Autowave Criteria of Fracture and Plastic Strain Localization of Zirconium Alloys

Lev B Zuev,Svetlana A Barannikova,Dina V Orlova

doi:10.3390/met12010095

Abstract

Plastic deformation and fracture of Zr–1% Nb alloys exposed to quasi-static tensile testing have been studied via a joint analysis of stress-strain curves, ultrasound velocity and double-exposure speckle photographs. The possibilities of ductility evaluation through the εxx strain distribution in thin-walled parts of zirconium alloys are shown in this paper. The stress-strain state of zirconium alloys in a cold rolling site is investigated considering the development of localized deformation bands and changes in ultrasound velocity. It is established that the transition from the upsetting to the reduction region is accompanied by the significant exhaustion of the plasticity margin of the material; therefore, the latter is more prone to fracture in this zone exactly. It is shown that traditional methods estimating the plasticity margin from the mechanical properties cannot reveal this region, requiring a comprehensive study of macroscopically localized plastic strain in combination with acoustic measurements. In particular, the multi-pass cold rolling of Zr alloys includes various localized deformation processes that can result in the formation of localized plasticity autowaves. Recommendations for strain distribution division over the deformation zone length in the alloy in the pilger roll grooves are provided as well.

Highlights

It is known that the macroscopic localization of plastic flow has an autowave behavior, and the type of autowave is determined by the strain hardening law [1,2]
To improve the quality of products made of zirconium alloys by creating deformation conditions without breaking the continuity of the relevant material, the melted ingot is subjected to hot processing into a workpiece on a screw rolling mill at the equilibrium temperature of beta-zirconium [32]
Nb alloy pilgerheads and demonstrated the ability to reliably control these states in blanks different stages of the manufacture of zirconium alloy

Summary

Introduction

It is known that the macroscopic localization of plastic flow has an autowave behavior, and the type of autowave is determined by the strain hardening law [1,2]. The use of zirconium-based alloys as fundamental structural materials for nuclear reactors [7,8] requires knowledge of their structure and properties during plastic deformation [9] This is of great importance, especially when assessing the technological plasticity of alloys in the manufacturing of finished products. To improve the quality of products made of zirconium alloys by creating deformation conditions without breaking the continuity of the relevant material, the melted ingot is subjected to hot processing into a workpiece on a screw rolling mill at the equilibrium temperature of beta-zirconium [32]. It should be noted that the traditional methods of determining the plasticity in different zones of the rolling center based on the mechanical properties do not provide a reliable assessment due to the macroscopic localization of plastic deformation during any shaping process

Materials and Methods

Findings

Discussion owing to the heterogeneity of the forged billet structure revealed

Conclusions