Microstructure And Corrosion Resistance Of β Phase Water Quenched Zirconium And Zirconium Alloys

Zr and Zr alloys are used in harsh service environments such as nuclear reactors because of their excellent radiation resistance,corrosion resistance and mechanical properties.With the improvement of power generation efficiency,Zr and Zr alloys must have stronger corrosion resistance.At present,the main methods to improve corrosion resistance include alloying,coating,heat treatment and so on,among which alloying elements are limited by Sn,Nb,Cr,Fe,Mo and other elements due to the requirements of irradiation characteristics,corrosion resistance and mechanical properties.The development and application of coating technology are limited due to technical defects such as pores,cracks and stresses.Heat treatment is a common method to control the microstructure of materials.It is widely used to control the structure and properties of many metal materials.In this paper,the microstructure of Zr,Zr-3 alloys and Zr-4 alloys were regulated by β phase water quenching technology and the effect of quenching treatment on microstructure,oxidation property and corrosion resistance were studied.The structure of Zr-4 alloys were regulated by β phase water quenching process and the effect of quenching on the oxidation resistance of Zr-4 alloys were studied.The microstructure of the recrystallized samples before quenching is characterized by strong(002)texture,equiaemic texture and coarse uniform distribution of second phase particles,while the microstructure of the samples after quenching is characterized by weak(002)texture,lath texture and fine second phase particles distributed along the grain.After oxidation at 400 degrees for 16h,the oxidation weight gain of quenched samples is obviously lower than that of recrystallized samples,showing strong oxidation resistance.The results show that β-phase water quenching reduces the(002)texture strength and makes the easily oxidized(002)crystal surface less exposed on the material surface,which is the main reason for improving the oxidation resistance.The formation of strip grains in quenched samples increases the interfacial content,increases the compressive stress of Zr-4 alloys during oxidation and promotes the formation of tetragonal zirconia.In order to reveal the role of texture in the oxidation process,the molecular dynamics software Lammps was used to simulate the oxidation of different crystal faces of zirconium.The structure of Zr,Zr-3 alloys and Zr-4 alloys was regulated by β phase water quenching technology.The polarization curves and EIS electrochemical impedance spectra of Zr,Zr-3 alloys and Zr-4 alloys were measured by three electrode test method in 3.5 wt.%Nacl electrolyte solution.Compared with the recrystallized samples,the β phase water quenching process can effectively improve the electrochemical corrosion resistance of Zr-4 alloys.The corrosion tendency of Zr and Zr-3 alloys is reduced,but the corrosion current increases after the corrosion of Zr and Zr-3 alloys begins.The improvement of corrosion resistance of Zr-4 alloys can be attributed to the increase of transfer charge resistance due to the weak(002)of quenched alloys and the increase of solid solubility of doped elements.After quenching,the distribution of the second phase particles along grain boundaries reduces the corrosion point location.The reason why the corrosion tendency of Zr and Zr-3 alloys decreases after quenching is that the weak(002)of quenched alloys reduces the corrosion potential and increases the transfer charge resistance.The high corrosion current after corrosion initiation is attributed to the high interfacial volume fraction brought about by the lath texture.