Bulk and surface defects in fatigued Cu-Zn-Al single crystals

M. SADE, J. MALARRIA, A. YAWNY, F.C. LOVEY

Wisla

Conferencia; XVIII Conference on Applied Crystallography; 2001

The martensitic transformation is often accompanied by the production of defects either in the austenite, the martensite or in both phases. An interesting example of this is the generation of bulk dislocations and surface defects after pseudoelastic cycling in Cu-Zn-Al single crystals. The involved phases are the cubic (L21) of the austenite and the monoclinic 18R martensitic phase. The dislocations arrange in the bulk following crystallographic patterns associated to the habit plane of the transition and the basal plane of the martensite. A microscopic analysis shows that the dislocations are produced by plastic deformation of the martensite. These dislocations have several consequences on the mechanical behavior of the material and on the kinetics of the diffusional processes present in both phases. The formation of intrusions and extrusions at the surface specimens is another important effect of the pseudoelastic cycling. They play a crucial role on the fatigue life of the specimens. Recent results show a strong effect of composition on the nucleation of surface defects. The crystallography of the defects, the origin of the dislocations, their arrangements and their interaction with the specimen surface are discussed.