Elevated temperature mechanical properties of Be 12Nb

Abstract

Bend strength, compression strength and fracture toughness of single-phase, vacuum hot pressed Be 12Nb have been assessed at temperatures from ambient to 1200°C. Hot hardness and indentation creep behavior was also determined for both vacuum hot pressed and hot isostatically pressed Be 12Nb over this same temperature range. Bend strength and fracture toughness increased with test temperature for the vacuum hot pressed Be 12Nb. Bend strength increased to a maximum of 220 MPa at 1000°C, while K IC increased from 2.5 MPa m 0.5 at 20°C to 4.5 MPa m 0.5 at 1100°C. Significant plastic deformation in bending was observed only above 1100°C. These results are consistent with a tensile ductile-to-brittle-transition (DBTT) of about 1100°C, with the bend strength at temperatures below 1100°C limited by the low fracture toughness. Tests in uniaxial compression revealed that yielding occured in the vacuum hot pressed material at temperatures above 700°C. High yield strengths (up to 1880 MPa) were measured at intermediate temperatures with a DBTT in compression between 700 and 800°C. Microhardness data indicated a DBTT of about 850°C for both the vacuum hot pressed and hot isostatically pressed Be 12Nb. Vickers microhardness values for the hot isostatically pressed material were significantly greater at low temperatures, but hot isostatic pressing and vacuum hot pressing heats are comparable at temperatures greater than 800°C. Indentation creep results indicated activation energies for dislocation creep of 290 and 220 kJ mol −1 with power law creep stress exponents of 4.3 and 6.6 for the hot isostically pressed and vacuum hot pressed beryllides respectively. This data is discussed using newly acquired information about dislocation slip in this alloy.