Strengthening of Zircaloy-4 using Y2O3 particles by a laser-beam-induced surface treatment process

The mechanical strength of Zircaloy-4 was enhanced by surface treatment consisting of laser beam scanning of an oxide-coated Zircaloy-4 sheet. An yttrium oxide (Y2O3) coating 7–55μm thick was applied to Zircaloy-4 sheets. Then, a laser beam was used to form a dispersed oxide layer on the Zircaloy-4 metal surface. The thickness of the dispersed oxide layer varied from 80 to 200μm depending on the process parameters. Tensile tests of samples having both surfaces treated were conducted at room temperature and 380°C. The tensile strength of Zircaloy-4 at room temperature was increased by up to 20% with the formation of a thin dispersed oxide layer with a thickness<10% of that of the Zircaloy-4 substrate. However, the tensile elongation of the samples decreased drastically. The decreased ductility became insignificant as the testing temperature increased to 380°C. The strengthening of the fabricated samples could be explained by two mechanisms: (i) oxide particles dispersed in the metallic matrix and (ii) the phase transformation in Zircaloy-4.