Coarsening Behaviors of Γ′ Phase in FGH99 Superalloy During LCF

During low cycle fatigue (LCF) at 400 degrees C, the coarsening behaviors of secondary/tertiary gamma ' phase in FGH99 superalloys are elucidated. As the total strain amplitude h epsilon t/2 increases, the secondary/tertiary gamma ' phases coarsen simultaneously. The coarsening behaviors of the secondary gamma ' phase rely on the formation of a dendritic structure via preferential growth within the primary gamma ' phase (h epsilon t/2 from 0.6% to 0.7%) and coalescence with adjacent secondary gamma ' phase (h epsilon t/2 = 0.8%). Additionally, the Hf-containing mu phase particle can inhibit the coarsening of the secondary gamma ' phase by restricting the formation of dendritic structures in the primary gamma ' phase. The coarsening behaviors of the tertiary gamma ' phase are related to the coalescence of cellular structures and the dissolution/ detachment of growing secondary gamma ' phase. The correlation models between the average equivalent radius and fatigue fractured time, h epsilon t/2 and fatigue life were established, respectively. The average equivalent radius exhibit a nonlinear relationship with the cyclic loading time. The prediction accuracy of LCF life is within a 1.3fold error band.