Abstract
In this study, we examine the mechanism of fatigue-crack propagation in 718Plus superalloy at 704 °C under fatigue–creep–environment interactions, in this case, a new turbine disc material used in aero-engines at high temperatures. The effect of creep on the fatigue-crack propagation of the superalloy at high temperature was also researched. There was an unusual inhibitory effect on the propagation of fatigue cracks in 718Plus alloy, in which the propagation rate of fatigue cracks decreased with the increase of creep time through exploration of dwell-fatigue-crack growth (DFCG) test with different creep times. In particular, under lower stress intensity factor range (ΔK) conditions, the fatigue-crack growth rate with a 90 s hold-time was one order of magnitude lower than that with a 5 s hold-time. Conversely, the gap between the two DFCGs gradually decreased with the increase of ΔK and the creep effect became less apparent. The mechanism of crack propagation in 718Plus alloy under two creep conditions was investigated from a viewpoint of the microstructure, oxidation rate at high temperature and crack path morphology under different conditions.
Highlights
The nickel-based superalloy 718Plus alloy combines the high temperature resistance of Waspaloy and the workability of Inconel 718 alloy
The detailed microstructure of the samples was observed by FESEM, is the grain size degree [23])
The detailed microstructure of the samples was observed by FESEM, as as shown
Summary
The nickel-based superalloy 718Plus alloy combines the high temperature resistance of Waspaloy and the workability of Inconel 718 alloy. This alloy attracts much attention from researchers due to its potentiality in the manufacture of advanced aerospace engines—especially for turbine discs, in which it must withstand complex interactions of fatigue, creep and oxidation at high temperatures under alternate loading and high temperature corrosion environments [1,2,3]. Kennedy et al [1] measured fatigue-crack growth rates of Inconel 718, Waspaloy and 718Plus alloys, where the tests were performed at 650 ◦ C and 704 ◦ C with a zero and a 100 s hold-time. Liu et al [18]
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