Multi-stage dwell fatigue crack growth behaviors in a nickel-based superalloy at elevated temperature

• Published in: Engineering fracture mechanics 2021-08, Vol.253, p.107859, Article 107859
• Main Authors: Wang, Ji, Wang, Run-Zi, Zhang, Xian-Cheng, Ye, You-Jun, Cui, Yan, Miura, Hideo, Tu, Shan-Tung
• Format: Article
• Language: English
• Subjects: Crack growth; Crack propagation; Dwell fatigue; Dwell time; EBSD analysis; Fatigue failure; Fatigue life; Fracture mechanics; High temperature; Morphology; Nickel; Nickel base alloys; Nickel-based superalloy; Replica technique; Superalloys; Twin boundaries
• ISSN: 0013-7944; 1873-7315
• DOI: 10.1016/j.engfracmech.2021.107859

•Replica technique is to obtain multi-stage DFCG rate and retrospect micro mechanism.•Full length dwell fatigue tests guarantee in-depth understanding in DFCG behaviors.•Comprehensive EBSD mapping analysis reveals high DFCG resistance at Σ3 TBs.•High-resolution TEM analysis is supplemented to explore two morphologies of Σ3 TBs. A series of continuous and interrupted cyclic tests in Inconel 718 with the dwell times ranging from 0 s to 10,800 s at 650 °C were carried out in order to study the multi-stage dwell fatigue crack growth (DFCG) behavior. Replica technique was used to measure the intermittent DFCG rates from short to long periods and to retrospect specific damage mechanisms based on microstructural characterizations. From the macroscopic viewpoint, the DFCG curves were classified into short, moderate and long dwell conditions according to the tendencies in DFCG rates. Correspondingly, the dwell fatigue life distribution was divided into three periods, which exhibit different sensitivities in the length of dwell time on dwell fatigue life. From the microscopic viewpoint, the high-scattered points reflected in the DFCG curves were elaborately discussed with the combinations of EBSD mapping and high-resolution TEM analysis. Σ3 twin boundaries (Σ3 TBs) were regarded as the barriers to resist the DFCG due to their special performances. In addition, with the increase of dwell times, the main crack morphologies changed from transgranular to intergranular mode. Simultaneously, local crack growth modes at high-scattered points changed from across to along the Σ3 TBs with extreme low DFCG rates. Also, high-angle crack deflection was another factor that was responsible for the decrease of the DFCG rates.