Role of solute segregation on microstructure and mechanical properties of Zircaloy-4

The microstructure of two different lots of Zircaloy-4 was investigated by using a scanning electron microscope (SEM) attached to an energy dispersive system (EDS). The alloy containing Ni higher than the ASTM specification shows parallel plate structure with segregation of Ni, Fe, and Cr at the triple points of beta-grains, and it failed during forging due to crack initiation. The second alloy having Ni content within the ASTM specification has basketweave morphology with minute segregation of Fe and Cr and was forged successfully. The absorbed energy is higher for the successfully forged alloy than for the alloy that failed during forging. It was also observed that the fracture started from the segregated area rich in Ni, Fe, and Cr, and propagated along the plate. The alloy with parallel plate structure is harder than the alloy with basketweave structure.