ИСТИНА

The plastic deformation under high-speed deformation is studied by molecular dynamic simulation. The rate and mechanism of the nucleation and propagation of partial dislocation loop under high shear stress in aluminum-copper alloys near Guinier-Preston (GP) zones of various diameters are investigated. Dislocation nucleation rates near plain GP Cu-zones have been calculated using mean lifetime method within the range of temperatures between 100 and 700 K. Depending on temperature and applied stress the dislocation can nucleate either from the edge, or from the plain area of a GP zone. The dislocation nucleation is preceded by a generation of defect clusters formed due to local opposite atomic shifts in two adjacent (111) planes by half-length of a Burgers vector of a partial dislocation. The expansion of a partial dislocation loop can be accompanied by the formation of twins via a shift of the atoms in the internal region of the loop or the formation of the full dislocation loop. The speeds of the edge and screw segments of partial dislocation loop as a function of a shear stress component along the Burgers vector have been estimated. The model of shear stress relaxation in aluminum-copper alloys is constructed using the data from molecular dynamics simulation. It has been found that the process of the formation of new dislocation loops is responsible for the power-law dependence of the shear stress at the top of elastic precursor wave and the initial plastic strain rate observed in shock-wave experiments.