Sic And Ni <sub> 3 </ Sub> Al Along The Crystallographic Orientation Of The Extended Molecular Dynamics Study

This thesis introduces the basis concepts and theory in molecular dynamics simulations. The boundary conditons is studied in the impact of simulation results,the selection of potential function among atoms ,the determination of potential function and algorithm equation. On this basis, the stretching silicon carbide, Ni₃Al molecular dynamics model is built. In the solution process,it is far less than the actual situation to reduce the "finite size effects" by the number of simulation atoms. The edge model imposed "rigid boundary conditions."In the first part of the thesis, using molecular dynamics method with Tersoff potential, they have studied the propagation of the cracks in SiC under different temperatures, with the initial crack front directions along [100], [110], and [111] respectively. Their results showed that, it propagated by the mode of cleavage fracture, at low tension. For the crack with [100] or [111] being the crack front, at low tension, a disordered band formed at the crack tip, while under the tension that could guarantee the crack to open, a sharpness—bluntness—sharpness propagation process at the crack tip. It is easy for the crack with [110] direction to propagate, and during the propagation "orientation effect" gradually appeared with about 60 degrees departure from the initial direction. The surface of crack was almost leveling.In the second part of the thesis, using molecular dynamics method with NiAl potential, they have simulated the crystal fracture properties of Ni₃Al. First, the crack tip dislocation nucleation fired and a disordered band formed . Department disorder brought the cumulative stress to crack tip so divergent , crack propagation virtually ceased. Second, cracks appeared system transformation, and with the loading, transformation crack gradually extended to the entire system. In the transformation process, crystal symmetry formed in the front of disordered band. It weaken the relaxation, which is brought by the stress in the front of crack tip, and made the crack tip stress slowly increased until beyond the atom bond, finally crack began to expand.