Effects of test temperature, grain size, and alloy additions on the cleavage fracture stress of polycrystalline niobium

The current work investigates the effects of test temperature (77 to 131 K), grain size (63 to 165 mu m), and solid solution alloying additions of zirconium on the cleavage fracture stress (sigma(F)) of polycrystalline niobium. Extensive fracture surface analyses of fractured notched-bend specimens revealed the location of the apparent cleavage fracture nucleation sites, while comparisons have been made to peak stress locations using existing finite element models. The effects of such microstructural changes on the magnitude of the cleavage fracture stress are rationalized via comparisons to models for cleavage fracture.