Microstructure and mechanical evolution of FeCrAlMo-xZr fuel cladding alloys during hot corrosion

The microstructural and mechanical evolution of the Fe-13Cr-6Al-2Mo-xZr (x = 0.15, 0.5, 1.0 wt%) alloys for fuel cladding throughout various hot corrosion processes, such as thermal aging at 475 °C in air and high temperature oxidation at 1200 °C under an atmosphere of Ar + water vapour, were investigated. The findings indicate that as the Zr content increases, the grain size of the alloys becomes progressively smaller. During thermal aging, the secondary Laves phase precipitated within the grains and Mo segregation occurred on the grain boundaries, ultimately forming the μ phase. The plasticity decreased by degrees with aging time due to the formation and growth of precipitates, while the tensile strength increased only during the early aging period and then remained almost unchanged. The steam oxidation rate was promoted with the Zr content because of the smaller grain size and the deeper internal oxidation resulting from the faster diffusion of oxygen in ZrO₂ than that in Al₂O₃.