Tracing the creep lifetime degradation of IN738LC superalloy based on the primary carbide decomposition reaction and composition changes in the carbide regions

Document Type : Research Paper

Authors

• farsad forghani ¹
• mohsen mehdizadeh ²
• masoume rayatpour ³

¹ Niroo reseah Institute, metallurgy department

² Niroo Research institute, Metallurgy department

³ Niroo reseah Institute, Metallurgy department

Abstract

IN738LC nickel-based superalloy is widely used in different high-stress and high-temperature applications. During the service exposure, the microstructure of this alloy undergoes various damage mechanisms such as coarsening of γ′ precipitates, formation of continuous carbide network at grain boundaries, decomposition of MC carbides, and precipitation of detrimental phases. Decomposition of primary MC carbides usually occurs during the long-term high-temperature exposure and results in the reduction of mechanical properties. In the current study, the reaction of MC carbides decomposition is investigated in the microstructure of different gas turbine blades with different heat treatment and operational history. The changes in the composition of carbide regions are analyzed for different blades and compared with their remained creep lives. Since the decomposition of MC carbides to M23C6/M6C carbides is a mostly irreversible reaction, it is less affected by heat treatment and rejuvenation processes, and thereby it provides more valuable information for lifetime assessment and damage analysis of the exposed IN738LC samples. Moreover, the results of current work suggest that analyzing the multi-phase regions around primary MC carbides can be considered as an efficient method to evaluate the microstructural and mechanical degradation of in-service components.

Keywords

• IN738LC superalloy
• Long-term service
• Microstructural characteristics
• Carbide decomposition reaction

20.1001.1.22285946.1399.11.42.6.2

---

References

[1] R. Viswanathan, “Damage mechanisms and life assessment of high temperature Components“, ASM International, 1989.

[2] A. K. Koul and R. Castillo, “Creep Behavior of Industrial Turbine Balde Materials”, Proceeding of ASM 1993 Materials Congress, October 17-21, 1993, PP. 75-88.

[3] W. Hoffelner, “High Cycle fatigue life of Cast Nickel-base Superalloys IN738LC, IN 939”, Met. Trans.,Vol 13A, 1982, pp 1245-1255.

[4] E.S. Russell, “Practical life Prediction methods for thermal-mechanical fatigue of gas turbine buckets”, EPRI Workshop on high temperature  gas turbine materials, Aug. 1985.

[5] R. Viswanathan, A.C. Dolbec, “Life assessment Technology for combustion turbine blades”,

 

 

 

 

International Gas Turbine Conference, Germany, June 1986.

[6] D. J. Stephenson, J. R. Nicholls and P. Hancock, “The Erosion of Gas Turbine Blade Materials by Solid Sea Salt”, Corrosion Science, Vol. 25, No. 12 , PP. 1181-1192, 1985.

[7] J. Stringer , D.P.Whtthe , “ High Temperature Corrosion and Coating Superalloy “ , 1974 , pp 283 – 314.

[8] “Alloy IN-738: Technical data”, The International Nickel Company (INCO), NewYork.

[9] J. H. Feiger, V. P. Swaminathan, “Gas Turbine Blade Superalloy Material Property Handbook: Technical Report”,  Southwest Research Institute, Electric Power Research Institute (EPRI) 2001.

[10] آمار تفصیلی صنعت برق ایران ویژه تولید در سال 1394، شرکت مادر تخصصی توانیر، خردادماه 1395.

[11] گزارش "تدوین دانش فنی برآورد عمر باقیمانده پره های متحرک توربین گاز"، مرکز شیمی و مواد، پژوهشگاه نیرو، 1384.

[12] Simona ZLÁ, Jana DOBROVSKÁ, Bedřich SMETANA, Monika ŽALUDOVÁ, Vlastimil VODÁREK, Kateřina KONEČNÁ, Differential Thermal Analysis and Phase Analysis of Nickel Based Superalloy IN 738LC, 2010, Roznov pod Radhostem, Czech Republic, EU

[13] X. B. Hu, X. Z. Qin, J. S. Hou, L. Z. Zhou and X. L. Ma, Microstructural characterization of the M₂₃C₆ carbide in a long-term aged Ni-based superalloy, Philosophical Magazine Letters (2017), DOI: 10.1080/09500839.2016.1273554.

[14] L.Z. He, Q. Zheng, X.F. Sun, G.C. Hou, H.R. Guan, Z.Q. Hu, M23C6 precipitation behavior in a Ni-base superalloy M963, J. Mater. Sci. 40 (2005) 2959.

[15] X.Z. Qin, J.T. Guo, C. Yuan, C.L. Chen, J.S. Hou, H.Q. Ye, Decomposition of primary MC carbide and its effects on the fracture behaviors of a cast Ni-base superalloy, Materials Scie ce and Engineering A 485 (2008) 74–79.