EFFECT OF SEVERE-COLD-WORKING ON MICROSTRUCTURE OF ZIRCALOY 2

摘要

Zircaloy 2 severely cold-worked by face milling or high pressure torsion processing was investigated by microstructural observation using TEM and SEM and by high temperature water corrosion test to make clear the effect of severe cold-working on the microstructure and the corrosion behavior. The Zircaloy 2 showed a microstructure of fine grains of about 100 nm in diameter or high-density defects. Additionally, non-crystalline dense regions of solute elements were observed, however precipitates of intermetallic compounds were hardly observed in the microstructure. The precipitates appeared when the HPT-processed Zircaloy 2 was heat-treated above 673 K. Thus, this change probably indicates that severely cold working causes a structural change from crystalline precipitates to an amorphous state. The corrosion behavior of severely cold-worked Zircaloy 2 in oxygenated high-purity water at 561 K seemed to depend on surface conditions such as residual stress, grain size, and the morphology of precipitates.