Phase transformation temperatures of Zr alloy Excel

Abstract 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 α Zr  + β Zr  → β Zr transus temperature was found to be 968 °C. Also the volume fraction of stabilized β Zr starts to increase in the temperature range of 600–690 °C. Furthermore, it was observed that β Zr does not transform to α ′ -hcp martensite upon quenching from up to a temperature between 846 °C and 864 °C in the α Zr  + β Zr region. Instead, the microstructure of β Zr transforms into a mixture of retained β Zr with a fine dispersion of athermal ω particles and few α″ orthorhombic martensite laths inside the β Zr grains. β Zr was first seen to fully transform to α ’ -hcp martensite after quenching from 864 °C; a drastic increase in the volume fraction of β Zr occurs above this temperature.