MICROSTRUCTURAL EVOLUTION OF ALPHA OR BETA QUENCHED ZIRCONIUM ALLOYS DURING ISOTHERMAL AGINGS, BETWEEN 20-DEGREES-C AND 750-DEGREES-C

In Zircaloy and zirconium alloys, after quench from the upper limit of the a 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 degrees C and 600 degrees 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 beta domain (1030 degrees C) five stages of evolution are detected by TEP measurements in Zircaloy-4, the more important being : a low temperature evolution (<400 degrees C) attributed to local atomic rearrangements the precipitation of iron and chromium initially dissolved. The amplitude of TEP variation shows that beta quench do not permit to allow larger amount of iron and chromium in solution tha for alpha quench the recrystallization of the initial martensitic structure.