[SY-E7] The Activation Parameters for Dislocation Nucleation in Molybdenum Nanoparticles under Compression
Invited
Metallic faceted nanoparticles exhibit ultra-high strength, since their deformation involves the nucleation of dislocations on their surfaces. In this work, we employ molecular dynamics (MD) simulations to study the strength of molybdenum faceted nanoparticles and its relation to the activation parameters for dislocation nucleation [1]. We show that under compression, the nanoparticles yield by nucleating dislocations at the vertices, which are points of stress concentration. For each temperature, the simulation is repeated 30 times with different atomic velocities. Since dislocation nucleation is a thermally-activated process, the calculated strength varies between the different simulations. The strength distribution can be exploited to calculate the activation parameters. We show that the distribution can be approximated by a normal distribution, with a standard-deviation that corresponds directly to the activation volume at the given temperature and stress. Accordingly, the activation volumes are calculated from the MD simulation results at different temperatures and stresses. In addition, the dependence of the most-probable nucleation stress on the temperature is calculated. With the help of classical nucleation theory, the activation free-energy and the activation entropy are calculated. We find that the dependence of the activation free-energy on the stress obeys a power-law near the conditions for spontaneous nucleation, with a critical exponent that is equal ~1.5. This critical exponent is typical for simple bifurcation problems. In addition, the activation entropies are found to be in the range of 0-15kB, with some deviations form the Meyer-Neldel compensation rule. Based on the calculated activation parameters, the probabilistic nature of the strength at this scale is discussed.
1. Chachamovitz D, Mordehai D. Sci Rep 2018;8:3915
1. Chachamovitz D, Mordehai D. Sci Rep 2018;8:3915