NUCLEATION PROCESS OF MARTENSITE IN SMALL PARTICLES

The atomic mechanism of the nucleation process of the martensite from the metastable austenite is studied by use of the computer simulation, It is investigated whether the finite displacement of one atom, which is known to take place in any lattice as a part of the vacancy migration, can trigger the nucleation process of the martensite in two types of model crystals. One is more stable with respect to (110) shear than the other. The nucleation process is triggered in both types of crystals by the displacement of one atom, if the periodic boundary condition which is assumed to simulate an infinitely large crystal is adopted. However, in a small crystal with 1241 atoms, the nucleation process is not triggered by the displacement of one atom in the more stable model crystal. This indicates the presence of a mechanism that stabilizes the crystal against the nucleation of the martensite in a small crystal. In a less stable model crystal, the nucleation process in a small particle is triggered in the same way as in an infinite crystal.