Understanding solid-solid (fcc → ω + bcc) transition at atomic scale

Abstract

An atomic transition model of a face-centered cubic (fcc) crystal to a primitive hexagonal x and body-centered cubic (bcc) structures has been crystallographically built. The fcc structure can transform into the x structure through a local shuffling or displacement of atoms about 0.4014 A in iron for afcc iron = 3.59 A . The bcc structure can form either after the x formation or concurrently by the similar mechanism, or the x structure can be treated as an intermediate stage during the transition of fcc → bcc. Such a transition (fcc → ω bcc transition) can be confirmed by Widmanstatten pattern formed in an iron meteorite, pearlitic structure and martensite composed of bcc-ferrite and ultra-fine x particles in iron-carbon steels. The present fcc-bcc orientation relationship matches with Pitsch's one.