Dislocation dynamics in aluminum containing θ’ phase: Atomistic simulation and continuum modeling

We investigate the interaction of edge dislocation with θ′ phase in aluminum matrix using atomistic simulations. The thickness of θ′ phase is chosen to be constant of 2.2 nm and the diameter is varied in range from 3 to 10 nm. It is shown that first interactions of dislocation with θ′ phase occur according to the mechanism of Orowan loop formation around the obstacle. In this case, the cross-slip processes, the formation of dislocation jogs in adjacent slip plane and the emission of vacancies upon the return of a segment to the initial slip plane are possible. During these interactions, the material of θ′ phase is subjected to high shear stresses up to 3 GPa in a layer of 2 nm thickness. Such a high stress leads to a θ′ phase cutting on the third or fourth overcoming of the obstacle by dislocation. A study is carried out of the dependence of the average stress in the system on the size of inclusion and the distance between inclusions. It is shown that an increase in the diameter of inclusion causes an increase in the average stresses in the system in proportion close to the square root of the diameter of the inclusion. Increasing the distance between inclusions causes the inversely proportional reduction of the average stress. The conducted investigation of the strain rate sensitivity showed that in the case of high shear rates, the average stresses in the system continuously increase that does not allow applying the time averaging procedure to them. The described effect is also registered in the case of pure aluminum. The existence of two regions on the temperature dependence of the average stresses in the system on the strain rate in the case of θ′ phase, previously described by Yanilkin et al. (2014) for the Guinier-Prestone zones, is confirmed. In the case of high strain rates, heating of the system leads to a decrease in the dislocation velocity, while at low strain rates the dislocation velocity increases with increasing temperature at a fixed shear rate. An interesting result obtained with long-term molecular-dynamics simulations when the tracing time is up to 2 ns, there is a tendency to reduce the average stress in the system through time. This result can be explained by destruction of the structure and form of θ’ phase. The law of motion of a dislocation in the approximation of the constancy of θ′ phase properties is proposed to describe the response of the system to shear deformation. The model contains a dislocation mass, phonon friction, and takes into account the effect of the inclusion of θ’ phase through an increase in the elastic energy of a dislocation during the formation of the Orowan loop around an obstacle.