Effect of strain rate on tensile mechanical properties of high-purity niobium single crystals for SRF applications

J. F. Croteau, E. Pai Kulyadi, C. Kale, D. Siu, D. Kang, A. T. Perez Fontenla, E. García-Tabarés Valdivieso, T. R. Bieler, P. Eisenlohr, K. N. Solanki, D. Balint, P. A. Hooper, S. Atieh, N. Jacques, E. Cantergiani

Research output: Contribution to journalArticlepeer-review

1 Scopus citations

Abstract

An investigation of the mechanical properties of high-purity niobium single crystals is presented. Specimens were cut with different crystallographic orientations from a large grain niobium disk and uniaxial tensile tests were conducted at strain rates between 10-4 and 103 s-1. The logarithmic strain rate sensitivity for crystals oriented close to the center of a tensile axis inverse pole figure (IPF) is ~0.14 for all strain rates. The strain at failure (ranging from 0.4 to 0.9) is very sensitive to crystal orientation and maximal at ~10-2 s-1 for crystals oriented close to the center of an IPF. The high anisotropy observed at quasi-static strain rates decreased with increasing strain rate. The activation of multiple slip systems in the dynamic tests could account for this reduction in anisotropy. A transition from strain hardening to softening in the plastic domain was observed at strain rates greater than approximately 6 × 10-2 s-1 for crystals oriented close to the center of a tensile axis IPF. Shear bands were observed in specimens with orientations having similarly high Schmid factors on both {110}and {112}slip families, and they are correlated with reduced ductility. Crystal rotations at fracture are compared for the different orientations using scanning electron microscopy images and EBSD orientation maps. A rotation toward the terminal stable [101] orientation was measured for the majority of specimens (with tensile axes more than ~17° from the [001] direction) at strain rates between 1.28 × 10-2 and 1000 s-1.

Original languageEnglish (US)
Article number140258
JournalMaterials Science and Engineering A
Volume797
DOIs
StatePublished - Oct 21 2020

Keywords

  • Anisotropy
  • High strain rate
  • Niobium
  • SRF
  • Single crystal
  • Stress/strain measurements

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

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