Fatigue crack propagation behavior of the grain size transition zone in a dual microstructure turbine disc

Constant load amplitude , Delta K fatigue crack propagation (FCP) tests have been carried out to investigate FCP behavior of grain size transition zone in a dual microstructure turbine disc. The results show grain size exerts more significant influence in the time-dependent FCP regime, but the effect of grain size is relatively limited in the cycle-dependent FCP regime. Larger local plastic deformation zone is found in fine-grained region, which is believed to be the reason that causes more significant grain boundary oxidation along with contribution from more grain boundaries acting as short-circuit diffusion paths of oxide-forming elements, resulting in accelerated FCP.