Saturation effect of creep-fatigue cyclic-life for Nickel-based superalloy DZ445 under long-term tensile dwell periods at 900 °C

Abstract

This investigation determined the creep-fatigue cyclic-life (Nf) saturation effect for the DZ445 superalloy with 16–128 min dwell time at 900 °C and total strain range of 1.6%. When the dwell time exceeds 8 min, the mechanical response including maximum stress response, hysteresis loop, plastic strain range, and stress relaxation amount at characteristic cycle are also saturated with dwell time gradually. The Nf saturation effect is also reflected in the creep- and ductile-dominated fracture modes. This critical phenomenon is closely related to the dynamic equilibrium reached between the superdislocations of a/2[101] in γˊ precipitation and the formation of the dislocation networks. While the rupture time is increased continuously with dwell time, which could be better used as an evaluation index when the cyclic life is saturated. The Nf saturation effect can not only reduce the cost of tests with long-dwell time, but also provide the guidance for creep-fatigue safety design.

Keywords

• Creep-fatigue
• Saturation of cyclic life
• Long-term dwell time
• Mechanical response
• Damage mechanism