Electronic International Standard Serial Number (EISSN)
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  orientation was measured for the majority of specimens (with tensile axes more than ~17° from the  direction) at strain rates between 1.28 × 10-2 and 1000 s-1.
Materials science and engineering
stress/strain measurements; niobium; single crystal; high strain rate; anisotropy; srf