HRTEM Study of the {252} sub gamma Austenite--Martensite Interface in an Fe--8Cr--1C Alloy

High-resolution transmission electron microscopy has been used to image the atomic structure of the (252) sub gamma austenite--martensite interface. By imaging along (101) sub gamma || (111) sub alpha the interface was viewed edge-on and seen to consist of facets on the close-packed (111) sub gamma planes. From the correspondence of atoms in the close-packed planes across the austenite--martensite interface, the magnitude of the shear can be analysed as (a/24) < 112 > on every close-packed plane in the plane of projection. Comparison with theory indicates that this is an (a /12) < 112 > Burgers vector out of the plane of projection. Hence, each atomic facet can be viewed as a structural ledge containing an (a/12) < 112 > transformation dislocation. 14 ref.--AA