There are two series of zirconium base alloys produced on an industrial scale: zirconium tin series and zirconium niobium series. The former is represented by zr-2 alloy and the latter by zr-2.5Nb alloy. The composition and properties of zirconium and three zirconium alloys are shown in table. The alloying element selection principle of zirconium is as follows: one cannot significantly increase the thermal neutron absorption cross section of zirconium; Second, to improve the corrosion resistance and strength of zirconium while not too much damage the process performance. In zirconium tin alloys, the comprehensive addition of tin, iron, chromium and nickel (zr-2 alloy) can improve the strength of materials, corrosion resistance, corrosion resistance film thermal conductivity, reduce the surface state of the sensitivity to corrosion; There is no nickel in zr-4 alloy, and the content of iron is increased appropriately.
Generally, zr-2 alloy is used for boiling water reactor and zr-4 alloy is used for pressurized water reactor. In the zirconium niobium alloy, the corrosion resistance of the alloy is the best when the niobium content reaches the solution limit of -zr at the service temperature. The content of niobium in zr-1nb and zr-2.5Nb alloys is higher than the solution limit at the service temperature. The excess niobium exists in the -zr in the supersaturated state, which is unfavorable to the corrosion resistance of the alloy, while the second phase is much better in the form of -nb. Most metal impurities in zirconium and zirconium alloys are required to be less than 50 PPM, and elements with large thermal neutron absorption cross sections (such as boron and cadmium) are not allowed to exceed 0.5 PPM. Nitrogen which seriously damages corrosion resistance shall not be higher than 80 PPM; Oxygen has certain strengthening effect, and its content is generally 800 ~ 1600 PPM according to the strength requirement.
Effect of tin content on mechanical and corrosion properties of zirconium - tin alloys. The results showed that the strength of the alloy increased with the increase of tin content in the range of 0.5 wt % ~ 1.7 wt %, and the corrosion gain decreased with the decrease of tin content in the alloy and the anti-furfury-like corrosion ability of the alloy was improved in the vapor corrosion test at 400℃.
