High-resolution electron microscopy observations of transient lattices from fcc to bcc at the austenite martensite interface

Atomic arrangements of austenite fcc and martensite bcc near the interface in an Fe Ni Mn alloy have been observed by high-resolution electron microscopy. It is found that atom rows along the close-packed directions of two phases are completely coherent at the interface, but there exist deformed lattices which are neither fcc nor bcc. These lattices are regarded as transient lattices changing continuously from fcc to bcc lattice. By observation of these transient lattices we can deduce the lattice deformation in the fcc to bcc martensitic transformation. It is concluded that the lattice deformation proposed by Kurdjumow and Sachs is perfectly consistent with the observed atomic arrangements near the interface. The Bogers and Burgers mechanism is inadequate to explain the present observations. It is emphasized that the austenite martensite interface in the present alloy is not a monoatomic layer but has a width of about 0 7 nm in which the transient lattices are contained.