIME Spring Meeting [C]. Pittsburgh: SAE International, 1969: 1
[28] Bensch M, Fleischmann E, Konrad C H, et al. Secondary creep of thin-walled specimens affected by oxidation [A]. Superalloys 2012: Proceedings of the 12th International Symposium on Superalloys [C]. Seven Springs, Pennsylvania: TMS, 2012: 387
[29] Yang J X, Zheng Q, Sun X F, et al. Morphological evolution of MC carbide in K465 superalloy [J]. J. Mater. Sci., 2006, 41: 6476
doi: 10.1007/s10853-006-0684-5
[30] Yang J X, Zheng Q, Sun X F, et al. Morphological evolution of γ′ phase in K465 superalloy during thermal fatigue [J]. Trans. Nonferrous Met. Soc. China, 2006, 16: 1986
[31] Wang F, Ma D X, Bührig-Polaczek A. Eutectic formation during solidification of Ni-based single-crystal superalloys with additional carbon [J]. Metall. Mater. Trans., 2017, 48A: 5442
[32] Gong L, Chen B, Zhang L, et al. Effect of cooling rate on microstructure, microsegregation and mechanical properties of cast Ni-based superalloy K417G [J]. J. Mater. Sci. Technol., 2018, 34: 811
doi: 10.1016/j.jmst.2017.03.023
[1] ZHANG Leilei, CHEN Jingyang, TANG Xin, XIAO Chengbo, ZHANG Mingjun, YANG Qing. Evolution of Microstructures and Mechanical Properties of K439B Superalloy During Long-Term Aging at 800oC[J]. 金属学报, 2023, 59(9): 1253-1264.
[2] LU Nannan, GUO Yimo, YANG Shulin, LIANG Jingjing, ZHOU Yizhou, SUN Xiaofeng, LI Jinguo. Formation Mechanisms of Hot Cracks in Laser Additive Repairing Single Crystal Superalloys[J]. 金属学报, 2023, 59(9): 1243-1252.
[3] GONG Shengkai, LIU Yuan, GENG Lilun, RU Yi, ZHAO Wenyue, PEI Yanling, LI Shusuo. Advances in the Regulation and Interfacial Behavior of Coatings/Superalloys[J]. 金属学报, 2023, 59(9): 1097-1108.
[4] WANG Lei, LIU Mengya, LIU Yang, SONG Xiu, MENG Fanqiang. Research Progress on Surface Impact Strengthening Mechanisms and Application of Nickel-Based Superalloys[J]. 金属学报, 2023, 59(9): 1173-1189.
[5] CHEN Liqing, LI Xing, ZHAO Yang, WANG Shuai, FENG Yang. Overview of Research and Development of High-Manganese Damping Steel with Integrated Structure and Function[J]. 金属学报, 2023, 59(8): 1015-1026.
[6] LI Jingren, XIE Dongsheng, ZHANG Dongdong, XIE Hongbo, PAN Hucheng, REN Yuping, QIN Gaowu. Microstructure Evolution Mechanism of New Low-Alloyed High-Strength Mg-0.2Ce-0.2Ca Alloy During Extrusion[J]. 金属学报, 2023, 59(8): 1087-1096.
[7] LIU Xingjun, WEI Zhenbang, LU Yong, HAN Jiajia, SHI Rongpei, WANG Cuiping. Progress on the Diffusion Kinetics of Novel Co-based and Nb-Si-based Superalloys[J]. 金属学报, 2023, 59(8): 969-985.
[8] SUN Rongrong, YAO Meiyi, WANG Haoyu, ZHANG Wenhuai, HU Lijuan, QIU Yunlong, LIN Xiaodong, XIE Yaoping, YANG Jian, DONG Jianxin, CHENG Guoguang. High-Temperature Steam Oxidation Behavior of Fe22Cr5Al3Mo-xY Alloy Under Simulated LOCA Condition[J]. 金属学报, 2023, 59(7): 915-925.
[9] ZHANG Deyin, HAO Xu, JIA Baorui, WU Haoyang, QIN Mingli, QU Xuanhui. Effects of Y2O3 Content on Properties of Fe-Y2O3 Nanocomposite Powders Synthesized by a Combustion-Based Route[J]. 金属学报, 2023, 59(6): 757-766.
[10] FENG Aihan, CHEN Qiang, WANG Jian, WANG Hao, QU Shoujiang, CHEN Daolun. Thermal Stability of Microstructures in Low-Density Ti2AlNb-Based Alloy Hot Rolled Plate[J]. 金属学报, 2023, 59(6): 777-786.
[11] GUO Fu, DU Yihui, JI Xiaoliang, WANG Yishu. Recent Progress on Thermo-Mechanical Reliability of Sn-Based Alloys and Composite Solder for Microelectronic Interconnection[J]. 金属学报, 2023, 59(6): 744-756.
[12] WANG Fa, JIANG He, DONG Jianxin. Evolution Behavior of Complex Precipitation Phases in Highly Alloyed GH4151 Superalloy[J]. 金属学报, 2023, 59(6): 787-796.
[13] WU Dongjiang, LIU Dehua, ZHANG Ziao, ZHANG Yilun, NIU Fangyong, MA Guangyi. Microstructure and Mechanical Properties of 2024 Aluminum Alloy Prepared by Wire Arc Additive Manufacturing[J]. 金属学报, 2023, 59(6): 767-776.
[14] ZHANG Dongyang, ZHANG Jun, LI Shujun, REN Dechun, MA Yingjie, YANG Rui. Effect of Heat Treatment on Mechanical Properties of Porous Ti55531 Alloy Prepared by Selective Laser Melting[J]. 金属学报, 2023, 59(5): 647-656.
[15] LIU Manping, XUE Zhoulei, PENG Zhen, CHEN Yulin, DING Lipeng, JIA Zhihong. Effect of Post-Aging on Microstructure and Mechanical Properties of an Ultrafine-Grained 6061 Aluminum Alloy[J]. 金属学报, 2023, 59(5): 657-667.
No Suggested Reading articles found!