RRR measurements and tensile tests of high purity large grain ingot niobium

Abstract

Residual resistivity ratio (RRR) measurements and tensile tests were performed on samples taken from seven high purity large grain niobium ingots produced by CBMM. Test specimens were taken from the top, middle and bottom regions of each ingot. The RRR measurements were performed with a GM cryocooler system and more than 60% of the samples exceeded RRR values of 250. Room temperature tensile tests were performed on samples from the same regions. 17 samples were machined according to ASTM standard test methods for tension testing of metallic material. Tests were performed with an Instron tensile/compression testing machine, and various mechanical properties such as Young’s modulus, 0.2% proof stress, ultimate tensile strength and strain at fracture were measured. For all the samples, the fracture strain exceeds 35% while the ultimate tensile stress is close to 100 MPa. Contents of impurity (N, O, C, H, Ta) of each region of the seven ingots were also measured. These data provide insights for a possible correlation among RRR values, mechanical properties and impurity contents of niobium ingots.