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The intermetallic precipitates in Zircaloy are generally considered to be of special importance for the properties of the alloy. However, basic feature of the precipitate formation, such as the solubility limits of iron and chromium in a ZrSn matrix, are still unknown. Investigations have been performed with the objective to (1) determine the solubility limits of iron and chromium in a Zr 1.4% Sn matrix, (2) characterize the precipitates formed when the maximum solubility is exceeded, and (3) study the growth mechanism of precipitates in alloys with different (iron + chromium) content. Zirconium base alloys with 1.4% tin and 40- to 16 000-ppm iron or chromium, or both, with varying Fe/Cr ratios have been melted. Sheet specimens have been fabricated and heat treated at temperatures in the range of 550 to 1050°C. The maximum solubility of iron and chromium was found to be very low. The solubility range extends up to 120 ppm for iron at 820°C, 200 ppm for chromium at 860°C, and about 150 ppm for iron + chromium, with Fe/Cr = 2, at 810°C. In the case of iron added to the ZrSn matrix, Zr3Fe precipitates are preferentially formed, with the possible presence of some Zr2Fe particles. After an addition of chromium, the ZrCr2 phase precipitates. Zr(Cr,Fe)2 particles are formed in the presence of iron + chromium. They have the structure of ZrCr2, and a composition ratio Fe/Cr close to the nominal composition of the alloy. If the Fe/Cr ratio exceeds 4, the iron forms additional precipitates as Zr3Fe and Zr2Fe. The size distribution of the particle diameter has been compared with different growth models (Kahlweit theory). The experimental data agree well with a second order kinetic law. The precipitate volume grows as a linear function of time. No systematic influence of a (iron + chromium) content on the modal particle size has been found in alloys up to 15 000 ppm (iron + chromium).

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