Effect of rafted microstructure and its temperature dependency on fatigue crack propagation in a single‐crystal Ni‐base superalloy

Abstract

Effects of rafted microstructure and its temperature dependency on fatigue crack propagation (FCP) in a single-crystal Ni-base superalloy are experimentally investigated. FCP tests are conducted at room temperature, 450 C, and 700 C for two types of pre-rafted specimens, and their FCP behaviors are compared with that of a specimen with cuboidal γ 0 precipitates. It is found in the experiments that there is no significant influence of rafted microstructures on FCP rate at room temperature, while a clear influence is pronounced at 450 and 700 C depending on the coarsening direction of rafted microstructures and the level of stress intensity factor range. The temperature dependency in the effect of rafted microstructure is discussed with special considerations on the microscopic FCP behavior affected by the morphology of γ 0 precipitates, the coherency of the γ/γ 0 interface, and temperature-dependent slip characteristics of γ and γ 0 phases.

Microstructure degradation and residual low cycle fatigue life of a serviced turbine blade

“…In terms of the 2.0 TBO blade sample, the crack initiated in a transgranular mode near the GB, and propagated in an open mode showing transgranular feature, as shown in Figure 15C. Besides, the crack also propagated in transgranular mode in long crack stage, possibly due to the weaken fatigue crack growth resistance caused by coarsened γ′ precipitate 48 . Notably, the fatigue resistance of the polycrystalline Ni‐based superalloy can also relate to the degenerated GB and evolution of carbides 47 .…”

“…Besides, the crack also propagated in transgranular mode in long crack stage, possibly due to the weaken fatigue crack growth resistance caused by coarsened γ 0 precipitate. 48 Notably, the fatigue resistance of the polycrystalline Ni-based superalloy can also relate to the degenerated GB and evolution of carbides. 47 However, the coarsening γ 0 precipitate of the long-term serviced blade plays a crucial role in the deterioration of fatigue life and the reduction of resistance to fatigue crack propagation.…”

Research on the Effect Mechanism of Re on Interface Dislocation Networks of Ni–Based Single Crystal Alloys

“…The sections of the γ phase and γ ′ phase are shown in Figure 8a,b, respectively, and the blue atoms in Figure 8b are Al atoms. Due to the deviation in lattice constants between the γ phase and the γ ′ phase, there are mismatched dislocations in the interface of the model, and the dislocation density is an important factor affecting the performance of Ni-based single crystal alloys [10][11][12][13][14][15]. The corresponding γ/γ ′ phase interfaces of the six models are shown in Figure 9, and the yellow atoms are Re atoms.…”