Modelling precipitation in zirconium niobium alloys

A model has been developed to predict precipitation of β-Nb in zirconium–niobium alloys. The model considers two transformation mechanisms; in situ transformation of any retained β-Zr and homogeneous nucleation of β-Nb. The two mechanisms are allowed to operate concurrently and compete for the available solute. The model has been calibrated and tested using data in the literature and is able to reasonably reproduce these results without introducing non-physical fitting parameters. It has then been applied to predict the effects of prior β-Zr fraction, oxygen content, and temperature on the precipitation kinetics of β-Nb. These calculations predict that prior β-Zr fraction has a strong effect on the kinetics of subsequent β-Nb evolution and that oxygen content is also critical, with higher oxygen levels predicted to result in faster kinetics and shift in the peak transformation rate to higher temperatures.