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 (+3 others)
2020 Materials Science & Engineering: A  
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 10 3 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
more » ... itive 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 .
doi:10.1016/j.msea.2020.140258 fatcat:sgqywngirjcvbdjhwtcwj7wbvu