MARTENSITIC NUCLEATION MECHANISM

A sort of special dislocation configuration was deformation-induced in an Fe-Ni-V-C alloy by in-situ elongation tests of TEM. The cooling in -situ observations, as well as the SADPs from the region of the specia l dislocation configurations, proved that they are martensitic nuclei. In martensitic transformation, a nucleus changed into a small martens itic sub-plate, and a group of parallel sub-plates that formed from a group of parallel nuclei made up a big martensitic plate. Martensitic transformation involved opposite shear between adjacent martensitic nu clei. By using the reduced-cell method, the crystallographic structure of observed martensitic nuclei was indexed as a face-centered orthogo nal (FCO) lattice, which was explained by the nucleation mechanism pro posed by the present authors. The crystallographic analysis confirmed that the defect faulting involved in martensitic nucleation took place among three close packed planes, instead of between two adjacent plan es as an ordinary stacking fault.