In situ tem investigation of crack propagation in single crystal Ni₃Al

The initiation and propagation of cracks in (110)[110] oriented Ni₃Al alloy single crystals have been investigated by in situ tension in TEM at room temperature. The results show that crack propagation appears to be in a zigzag manner and the main crack propagation orientation is along the direction of the tensile axis. The trace analysis shows the two major slip planes, (111) and (111) are activated firstly, and then the other two primary slip planes, (111) and (111) are activated. A model was proposed to explain the observed results. The calculated result of the stress fields shows that the choice of the secondary slip system is dictated by stress concentration which arises from the dislocation pile-up and makes the main crack propagation orientation parallel to the tensile axis.