Effect of laser surface heat treatment on the oxidation behavior of zircaloy-4

The effect of heat treatment on the oxidation behavior of Zircaloy-4 plates was investigated in 400 to 600deg C steam for alpha-annealed, beta-quenched, and laser surface beta-treated samples. It was observed that the laser treatment resulted in the formation of surface layer of 40∼50μm thick beta-treated structure on the mass of alpha-annealed plates, and the microstructure of laser treated layer was much finer than those of alpha-annealed and beta-quenched samples. The corrosion resistance of laser treated Zircaloy was found to be superior to other two samples in all the temperatures. At 600deg C, the corrosion rate was changed from cubic (W=kt1/3) to linear rate (W=kt) after about 7 hour exposures. The marked improvement in corrosion resistance of laser treated samples is thought to be due to the change of the second phase particle distribution. The coarse and discrete particles in the alpha-annealed structure changed to the fine and chain-like particles in the laser heat treated samples. In this study, the structure of oxide layer was observed to be only one type of monoclinic ZrO2. (Author)