Microstructural and Texture Evolution in Pure Niobium during Severe Plastic Deformation by Differential Speed Rolling.

Sang Yong Park,Woo Jin Kim

doi:10.3390/ma15030752

Sang Yong Park, Woo Jin Kim

Open Access

https://doi.org/10.3390/ma15030752

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Abstract

The evolution of the microstructure and texture in body-centered cubic (BCC) niobium (Nb) during conventional rolling and high-ratio differential rolling (HRDSR) at room temperature were compared. More effective grain refinement of the initial microstructure through continuous dynamic recrystallization (CDRX) occurred in the samples processed by HRDSR, but the overall degree of grain refinement was small, despite having undergone severe plastic deformation due to the low rate of CDRX. CDRX more preferentially proceeded on {111}<uvw> γ-fiber grains than on {001}<110> α-fiber grains. The HRDSR-processed samples exhibited weaker α-fiber and stronger γ-fiber than the conventionally processed samples, which indicates that the high shear deformation induced by HRDSR discourages the development of α-fiber while promoting the development of γ-fiber. The HRDSR processed Nb showed a high tensile strength of 450 MPa, and the major strengthening mechanism for the HRDSR-processed Nb was dislocation-density strengthening at large thickness reductions.

Highlights

Niobium (Nb) has a body-cubic centered (BCC) structure and a very high melting point (2741 K)
This study aims to examine the effect of Severe plastic deformation (SPD) via HRDSR on the microstructure, texture, and mechanical properties of pure Nb and determine the relationship between microstructural parameters and strength
Low-angle grain boundaries (LAGBs) are dominant, but the fraction of high-angle grain boundaries (HAGBs) is higher in the samples processed by HRDSR

Summary

Introduction

Niobium (Nb) has a body-cubic centered (BCC) structure and a very high melting point (2741 K). Niobium is scientifically and practically important, since it is the main element of Nb3 Sn- and NbTi-based superconductors [1,2]. Pure Nb has a very low strength, so its application is limited. The strengthening of pure Nb through microstructural refinement is of interest because high-strength Nb can be applied to fabricate special superconducting components where alloying should be avoided [3]. Cold rolling has been used to refine the microstructure of pure Nb [4,5]. Sandim et al [5]

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