Microstructural evolution of α or β quenched zirconium alloys during isothermal agings, between 20 °C and 750 °C

Abstract
In Zircaloy and zirconium alloys, after quench from the upper limit of the α domain a small quantity of iron, chromium or nickel remains in solid solution and then precipitates during further isothermal aging. This precipitation is studied between 450°C and 600°C, using thermoelectric power (TEP) and resistivity measurements. It is shown that precipitation kinetic is strongly reduced by the presence of oxygen and tin. After quench from the β domain (1030°C) five stages of evolution are detected by TEP measurements in Zircaloy-4, the more important being : - a low temperature evolution (<400°C) attributed to local atomic rearrangements - the precipitation of iron and chromium initially dissolved. The amplitude of TEP variation shows that β quench do not permit to allow larger amount of iron and chromium in solution tha for α quench - the recrystallization of the initial martensitic structure.