Abstract
The stability of precipitates in Zr–2.5Nb–0.5Cu alloy under heavy ion irradiation from 100 °C to 500 °C was investigated by quantitative Chemi-STEM EDS analysis. Irradiation results in the crystalline to amorphous transformation of Zr2Cu between 200 °C and 300 °C, but the β–Nb remains crystalline at all temperatures. The precipitates are found to be more stable in starting structures with multiple boundaries than in coarse grain structures. There is an apparent increase of the precipitate size and a redistribution of the alloying element in certain starting microstructures, while a similar size change or alloying element redistribution is not detected or only detected at a much higher temperature in other starting microstructures after irradiation.
Highlights
The stability of precipitates is crucially important when assessing the mechanical properties and corrosion behavior of reactor materials
Nagase and Umakoshi [29] reported that the Zr2 Cu phase became amorphous at room temperature and is crystalline at 320 ◦ C under electron irradiation in a melt-spun Zr66.7 Cu33.3 alloy; this is lower than the transformation temperature of 200 ◦ C in our study
The critical transformation temperature for electron irradiation is expected to be much lower than that for ion irradiation because the electron irradiation produces Frenkel pairs, chemical disorder is homogeneously distributed in the intermetallic precipitate, while ion irradiation produces point defects clustered in collision cascades [4]
Summary
The stability of precipitates is crucially important when assessing the mechanical properties and corrosion behavior of reactor materials. It is known that irradiation has a remarkable effect on precipitate stability. It may cause the dissolution, precipitation, growth, and/or amorphization of precipitates, the redistribution of alloying elements, and other associated microstructural changes. In Zr–Nb alloys, the dissolution of Nb and the redistribution of Fe are clearly observed under higher dose irradiation (>3 dpa) [3,7]. These changes will affect the material performance in the reactors such as corrosion behavior and irradiation growth. In Zr–Nb alloys, the super-saturation of Nb in the matrix was demonstrated to degrade corrosion resistance; a full precipitation of β–Nb either from α–Zr or β–Zr is recommended [10,11,12]
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