Growth behavior study of second phase particles in a Zr-Sn-Nb-Fe-Cr-Cu alloy

The growth behavior of the second phase particles (SPPs) in a Zr-Sn-Nb-Fe-Cr-Cu alloy during aging (600-700 °C, 30-1800 min) has been investigated using scanning electron microscopy (SEM) and an image analysis technique. Microstructural observations show that the precipitated SPPs distribute linearly along the boundaries of α plates at the initial aging stage. As the aging time prolongs and/or temperature increases, the linear distribution feature of SPPs weakens gradually and finally a random distribution is formed. A numerical analysis confirms that the growth of SPPs follows well the second order kinetics of Kahlweit theory and the activation energy is experimentally determined to be 194 kJ/mol. The reason for the larger growth activation energy of the SPPs in the experimental alloy, compared to that in Zircaloy-4, is discussed and ascribed to the addition of Nb element.