Atomic mechanisms of structural reconstruction having place in the block of nanocrystal at an impulsive tension deformation were studied by the method of molecular dynamics. The block of nanocrystal was presented by a rectangular parallelepiped with the sides corresponding to the planes  of FCC lattice. The number of atoms of the calculated block ranged from 2*10^4 to 10^5.Free boundary conditions were applied along tension direction. The velocity of the change of deforming loading amounted to 20 m/s. The model blocks of crystals of pure metals Ni, Al and Ni3Al intermetallide with the atomic pacing corresponding to the structure L12. It was supposed that there were no defects in the calculated block. Four main stages are distinct seen on the graphs of the change of the stored energy of deformation on the value of the applied deforming stress. They are the following: 1) quasielastic deformation, 2) plastic deformation, 3) flow, 4) fracture. The first stage is characterized by the growth of energy according the parabolic low. The formation and storing of dynamic pairs of point defects vacancies and interstitial atoms is observed at this stage. The formation of dislocation loops and the displacements of crystal parts along the planes  took place at definite concentrations of such defects. Sharp jump-like decrease of energy is seen on the graph of the dependence of the stored energy on time (value of deforming loading). The stage of plastic deformation is characterized by a new growth of stored energy but the growth process takes place more slowly. In this connection, the storing of dislocations and the appearance of the neck is observed. At the flow stage, the stored energy is not practically changed up to the fracture. The comparison of the curves of deformation development was made for the alloys under study and Ni3Al.