Thickness debit effect of Ni-based single crystal superalloy thin-walled specimens in the VHCF regime based on a vibration fatigue test

Abstract

This paper proposes a novel vibration fatigue testing methodology of thin-walled specimens in the very high cycle fatigue (VHCF) regime, with the lifetime up to 109 cycles. A series of novel thin-walled specimens for the single crystal superalloy DD6 are designed, considering the thickness range from 0.5 to 1.5 mm. And the influences of the wall thickness on the S–N relations are obtained at RT and 760 °C, respectively. Subsequently, the thickness debit effect of the superalloy in terms of VHCF is presented and the relevant mechanism is discussed finally. The results show the proposed fatigue testing methodology is feasible and efficient for the thin-walled specimens. It is revealed the thickness debit effect of the superalloy at 760 °C, which shows the fatigue strengths of the 0.5 mm specimens are remarkably lower than those of other thicker specimens, especially in the VHCF regime. The thickness debit effect is mainly attributed to the fatigue crack initiation assisted by oxide penetration.

Keywords

• Thickness debit effect
• Vibration fatigue
• Very high cycle fatigue
• Nickel-based single crystal superalloy