Effects of test temperature, grain size, and alloy additions on the low-temperature fracture toughness of polycrystalline niobium

The current work investigates the effects cf test temperature (77 to 150 K), grain size (63 to 165 mu m), and solid solution alloying additions of zirconium (Zr) on the fracture toughness (K-q, K-Ic) of polycrystalline niobium (Nb). Extensive fracture surface analyses of the fractured specimens revealed the location of the apparent cleavage fracture nucleation sites. Comparisons have been made to models for cleavage fracture toughness as well as to predictions of the peak stress locations using existing finite element models for a crack loaded under plane strain conditions.