Tensile Properties, Superconductors

TEST APPARATUS AND TENSILE PROPERTIES OF NIOBIUM-ZIRCONIUM SUPERCONDUCTOR ALLOY WIRE IN THE TEMPERATURE RANGE 300° TO 4.2°K... 

Test Apparatus and Tensile Properties of Niobium-Zirconium Superconductor Alloy Wire 125... 

Test apparatus and techniques for testing fine wires in the temperature range of 4.2° to 300°K have been developed. These were successfully applied to an investigation of the tensile properties of Nb-Zr superconductor alloy wires. Cold-drawn wires of 0.005 and 0.010 in. diameter were found to have exceptionally high strength and to retain good ductility at temperatures as low as 4.2°K. The properties exhibited are well in excess of those currently required for superconductor solenoids. 

The influence of internal prestrains on the mechanical and Tc properties of NbaSn composite superconductors has been elucidated. Originating from differential thermal contraction in the composite wires, the prestrains amounted to a compressive load on the core and a tensile load on the bronze matrix. This effect saturated for matrix-to-core ratios exceeding 15 1, but provided for the application of tensile strains up to 1% before Tc degradation occurred. 

The Al-stabilized, 0.91-mm wire containing 121 NbTi filaments was tensile-tested in an Instron machine with a clip-on extensometer. The crosshead speeds were 8 nm/sec until the 0.2% yield strength and 40 nm/sec until wire fracture. The mechanical properties are compared in Table I with those of a Cu-stabilized superconductor tested in a similar manner. Although the yield stress and ultimate strength of the A1 conductor were lower than those of the Cu conductor, the A1 content may not have been causing the weakness. The lower proportion of NbTi in... 

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