In recent years, the requirements of reactor burnup and refueling cycle are gradually increasing, which requires further improving the mechanical strength and water or steam corrosion resistance of cladding materials within 360~400℃. Therefore, high-performance
zirconium alloys have been developed vigorously. Since the 1980s, a series of new zirconium alloys have been introduced successively. On the basis of Zr-4, China has developed new zirconium alloys such as N18 and N36, which have corrosion resistance, hydrogen absorption and mechanical properties greatly improved by adjusting the composition.
Due to the limited alloying elements that can be used as nuclear zirconium alloys, the main alloying elements added in zirconium alloys are
Nb, Sn, Fe, Cr, V, Cu,
Mo, Al, etc. Studies have shown that
molybdenum has a strong strengthening effect on zirconium alloys. It is reported that the yield strength can be increased by 20% by adding 0.3%~0.5%(mass fraction) of Mo. The high melting point precipitation phase ZrMo2 and Laves phase can be obtained by adding Mo. The high melting point second phase can avoid or reduce the phenomenon that the corrosion resistance of zirconium alloy is affected by the growth of the second phase during the processing and reprocessing of zirconium alloy under the existing process. Therefore, it is of great theoretical and practical significance to study the effects of Mo addition on the microstructure, corrosion resistance and high temperature mechanical properties of zirconium alloys.
A proper amount of Mo in zirconium alloy can stabilize β phase, refine the lat structure, refine the grain size and form fine and dispersed Laves phase. Such microstructure characteristics can hinder the generation of twins and weaken the substrate texture, thus improving the yield strength and high temperature creep resistance of zirconium alloy and the key corrosion resistance of the material. Therefore, adding Mo is an important way to improve the mechanical properties and corrosion resistance of existing zirconium alloys. At present, the research on the effects of Mo on the mechanical properties, recovery, recrystallization and corrosion properties of zirconium alloys is not systematic and mature. For example, the types of alloys studied are few, and the strengthening mechanism, recrystallization mechanism and corrosion resistance mechanism are not clear, so it is urgent to carry out further basic research.
