An electron-microscopy study of dislocation structures in fatigued Cu-Zn-Al shape-memory alloys

Abstract

Samples of Cu-Zn-Al shape-memory alloys have been fatigued by stress cycling through the martensitic transformation. The structure of the dislocations formed after fatigue was investigated by transmission electron microscopy. The dislocations are found to be accumulated in bands closely parallel to those of either the habit plane or the basal plane of the induced variant of martensite. The Burgers vectors of the dislocations are analysed by a computer-simulation technique. Most of the dislocations are of mixed character (u = <111>, b = <001>). Among these dislocations, those gliding on the (101) plane, which is transformed into the basal plane of the induced martensite, are clearly predominant. Several proposed models for the formation of dislocations during the fatigue testing are critically reviewed.