Effect of β-Quenching on Oxidation Resistance of Zirconium Alloy ZrNbMoGe for Fuel Cladding Material

Effect of ß-quenching of Zr-2.5Nb-0.5Mo-0.1Ge alloy used for advanced fuel cladding material of Pressurized Water Reactor (PWR) was investigated. The aim of this research is to improve the mechanical and corrosion properties through modification of the alloy with regard to high reactor burn up. The quenching process was conducted by heating the sample at temperature of 950 oC and soaking 2.5 hours, followed by quenching in water at room temperature and then continued with annealing process at 500 and 600oC. The change of hardness and oxidation resistance were characterized using optical microscope and scanning electron microscope (SEM). The effect on the oxidation resistance was investigated by the high temperature oxidation test using the MSB (Magnetic Suspension Balance) at 700 oC for 5 hours. The hardness increased from 217 VHN to 265 VHN after quenching due to grain refinement and precipitation hardening. The oxidation rate followed the typical parabolic growth characteristic. The formation of thin layer was considered to be a stable oxide ZrO2 that influenced the oxidation characteristic and increasing the hardness of the alloy.