Plastic Deformation and Microstructure Evolution in Niobium at Temperatures from 1473 K to 1823 K

Plastic deformation and microstructure evolution are investigated at elevated temperatures in a low-impurity (ASTM B393-18 Type 1) niobium sheet material. Data from tensile tests are reported for temperatures from 1473 K to 1823 K (1200 °C to 1550 °C) at constant true-strain rates of 10−3 and 10−4 s−1. Microstructures produced by static annealing and by tensile deformation at these temperatures are characterized using backscatter electron imaging. Significant static grain growth is observed and increases with increasing temperature. Young’s elastic modulus data for niobium from the literature are reviewed to recommend modulus values from 293 K to 2300 K (20 °C to 2027 °C) for randomly textured polycrystalline niobium. Steady-state creep analysis of data above 1370 K (1097 °C), half the melting temperature, produces a stress exponent of 5.6 and an activation energy for creep of 454 kJ/mol, which is close to that of lattice self-diffusion. Dislocation substructure is observed following elevated temperature deformation. These data are compared with data from the literature to conclude that low-impurity niobium deforms by five-power creep across the conditions examined.