Theses and Dissertations Collection

This study focuses on the fatigue crack growth, creep fatigue crack growth, and creep crack growth behavior of wrought and additive manufactured IN718 at 600oC. Task Group on Elevated Temperature Crack Growth (E08.06.05) initiated a round robin, ASTM Interlaboratory Study Program (ILS) assigned program number 1679, in validation of ASTM Standard E2760 using wrought IN718 compact tension specimens which were tested under fatigue crack growth and creep fatigue crack growth conditions with hold times of 0, 60 and 600 seconds. The study showed that for a hold time of 60s to an infinite hold time crack growth rate was independent of number of applied cycles and dependent on time. Additive manufactured (AM) compact tension specimens were also tested under similar conditions. The AM specimens were machined in three different orientations with respect to build direction and the results showed anisotropic behavior. Wrought and AM IN718 crack growth rates were compared and showed that for lower values of stress intensity the AM IN718 had lower crack growth rates but at higher values of stress intensity the AM IN718 material exhibited higher crack growth rates than the wrought IN718. Fracture surface analysis of wrought IN718 shows a transition from transgranular to intergranular fracture mode from the pre-crack to the creep fatigue crack growth region. The fracture surface of the various AM IN718 orientations did not resemble the fracture surface of the wrought IN718.