The effects of alloying elements and heat treatment on nodular corrosion resistance of zirconium alloys

The effects of alloying elements and heat treatment condition on nodular corrosion of zirconium binary alloys were investigated by short term autoclave tests at 500 C. Sheet samples of various zirconium alloys were prepared, and solution treatments from several temperatures were performed. The transition elements, i.e, chromium, iron and especially nickel, exhibited pronounced effects on the improvement of nodular corrosion resistance with increasing concentration. The important corrosion reduction role of nickel addition was observed above 0.01 % concentrations. The frequency and severity of nodular formation of Zr-Sn Alloys were extremely decreased at a 3 % tin content. In the range of tin contents for zircaloy specifications, a slight degrading effect was observed. Solution treatments affected the corrosion properties of these alloys. A high cooling rate from the beta phase or arpha+beta phase temperatures led to low nodular corrosion sensitivity. A smaller quantity and more uniform distribution of fine intermetallic particles were obtained by rapid cooling in comparsion with slow cooling, although chemical composition and crystal structure were not affected by cooling rate. It is considered that nodular corrosion resistance may be improved as the supersaturation quantity of these elements in the alpha-Zr matrix increases. (author)