High cycle fatigue properties and microstructure of zirconium and zircaloy-4 under reversal bending

Fatigue lifetime curves of a commercial-purity zirconium and zircaloy-4 were measured under reversal bending. Scanning electron microscopic examination on surfaces of fatigued specimens shows that zirconium displays planar slip, whereas zircaloy-4 displays wavy slip. Fracture surface analysis shows that many fatigue striations with a considerable number of micro-cracks are the primary characters in zirconium and zircaloy-4. Fatigue crack generally nucleates in persistent slip bands and twin–matrix interfaces. One set of stacking fault clusters was detected in zirconium. The stacking fault interface is the feeble barrier to dislocation motion. The typical fatigue dislocation configuration is the dislocation walls apparently parallel to the trace of the prismatic plane, which are separated by long straight screw dislocations perpendicular to walls in the commercial-purity zirconium, and also in zircaloy-4, whereas, zircaloy-4 is easier to cross-slip in comparison with zirconium. Several twins and their fine structures were detected in zirconium and zircaloy-4. The relations between twinning, cracking and slip are discussed.