How Can the Non-metallic Inclusion Distributions Lead to an Anisotropy in the Fatigue Life Durability of Forged γ/γ′ Ni-Based Disks Alloys?

The impact of non-metallic inclusionsNon-metallic inclusions (NMIs) and the forgingForging process on the low-cycle fatigueFatigue (LCF) durability of a γ/γ′ superalloySuperalloys is investigated. X-ray synchrotron tomography was performed to characterize the NMI populations. Low cycle fatigueLow cycle fatigue was tested at 400 °C on specimens taken in various orientations on forged disksDisk using the ring rollingRing rolling process or the die forgingForging one. The results show anisotropic tensile and fatigueFatigue properties for the ring rolled disksDisk, especially in radial and axial directions. On the other hand, no reduction of the lifespan was observed for the die-forged ones. Fractographic observations and a macroscopic approach in modellingModelling of a particle during forgingForging were conducted. It showed that abnormal low lifetimes are connected to crack initiationCrack initiation at NMIs. However, it is not a sufficient condition. The length of NMI stringers and their orientation in the diskDisk are important parameters. The forgingForging process has a strong impact on the plastic flow and the initial state of the particles. Indeed, ring rollingRing rolling promotes decohesion at the interface between the inclusion and the matrix. The crack initiationCrack initiation time and the first stages of the propagation to the matrix highly contribute to low lifespan. A better understanding of the detrimental configurations of NMIsNon-metallic inclusions would allow optimized forgingForging processes.