COMPUTER-SIMULATION OF MARTENSITIC-TRANSFORMATION IN FE-NI FACE-CENTERED-CUBIC ALLOYS

The F.C.C. --> B.C.C. martensitic transformation in Fe-Ni alloys containing between 20 and 40 at.% Ni was studied using molecular dynamics simulations. The interatomic interactions were represented using the embedded atom method pseudo-monoatomic potentials, which were shown to represent correctly the relative stability of the F.C.C. and B.C.C. structures as a function of the nickel content. The simulation results dearly demonstrate the important role that crystal defects, such as the free surface or grain boundary, play in the formation of martensite. This is consistent with the experimental observations, which suggest that the martensitic nucleation is of a heterogeneous nature. The simulation results further indicate the need for lattice invariant deformation, such as twinning and slip, for the continued growth of martensite.