Research on Precipitation Behavior and Mechanism of N36 Zirconium Alloy by Equal Channel Double Angular Pressing and Heat Treatment

Abstract:

Thermoforming treatment is an effective method to refine the precipitate size of N36 alloy, promote its dispersion distribution, and improve its service performance in nuclear reactor cladding materials. In this study, Zr-Sn-Nb-Fe (N36) alloy subjected to 4 passes of equal channel double angular pressing (ECDAP) at 450 ℃ for large deformation and aging treatment at 580 ℃ for 4–8 h. The microstructures were characterized by optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). The results show that aging treatment promotes the precipitation of (Zr,Nb)₂Fe precipitate phase particles, and after aging treatment at 580 ℃ for 4–8 h, the average size of the precipitate phase particles in the initial sample increases from 76 mm to 88 mm. The average size of precipitate phase particles in the samples after 4 passes of deformation increases from 41 mm to 51 mm, and a certain amount of (Zr,Nb)₂Fe phase with a size of 20–40 nm is precipitated. ECDAP sample contains a large number of dislocations and defects, which provide nucleation points for the precipitation of precipitate phase particles during subsequent aging treatment and a short diffusion channel for alloying elements, thereby promoting the fine dispersion and precipitation of precipitate phase particles. This study provides new ideas for improving the comprehensive performance of N36 alloy.