| The effect of cooling rate on the mechanical properties of Zircaloy-4 alloy was studied for the specimens which were heated in the region of βphase and then cooled in various cooling processes, such as, iced brine, water, oil, air and furnace cooling. It was observed that the iced brine and water quenching of the specimens resulted in higher strength and greater strain hardening rate than the oil quenching, air and furnace cooling. It is believed that the increase in the strength and the strain hardening rate is attributed to the increase in stress required to move glide dislocations due to twins and tangled dislocations introduced during the quenching process, i.e., martensitic transformation. It was also observed that the strength and the strain hardening rate were increased gradually as the cooling rate increased from furnace cooling (0.05℃/s) to oil quenching(110℃/s). This means that the two properties are mainly controlled by α-lath size. From the microstructure and hardness, it was shown that the iced brine and water quenched specimens resulted in faster recrystallization than the oil quenched and air cooled specimens. It was suggested that the iced brine quenched specimen was recrystallized through the homogeneous nucleation, while the recrystallization of water quenched specimen seemed to follow the bulge mechanism. |
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