The Influence of the High Temperatures Thermal Shocks on the Microstructure and Harness of Zircaloy-4 alloy

Abstract

This study aims at determining the influence of thermal shocks at high temperatures, over the allotropic temperature, on the microstructure, composition and hardness of the Zy-4 sheath. The thermal shocks have been applied at the temperatures between 900 and 1600�C, in the air, lasting 30 and 60 s, through rapid heating in the solar furnace. The treated samples were microstructurally analyzed on the surface and in section by scanning electron microscopy and EDS, thickness measurement of the formed layers, the oxygen and hardness profile determination in section relative to the treated surface. At the microstructural level, the researches have revealed the evolution of the morphology of the oxide layers formed under high temperature thermal shock conditions and the evolution of the microstructure of the metallic mass as the temperature and shock duration increase, correlating this evolution with the oxygen diffusion process and with the evolution of the microhardness. Researches have provided information on the Zy-4 alloy behaviour under accidental conditions.