There are two series of zirconium-based alloys produced on an industrial scale: zirconium-tin series and zirconium-niobium series. The representative of the former is Zr-2 alloy, and the representative of the latter is Zr-2.5Nb alloy. The composition and properties of zirconium and three zirconium alloys are shown in the table. The selection principle of alloy elements of silicon zirconium is: one can not significantly increase the thermal neutron absorption cross section of zirconium; the second is to improve the corrosion resistance and strength of zirconium while not excessively damaging the process performance. In the zirconium-tin alloy, the combined addition of tin, iron, chromium and nickel (Zr-2 alloy) can improve the strength and corrosion resistance of the material, the thermal conductivity of the corrosion-resistant film, and reduce the sensitivity of the surface state to corrosion; Zr-4 alloy does not contain nickel and increases the iron content appropriately. The corrosion hydrogen absorption of this alloy is only about half of that of Zr-2 alloy.
Usually Zr-2 alloy is used for boiling water reactor, Zr-4 alloy is used for pressurized water reactor. In the zirconium-niobium alloy, when the amount of niobium added reaches the solid solution limit of α-Zr at the use temperature, silicon zirconium has the best corrosion resistance. The niobium content in Zr-1Nb and Zr-2.5Nb alloys is higher than the solid solution limit at the use temperature. Excessive niobium exists in α-Zr in a supersaturated state, which is detrimental to the corrosion resistance of the alloy, but it is much better to exist in the form of the second phase β-Nb. Most of the metal impurity elements in zirconium and zirconium alloys are required to be below 50ppm, and elements with large thermal neutron absorption cross sections (such as boron and cadmium) should not exceed 0.5ppm; nitrogen that seriously damages corrosion resistance should not exceed 80ppm; oxygen has a certain amount According to the strength requirements, its content is generally 800～1600ppm.
