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In this paper the authors summarize the results of studies achieved
in recent years on the microscopic mechanisms of fracture of TiAl alloys: (1)
Cracks prefer to be initiated and propagated along lamellar interfaces, the
propagation of crack can take three ways. (2) Mechanism of fracture includes two
modes of critical crack triggering fracture and connection of microcracks in the
weakest section. (3) Effects of microcrack damage represent the facial effects and
the volumetric effects. (4) mechanisms of toughening include: blunting of crack
tip, bifurcation of the crack tip, deflection of the crack by lamellae and formation
of a diffuse zone of microcracks, stopping the crack at the boundary of a grain
with unfavorable orientation or grains and forcing the crack to bypass the barrier
grain and take a tortuous path, or cross the barrier grain spending more energy.