The initiation and propagation of a crack has been investigated in a (1 6 10) [110] oriented Ni 3 Al alloy single crystal by in situ TEM and using tension deformation at room temperature. The result has shown that the macropropagating direction of the crack was parallel to the tensile axis and the crack followed a zigzag path. Trace analysis indicated that the slip on (11 6 1) and ( 111) were activated during the crack propagating process. Calculations show that for this orientation of Ni 3 Al crystal, the stress concentration arising from the dislocation pile-up decided the choice of secondary slip systems and the macrodirection of the crack.MST/4843

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