Improving Texture and Microstructure Homogeneity in High-Purity Ta Sheets by Warm Cross Rolling and Annealing

Doudou Long,Yahui Liu,Shiyuan Zhou,Xiaoli Yuan,Jialin Zhu,Shifeng Liu,Dmytro Orlov

doi:10.3390/met11111665

Doudou Long, Yahui Liu + Show 5 more

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https://doi.org/10.3390/met11111665

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Abstract

The evolution of texture and microstructure uniformity in high-purity tantalum (Ta) sheets during 135° warm cross rolling (WCR) was analyzed in detail. X-ray diffraction suggested that relatively uniform ‘ideal’ deformation texture distribution across the thickness could be obtained from WCR, since more potential slip systems could be activated. Electron backscatter diffraction (EBSD) results indicated that the change in strain path in warm rolling could enhance dislocations mobility and increase the probability of dislocations rearrangement and annihilation. Thus, the proportion of low-angle grain boundaries was significantly reduced, and more sub-grain boundaries or sub-grains were formed via WCR. The calculation of geometrically necessary dislocation density based on the strain gradient model supports this result. The analysis of relative Schmid factor combined with the strain contouring map indicated that inhomogeneous orientation-dependent grain subdivision could be effectively weakened, and relatively uniform strain distribution could be formed in the WCR sample. Upon annealing, uniform fine grain size and more randomly oriented grains were obtained in the WCR sample after the completion of recrystallization because of relatively uniform grain subdivision and stored energy distribution.

Highlights

High-purity Ta with a body-centered cubic structure has attracted more and more attention in the field of sputtering targets owing to its high conductivity, thermal stability, high melting point and excellent corrosion resistance [1]
Homogeneous microstructure, i.e., fine uniform grain size and random crystal orientation, of a high-purity Ta target can significantly improve the uniformity of sputtering film [2,3,4]
Ta ingots prepared by Electron beam melting (EBM) have significant weaknesses including coarse grain size and extremely strong texture [6,7,8]

Summary

Introduction

High-purity Ta with a body-centered cubic (bcc) structure has attracted more and more attention in the field of sputtering targets owing to its high conductivity, thermal stability, high melting point and excellent corrosion resistance [1]. Homogeneous microstructure, i.e., fine uniform grain size and random crystal orientation, of a high-purity Ta target can significantly improve the uniformity of sputtering film [2,3,4]. Ta ingots prepared by EBM have significant weaknesses including coarse grain size and extremely strong texture [6,7,8]. After subsequent processing, such as traditional rolling and annealing, texture bands, residual deformation bands and uneven grain size distribution are typical features in Ta plates [9,10,11]

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