Effects of phase angle and dwell time on the thermo-mechanical fatigue behavior of an advanced turbine disk alloy

Abstract

In this study, the effects of phase angle and dwell time on thermal-mechanical fatigue (TMF) of a new-generation nickel-based powder metallurgy superalloy FGH4108, used for aeroengine turbine disks were studied along with detailed micro-characterization of fracture features and deformation substructures. The results indicate that the high density of dislocations and stacking faults (SFs) formed in the in-phase TMF tests cause cyclic softening during tensile half-cycle and cyclic hardening during compressive half-cycle. For the out-of-phase TMF tests, the low density of dislocations and SFs which is associated with dislocation annihilation at the highest temperature but the minimum applied mechanical strain leads to cyclic softening during tensile half-cycle and insignificant cyclic hardening during compressive half-cycle. The combined effect of high temperature and high applied mechanical strain in the in-phase TMF tests promote grain boundary deformation and oxidation, leading to mixed transgranular and intergranular crack initiation and propagation, especially when a dwell is introduced at the peak temperature and load, while cracks mainly are transgranular in the out-of-phase TMF tests. The TMF life under the investigated conditions is predominantly influenced by the crack propagation process, the much lower maximum tensile stress in the in-phase TMF tests contribute to much longer life of the in-phase non-dwell test compared with that of the out-of-phase TMF tests.