Zirconium alloys : zirconium alloy is a zirconium matrix by adding other elements consisting of non-ferrous alloys.
Profile: Zirconium alloys have good corrosion resistance, moderate mechanical properties, low thermal neutron absorption cross section of atoms (Zr 0.18 barns) at high temperature and pressure water and steam 300 ~ 400 ℃, the nuclear fuel has a good compatibility, and therefore can be used as a water-cooled nuclear reactor core structural material (fuel cladding, pressure pipes, pipe brackets and channel), which is the main use of zirconium alloys. Zirconium on a variety of acid (such as hydrochloric acid, nitric acid, sulfuric acid and acetic acid), alkali and salt have excellent corrosion resistance, it is also used to make corrosion resistant zirconium alloy components and pharmaceutical devices. Zirconium and oxygen, nitrogen and other gases has a strong affinity, the zirconium and zirconium alloys and also electric vacuum bulb industry is widely used as a non-evaporable getter (see getter material). Zirconium has excellent light emission properties, and thus became the flash of fireworks materials.
Development: pure zirconium on its strength and corrosion resistance, it can not meet the nuclear fuel cladding tube and pressure requirements. The late 1940s, the United States in order to explore the application of zirconium in water-cooled reactors, to examine the zirconium-based alloys. By the mid-1950s, it has developed into an excellent overall performance of Zr-2 alloy (Zirca-loy-2), and used as the world's first nuclear submarine "Nautilus" nuclear fuel cladding material number, and later made of Zr-4 ( Zircaloy-4), Zr-1Nb and Zr-2.5Nb alloy. Twenty years, many other countries have also studied the zirconium alloy, but the overall performance as good as the above-mentioned alloy, which is not much use. Currently, from the sponge zirconium to zirconium alloy, it has achieved national industrial production in the United States, Russia, France, Germany, Canada and China.
Category: industrial-scale production of zirconium-based alloys have two series: zirconium and zirconium niobium-tin system. The former representative of the Zr-2 alloy, the latter on behalf of the Zr-2.5Nb alloy. Composition and properties shown in Table zirconium and zirconium alloys of three kinds. Zirconium alloy elements selection principle is: not a significant increase in zirconia thermal neutron absorption cross section; Second, we must not be too damaging to improve process performance zirconium corrosion resistance and strength at the same time. Tin-based alloys zirconium, tin, iron, chromium, nickel added integrated (Zr-2 alloy), may improve the material strength and corrosion resistance, thermal conductivity, corrosion film, reducing the surface state of the corrosion susceptibility; zr-4 alloy does not contain nickel, and appropriate increase in iron content, this hydrogen-absorbing alloy corrosion was only about half of the zr-2 alloy. Zr-2 alloy is usually used for boiling water reactor, Zr-4 alloy used in pressurized water reactors. When the zirconium niobium alloy, the temperature at the solubility limit of α-Zr addition amount of Nb is reached, the best corrosion properties of the alloy. Zr-1Nb and Zr-2.5Nb alloy niobium content is higher than the solubility limit of the use temperature. More than niobium to a supersaturated state is present in α-Zr in the alloy corrosion resistance negatively, while the second phase in the form of β-Nb presence was much better. Most of zirconium and zirconium alloy metal impurity elements required to 50ppm or less, thermal neutron absorption cross section of large elements (such as boron and cadmium) shall not exceed 0.5ppm; nitrogen serious damage to the corrosion resistance of not more than 80ppm; there are some oxygen strengthen the role of its content by the strength requirement is generally 800 ~ 1600ppm.
Shift: zirconium and zirconium alloys have allomorphs change, high temperature phase is the β-Zr body-centered cubic structure, low-temperature phase is a close-packed hexagonal structure of α-Zr. Pure zirconium transition temperature of 862 ℃. Alloys and industrial zirconium transition temperature is influenced by alloying elements and impurities elements: iron, nickel, chromium, niobium added to narrow the α-Zr phase region, so that transformation temperature is lowered; oxygen, nitrogen, tin expand α-Zr phase region, so that transition temperature. Zr-2.5Nb quench hardening alloys have significant effects. This alloy is heated to a zone or beta] (α + β) temperature region, after quenching in water, its room temperature tensile strength of up to 90 kg / mm 2; and then quenching the alloy aged at 500 ℃ appropriate, its strength is not reduced , while the plasticity is significantly enhanced. This solution - aging alloys have excellent corrosion resistance.
