Superior fatigue crack growth resistance, irreversibility, and fatigue crack growth–microstructure relationship of nanocrystalline alloys

Failure of metals III: Fracture and fatigue of nanostructured metallic materials

“…These dislocations interact with a twin present in the near crack tip region and the motion of these dislocations is impeded during forward loading resulting in residual dislocations incorporated within the TB producing either a thickening of the twin or a de-twinning effect (Fig 14d4 and d5). A recent review about these dislocation-twin reactions can be found in Sangid et al [261] and in Pineau [113]. Fig 14d6 illustrates the situation which can take place during the reverse loading where dislocations are also emitted but contrarily to Fig 14d3 the crack tip does not advance during the half cycle.…”

“…The role of mechanical twins on crack propagation has been investigated by several authors, in particular by Sangid et al [250][251][252]261] in their study on the FCG behavior of NC Ni-Co alloys, and Kamaya [244], Blochwitz [245], Dunne [246], Christian [99], Gray [247], Man et al [249]. The mechanisms proposed by Sangid et al [261] to explain the beneficial role of mechanical twins on the FCG are schematically depicted in Fig 14d. This figure shows the emission of dislocations from the crack tip during the loading of the material.…”

“…The mechanisms proposed by Sangid et al [261] to explain the beneficial role of mechanical twins on the FCG are schematically depicted in Fig 14d. This figure shows the emission of dislocations from the crack tip during the loading of the material. These dislocations interact with a twin present in the near crack tip region and the motion of these dislocations is impeded during forward loading resulting in residual dislocations incorporated within the TB producing either a thickening of the twin or a de-twinning effect (Fig 14d4 and d5).…”

“…However, there are a few exceptions to this rule. NC Ni-Co alloys show superior resistance to fatigue crack growth [261]. The addition of Co to Ni increases the strength of the material by refining the grain size and by reducing the SFE, thereby increasing the prevalence of mechanical twinning.…”

Brief review on high-cycle fatigue with focus on non-metallic inclusions and forming

“…[23]), but it is worth to note that Sangid et al have recently successfully used a physically-based crack initiation criterion and micromechanics to predict non-inclusion-induced fatigue scatter for U720 [27,28,29]. Their model stems from the material sciences side and dislocation dynamics.…”