Corrosion of Zircaloy-2 Cooled from β Phase Temperature with Different Cooling Rates, in Hot Water and Steam Environment

• Published in: Journal of the Atomic Energy Society of Japan / Atomic Energy Society of Japan Vol. 14; no. 11; pp. 589 - 596
• Main Authors: UEKI, Ichiro, AKIYAMA, Hiroaki, KAGAWA, Masaru
• Format: Journal Article
• Language: Japanese
• Published: Atomic Energy Society of Japan 30.11.1972
• Subjects: alloying element; breakaway; cooling; corrosion; corrosion resistance; grain boundary; intermetallic compounds; oxidation; oxide film; steam; stresses; water; zircaloy; zirconium
• ISSN: 0004-7120; 2186-5256
• DOI: 10.3327/jaesj.14.589

Specimens of the subject material were immersed in water at 360°C under 190kg/cmcm2 and in steam at 400°C under 100 kg/cmcm2 up to 175 days, and their behavior was examined by weight gain measurements and metallographic examination. The results yielded the following information. (1) In the case of as-cooled zircaloy, the effect of differences in cooling rate on the corrosion weight gain is found only in the early stages of steam corrosion, and this is attributed to blistering of the oxide films found between the grain boundaries on the surfaces of the alloy. (2) Preferential oxidation of grain boundaries is found on as-cooled specimens corroded in water, and this is attributed to galvanic-type corrosion accelerated by local dilution of the solute elements around the precipitates on the grain boundaries. (3) The "Breakaway" phenomena in zircaloy corrosion kinetics is explaind in terms of the mechanical detachment of the protective oxide films from the alloy surfaces by stresses which arise during film growth, and rapid propagation of this cleavage favored by the change occasioned on the microstructure of the oxide films. (4) Among the alloying elements of zircaloy-2, Fe, Cr and Ni are found to precipitate with Zr as intermetallic compounds, thus forming discontinuities on the oxide film, and these elements consequently contribute to relieving the stresses and to improving the corrosion resistance of the alloy.