Effect of dwell time and stress intensity factor on crack deflection at elevated temperature of nickel-based superalloy GH4169 with forming induced δ-phase clusters

To achieve more accurate crack propagation analysis of GH4169 with forming induced δ-phase clusters, which often experiences load-related crack deflection, a crack deflection criterion is necessary. This paper develops such a criterion based on experimental studies of critical load conditions and mechanisms that induce crack deflection. Crack propagation tests were performed at 650 °C using a novel loading waveform. Various dwell loads with different dwell times (t_d) were introduced at the peak of triangular cyclic loads under different initial stress intensity factors (K_initial) to study the effect of dwell load on crack deflection. Observations of the macroscopic crack path showed that increased t_d or K_initial induced crack deflection. Fracture surface analysis and in-situ observation tests revealed that δ-phase clusters with a preferred orientation cause creep cracks to propagate along the orientation during applying dwell load, leading to overall crack deflection. Based on these comprehensive understandings, a crack deflection criterion was developed. This criterion integrates a single fitting parameter with a well-known creep crack propagation model, expressed as K_initial^2.17 · t_d ≥ 945,528 for GH4169. Here, 2.17 is the exponent for the stress intensity factor in the creep crack propagation model, and 945,528 is the only fitting parameter.