LOW ENERGY DISLOCATION STRUCTURES DUE TO FATIGUE SOFTENING

The evolution of dislocation structures in 6% prestrained steel 1018 during fatigue has beenstudied by TEM.The dislocations are quite movable,the loose cells quickly change to“checkboard”structures,in which the main cell walls lie about {100}.Then,the low energydislocation structures i.e.dipolar walls and abyrinth structures are evolved.The characteristicof labyrinth and the orientation of dipolar walls are quite similar to fcc crystal.This indicatesthe energy state of system and the moving ability of dislocations are important factors affect-ing softening process,rather than the slip geometric characteristic of dislocations and detailsof dislocations.The decreasing in misorientation between adjoining cells and internal stressare discussed.