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 1 50 K), grain size (63 to 165 mu m), and solid solution alloying additi ons of zirconium (Zr) on the fracture toughness (K-q, K-Ic) of polycry stalline niobium (Nb). Extensive fracture surface analyses of the frac tured specimens revealed the location of the apparent cleavage fractur e nucleation sites. Comparisons have been made to models for cleavage fracture toughness as well as to predictions of the peak stress locati ons using existing finite element models for a crack loaded under plan e strain conditions.