Screw dislocation assisted martensitic transformation of a bcc Cu precipitate in bcc Fe

Abstract

Molecular dynamics simulations of the interaction between a screw dislocation and a coherent bcc Cu precipitate in bcc Fe indicate that the screw dislocation stress field assists a martensitic transformation into a close-packed structure for precipitate diameters larger than 1.8 nm, resulting in a stronger obstacle to dislocation glide. The observed martensitic transformation mechanism agrees with the Nishiyama-Kajiwara [Jpn. J. Appl. Phys. 2, 478 (1963)] model. For coherent bcc Cu precipitates with diameter larger than 2.5 nm, the screw dislocation bypass mechanism becomes Orowan looping due to the coherency loss of the precipitates during the transformation. (c) 2007 American Institute of Physics.