Study On Microstructure And Properties Of Annealed Cold Rolled Zr-Sn-Nb Alloy Stirp

Zr-Sn-Nb alloy is an advanced zirconium alloy with excellent mechanical and corrosion properties under operational conditions and low neutron absorption.That is why it is widely used in the preparation of nuclear fuel assembly for PWR. As the life of nuclear fuel assembly and the reliability of a reactor are related to the microstructure, mechanical properties and antioxidant properties of zirconium alloy, much more research on it should be made. This paper, taking the Zr-1.0Sn-1.0Nb alloy as its subject, mainly studied the forward factors with the method of metallographic, SEM, EBSD, uniaxial tension, cyclic oxidation, etc.The main conclusions of this paper are as follows:(1) Chemical polishing- hot staining method, suitable to the different treatment of zirconium alloy, is effective for preparing metallographic specimen. After cold-rolling and annealing, typical recrystallization annealing microstructure was obtained in Zr-Sn-Nb alloy strip whose grains are equiaxed with an average size of 3.5?m. Many second phases of different size distribute fairly and uniformly in the matrix, besides which, the size of Zr-Nb-Fe particle is larger than that of ?-Nb particle. The ?/(?+?) starts transformating around 600? while the(?+?)/? starts among 800 ?and 900?.(2) Zr-Sn-Nb annealed strip possessed typical basal texture with twin peaks, and [0001] basal poles(in TD-ND plane) titled ±30° in TD. The larger grains mostly belonged to the {0001}< 10(?)0 > and {0001}< 11(?)0 > texture while the smaller ones tended to be the {0001}< 10(?)0 > texture. That was induced by incomplete recrystallization annealing. It illustrated that prolonging annealing promoted {0001}< 10(?)0 > texture turned into {0001}< 11(?)0 > texture.(3) Due to the texture, the annealed strip presented mechanical anisotropy. At 25~400?,the ?s was highest in TD; the ?b was highest in RD and lowest in 45°direction. The elongation was highest in 45°direction and lowest in TD at 25~300? while it was RD and TD accordingly at 300~400?. With temperature increasing, the mechanical anisotropy of Zr-Sn-Nb alloy strip decreased gradually. Dynamic strain aging(DSA) existed from 200? to 400? and was most obvious around 300?.(4) At the temperature from 500 ? to 900?, the oxidation process of Zr-Sn-Nb alloy in air can be divided into three regimes that are pre-breakaway, breakaway and post-breakaway. In all temperature ranges, the weight gain at pre-breakaway regime fitted parabolic rate law. However, the post-breakaway regime conformed to liner or exponential to accelerated law. With temperature increasing, the oxidation rate increased rapidly and the breakaway happened in advanced. At the temperature from 500? to 900?, the breakaway were observed at the time of 1.58×105s, 1.44×104s, 1.15×103s, 9×102s and 6×102s. Oxide volume expansion and crystal transformation attributed to the holes and cracks in oxide film. Finally, it made the breakaway.