Effect of quenching rate on the β-to-α phase transformation structure in zirconium alloy

Microstructures of low-tin Zircaloy-2 specimens subjected to quenching from β to α phase have been studied using optical and scanning electron microscopy (SEM). The specimens were quenched at different cooling rates ranging from 3 to 83 K s−1. Optical microscopy (OM) provided data on the α phase plate width which is correlated to the cooling rate. All the obtained structures after quenching indicate basket-weave morphology. In addition, OM furnished information on β phase grain size which is correlated to the holding time in β phase prior to quenching. SEM was used to characterise the second phase particles in regard to size distribution and mean size in two of the specimens quenched at the rates of 58 and 6.6 K s−1. One of the specimens was annealed in the α phase after β-quenching, upon which particle sizes were measured. Physical-based models are used to evaluate and explain the microstructural properties observed in this experiment.