Atomistic simulations of Paidar–Pope–Vitek lock formation in Ni3Al

The thermally activated process of Paidar–Pope–Vitek (PPV) lock formation in the L12 intermetallic Ni3Al is simulated using the “nudged elastic band” method with an embedded atom potential. It is found that the one-step PPV lock is intrinsically unstable, but it can be stabilized by a large enough Escaig stress. The two-step PPV lock can be formed with a low activation energy when the one-step lock is involved as an intermediate step. In this case, the overall activation energy is about 1 eV, in reasonable agreement with the range of 0.5–0.9 eV expected from experimental observation of the flow stress anomaly in Ni3Al. High Escaig stresses are required to stabilize the one-step lock, and the absence of such high stresses in the micro-strain regime is thought to be the underlying reason for the absence of the flow stress anomaly in micro-strain conditions.