International Journal of Plasticity | 2019
Cyclic damage behavior of Sanicro 25 alloy at 700 °C: Dispersed damage and concentrated damage
Abstract
Abstract The damage evolution behavior of a novel Sanicro 25 alloy was investigated based on low-cycle fatigue tests at 700\u202f°C. The results show that at relatively low total strain amplitude ( Δ e t / 2 ), the dispersed damage was dominant, which led to prolonged fatigue life. However, at relatively high Δ e t / 2 , the concentrated damage was dominant, which led to reduced fatigue life. Based on the damage characteristics, a modified Coffin-Manson equation that accounts for microporosity ( f ) was derived. The curved surface of plastic strain amplitude ( Δ e p / 2 ) - f - number of reversals to failure ( 2 N f ) shifts upward with increasing fatigue ductility exponent c . However, this curved surface shifts downward when the cyclic strength coefficient K ′ increases. A new model of micro-crack initiation considering the precipitates at the grain boundary was derived. The Gibbs free energy change of crack nucleation ( Δ G ) decreased with decreasing Δ e t / 2 . Finally, based on the prediction model of energy-based fatigue life, the theoretical formulas of the fatigue toughness W f and the fatigue cracking exponent β were derived. W f increases and β decreases with increasing Δ e p / 2 .