Processing: zirconium and zirconium alloy plastic, and can be made into pipe, plate, rod and wire, wherein the pipe as the main products. Processing zirconium and zirconium alloys of zirconium basic nature and depends on the special requirements for nuclear reactors zirconium component. The basic properties of zirconium is: easily contaminated oxygen, nitrogen, hydrogen, etc., easy to stick mold, there allomorphs change. Zirconium nuclear reactor components requires a high dimensional accuracy, microstructure demanding performance and stability. The most widely used seamless zirconium tubes for the main processing steps: preparation of a consumable electrode, casting, forging, hot extrusion (tube), cold, finishing.
Vacuum consumable arc melting method is the most common method of zirconium and zirconium alloys of industrial production. With the correct method of alloying elements, the right mix of old and new material and a reasonable proportion casting system in order to obtain a high quality ingot.
Ingot blooming ships in β phase region, which is conducive to deformation, but also reduce the segregation of alloying elements. Secondary forging temperature is lower than the breakdown, pure zirconium and Zr-2 alloy in the α-phase region temperature zone forging, Zr-2.5Nb in (α + β) phase region forging. Final forging temperature not lower than 700 ℃. Hot rolling temperature and the temperature is similar to the secondary forging, extrusion temperature lower. In order to prevent oxidation and stick mold, prior to extrusion billets to a copper-clad, or add a glass coating. Pure zirconium at liquid nitrogen temperature is still a good plasticity. At room temperature twice the amount of cold-rolled sheet annealing between up to 40% or more. Cold finished before the system has an important impact on the quality and performance of Zircaloy tubing. In order to obtain good overall performance pipe, a total reduction of finished products before cold rolling should be more than 50%.
At room temperature was close-packed hexagonal structure of α-Zr in the cold deformation easy to form texture. Texture zirconium tubes have an important effect on its strength, creep properties, hydrides orientation, irradiation growth, etc. Zr-4 alloy cladding tube reactors in use, usually requires nearly radial textured base (ie, a hexagonal lattice of C axis substantially parallel to the tube diameter). Easy to get this texture than the general orientation when the final cold working step wall thickness to diameter shrinkage rate greater than 1. In the Zr-2.5Nb pressure pipe production by controlling the extrusion process parameters and extrusions organizations to control the texture. Zr-2.5Nb hydride alloys in sheet form randomly oriented, plus the control pressure pipe technology, will enable the sheet hydride was tangential distribution to achieve the desired texture. Cold plate through recrystallization annealing (about 650 ℃) after the texture changes hydride orientation becomes confused (see preferred orientation). Annealed cold material must be conducted in a vacuum oven, the vacuum should be higher than 10-4 Torr. Intermediate annealing temperature of about 700 ℃. Finish annealing is determined according to the performance requirements. The fuel cladding surface is very strict, which normally takes pickling. Pickling solution is an aqueous solution of hydrofluoric acid and nitric acid. Pickling must completely remove the fluoride ion workpiece surface, otherwise it will reduce the corrosion resistance of the material. It must be finished pipe straightening. If the straightening process is inappropriate, it will result in non-uniform mechanical properties, low ductility blasting and hydride orientation disadvantage.
Welding: zirconium and zirconium alloy has good welding properties. Commonly used methods of TIG welding and electron beam welding. Large-diameter thin-walled tube commonly used in welding fabrication. Fenxie flammable zirconium, zirconium during grinding and cutting products to pay attention to safety.
Inspection: In the production of the cladding tube reactor with the pressure tube and in the process, to be very strict inspection. Each batch of products, in addition to routine chemical composition, mechanical properties, dimensional accuracy and corrosion test other items outside of each tube are required by NDT inspection.
Baoji Bo Yang Metal Materials Co., Ltd
Add:Qing Anbao Industurial Park,BaoTi Rord,Gaoxin District,Baoji City,shaanxi,China