Dislocation formation and twinning from the crack tip in Ni3Al: molecular dynamics simulations

The mechanism of low-temperature deformation in a fracture process of L1₂ Ni₃Al is studied by molecular dynamic simulations. Owing to the unstable stacking energy, the 0\bar {1}1] superdislocation is dissociated into partial dislocations separated by a stacking fault. The simulation results show that when the crack speed is larger than a critical speed, the Shockley partial dislocations will break forth from both the crack tip and the vicinity of the crack tip; subsequently the super intrinsic stacking faults are formed in adjacent {111} planes, meanwhile the super extrinsic stacking faults and twinning also occur. Our simulation results suggest that at low temperatures the ductile fracture in L1₂ Ni₃Al is accompanied by twinning, which is produced by super-intrinsic stacking faults formed in adjacent {111} planes.