Growth kinetics of second phase particles in N36 zirconium alloy: Zr–Sn–Nb–Fe

Abstract

Analyzing the diffusion kinetics behavior that leads to precipitates formation can assist in understanding the properties of Zr alloy materials. In this study, coarsening growth kinetics of precipitates in N36 zirconium alloy with Nb dominant are experimentally calculated during the isothermal and isochronal aging process (580 °C–700 °C, 0.5–30 h respectively). Microstructure observation and the second phase particles (SPPs) have been investigated and numerically extracted through several processes, including the use of an optical microscope (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), in addition to image software tools. Conclusions confirm that as the temperature or aging period increases, the SPPs begin to lose fine and linear distribution properties ranging from α-plate grain boundary to the random distributions. Moreover, the small particles dissolve, whereas the large ones grow, accurately pursuing the Ostwald ripening property. Besides, most SPPs are found to be in the form of Zr(Nb, Fe)2, and some of them are (Zr,Nb)2Fe. The activation energy of kinetic growth of precipitates has been experimentally calculated using Kahlwiet second-order kinetics and found to be 206 kJ/mol. Compared to other documented Zr-alloy series, we have noticed that the different types of SPPs and the Nb element content in most contribute greatly to the slow diffusion rate, explaining the higher value in the activation energy of the precipitates growth process.