Phase transformation temperatures of Zr alloy Excel

The transformation temperatures of Zr alloy Excel (Zr-3.5%Sn-0.8%Nb-0.8%Mo) pressure tube material were studied using electron microscopy and a quantitative metallography technique. The αZr + βZr → βZr transus temperature was found to be 968 °C. Also the volume fraction of stabilized βZr starts to increase in the temperature range of 600-690 °C. Furthermore, it was observed that βZr does not transform to α′-hcp martensite upon quenching from up to a temperature between 846 °C and 864 °C in the αZr + βZr region. Instead, the microstructure of βZr transforms into a mixture of retained βZr with a fine dispersion of athermal ω particles and few α″ orthorhombic martensite laths inside the βZr grains. βZr was first seen to fully transform to α'-hcp martensite after quenching from 864 °C; a drastic increase in the volume fraction of βZr occurs above this temperature.