Effect of Rolling Speed on Microstructural and Microtextural Evolution of Nb Tubes during Caliber-Rolling Process

Jongbeom Lee,Haguk Jeong

doi:10.3390/met9050500

Abstract

This study investigated the fabrication of Nb tubes via the caliber-rolling process at various rolling speeds from 1.4 m/min to 9.9 m/min at ambient temperature, and the effect of the caliber-rolling speed on the microstructural and microtextural evolution of the Nb tubes. The caliber-rolling process affected the grain refinement when the Nb tube had a higher fraction of low angle grain boundaries. However, the grain size was identical regardless of the rolling speed. The dislocation density of the Nb tubes increased with the caliber-rolling speed according to the Orowan equation. The reduction of intensity for the <111> fiber texture and the development of the <112> fiber texture with the increase of the strain rate are considered to have decreased the internal energy by increasing the fraction of the low-energy Σ3 boundaries.

Highlights

Nb tubes are used in wires made of superconducting materials, such as NbTi, Nb3 Sn, Nb3 Al, and MgB2 /Nb/Cu, as a diffusion barrier for MgB2 /Nb/Cu, which disturbs the chemical reaction between the Mg-B powders and Cu, and as a superconductor for NbTi and Nb3 Sn, which have superconductive properties [1,2,3,4]
To manufacture a superconductive wire without fracturing, it is very important to improve the ductility of the Nb tube such that it can play a role as a diffusion barrier or a superconductive material
This study investigated the effect of the caliber-rolling speed on the microstructural and microtextural evolution of Nb tubes during the caliber-rolling process

Summary

Introduction

Nb tubes are used in wires made of superconducting materials, such as NbTi, Nb3 Sn, Nb3 Al, and MgB2 /Nb/Cu, as a diffusion barrier for MgB2 /Nb/Cu, which disturbs the chemical reaction between the Mg-B powders and Cu, and as a superconductor for NbTi and Nb3 Sn, which have superconductive properties [1,2,3,4]. To manufacture a superconductive wire without fracturing, it is very important to improve the ductility of the Nb tube such that it can play a role as a diffusion barrier or a superconductive material. This can be achieved by using optimal conditions in the deformation process. In previous work on the drawing process [5,6], it was stated that an electric field significantly affects the nature of grain boundaries via a localized Joule heating effect, which was experimentally proved by Zhan et al [7]. The electrically assisted wire drawing process has been proved to be a feasible technique that enhances the material formability compared to the conventional wire drawing process [8]

Methods

Results

Conclusion