Embedded atom computer simulation of lattice distortion and dislocation core structure and mobility in Fe-Cr alloys

The atomistic structure of dislocation cores of[111] screw dislocations in disordered Fe-Cr b.c.c. alloys was simulated using embedded atom method potentials and molecular statics computer simulation. The mixed Fe-Cr interatomic potentials used were derived by fitting to the thermodynamic data of the disordered system and the measured lattice parameter changes of Fe upon Cr additions. The potentials predict phase separation as the most stable configuration for the central region of the phase diagram. The next most stable situation is the disordered b.c.c. phase. The structure of the screw 1/2 [111] dislocation core was studied using atomistic computer simulation and an improved visualization method for the representation of the resulting structures. The structure of the dislocation core is different from that typical of 1/2 [111] dislocations in pure b.c.c. materials. The core structure in the alloy. tends to lose the threefold symmetry seen in pure b.c.c. materials and the stress necessary to initiate dislocation motion increases with Cr content. The mobility of kinks in these screw dislocations was also simulated and it was found that while the critical stress for kink motion in pure Fe is extremely low, it increases significantly with the addition of Cr. The implications of these differences for mechanical behavior are discussed.