Tensile Strength of Surface-treated Zircaloy-4 with Y₂O₃ Particles using a Laser Beam

Korea Atomic Energy Research Institute (KAERI) is one of the leading organizations for developing ATF claddings. One concept is to form an oxidation-resistant tolerant fuel (ATF) cladding is being developed globally after the Fukushima accident with the demands for the nuclear fuel having higher safety at normal operation conditions as well layer on Zr cladding surface. The other is to increase high-temperature mechanical strength of Zr tube. The oxide dispersion strengthened (ODS) zirconium was proposed to increase the strength of the Zr-based alloy up to high temperatures. The ODS treatment on the Zr surface layer was successfully performed using a laser beam scanning (LBS) process, as shown in Fig. 1. High-power laser beam was exposed on the zirconium surface previously coated by oxides – typically Y₂O₃. The dispersed oxide layer was formed by the penetration of oxide particles into Zr alloys. According to our previous investigations, the tensile strength of Zircaloy-4 was increased by up to 20% with the formation of a thin dispersed oxide layer with a thickness less than 10% of that of the Zircaloy-4 substrate. However, the tensile elongation of the samples decreased drastically. The oxide dispersion strengthened (ODS) layer increased the mechanical strength of Zircaloy-4. The tensile strength of Zircaloy-4 increased by 10-20% with the formation of the dispersed oxide layer. The strengthening of Zircaloy-4 by the ODS layer was very effective at elevated temperature. The brittle fracture observed at room temperature was changed in ductile at elevated temperatures.