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.