High Temperature Very-High-Cycle Fatigue Behaviour and Lifetime Prediction of Ni-base Superalloys

Chen Bo ^1*, Zhao Zihua ²

¹ School of Engineering, University of Leicester, LE1 7RH

² School of Materials Science and Engineering, Beihang University, Beijing 100191, China

EXTENDED ABSTRACT:Fatigue is the single largest failure reason based on the jet engine component distress mode statistics. According to the Engine Structural Integrity Program, initiated by the USA Department of Defense, all engine parts should have a minimum fatigue life of 109 cycles. Very-high-cycle fatigue (VHCF) at high temperature has been studied on Ni-base superalloys in the form of single-crystal, columnargrained and polycrystal. This paper aims to elucidate the oxidation-fatigue interaction and the effect of surface recrystallisation on the VHCF behaviour and lifetime prediction for both the single-crystal and columnargrained superalloys (DD6 and DZ125 alloys). A range of VHCF tests were conducted over a wide range of temperatures from 760 to 1100 C, which was followed by performing post-mortem examinations [1-3]. Detailed considerations of the fractography and microstructural features provided quantitative descriptions of important factors that control the fatal-crack initiation and propagation. An attempt was thus made to establish a fatigueindicator-parameter based VHCF life prediction model for Ni-base superalloys. Opportunities and challenges are explained about this research field with the aim to stimulate future work, given that comparably less research efforts have been made in China than USA and the Europe.
REFERENCES

[1] Z. Zhao, Q. Li, F. Zhang, W. Xu, B. Chen, Transition from internal to surface crack initiation of a singlecrystal superalloy in the very-high-cycle fatigue regime at 1100 °C, Int. J. Fatigue. 150 (2021) 106343: 1–14.
[2] Z. Zhao, F. Zhang, C. Dong, X. Yang, B. Chen, Initiation and early-stage growth of internal fatigue cracking under very-high-cycle fatigue regime at high temperature, Metall. Mater. Trans. A. 51 (2020) 1575–1592.
[3] Z. Zhao, Z. Liang, Q. Li, F. Zhang, B. Chen, Crack initiation and propagation behaviour under hightemperature very-high-cycle fatigue: directionally solidified columnar-grained vs. single-crystal superalloys (Submitted and Under Revision)