MICROSTRUCTURAL EVOLUTION OF BETA-QUENCHED ZIRCALOY-4 DURING AGINGS BETWEEN 100-DEGREES-C AND 750-DEGREES-C

Thermoelectric power measurements (TEP) are used to study the microstr uctural evolution of beta-quenched Zircaloy-4 samples during isotherma l agings between 100 and 750-degrees-C. Five characteristic stages of evolution have been found and their existence confirmed by complementa ry observation techniques (microhardness, electrical resistivity, opti cal and electron microscopy). Segregation of solutes occurs at low tem perature (stage 1). The main microstructural evolutions observed are p recipitation (stage 2) and recrystallization of the basket-weave beta- quenched structure (stage 3). A complete time-temperature transformati on diagram between 20 and 750-degrees-C and for aging times up to 5 x 10(4) min has been drawn allowing a general view of the microstructura l evolutions of Zircaloy-4 in that temperature and time domain.