MOLECULAR-DYNAMICS MODELING OF NICKEL CRYSTALLIZATION IN THE PRESENCE OF CRYSTALLINE NUCLEI IN THE MELT
Molecular dynamics modeling of nickel crystallization in the presence of crystalline nuclei in the melt has been carried out. A model with a relatively large number of atoms was used in the work. The computational cell had the shape of a plate containing 12 specially introduced crystal nuclei - small cylindrical crystalline regions with fixed atoms. Crystalline nuclei were used because of the complexity of modeling crystallization in a molecular dynamics model from a liquid state at typical cooling rates for this method. The orientation of the crystal lattice in the nuclei was set randomly, but such that, as a result of crystallization, tilt boundaries with the misorientation axis <100> or <111> were obtained. First, the computational cell melted, and then it was kept for a long time at a constant temperature of 1500 K. The growth of crystals from nuclei did not depend on their orientation and proceeded at approximately the same rate, in connection with which the size of the resulting grains turned out to be approximately the same. The structure in them turned out to be clean and correct, which suggests that defects are formed during crystallization in the last turn - at the grain boundaries and triple junctions. Disclinations and any significant local stresses at triple junctions were not observed in this work. Free volume during crystallization was predominantly concentrated in the grain boundaries and triple junctions, and to a greater extent in the latter. In the process of crystallization in the region of triple junctions, comparatively small subgrains sometimes appeared with a different orientation from neighboring grains and were, as a rule, in a state of stretching, but they “healed” relatively quickly, being absorbed by neighboring growing grains.