Preliminary Observations on the Microstructure of Thin Wire Nb-44 per cent Ti Superconductor

Abstract

IT is well known that the critical current density (J_c) of a hard superconductor is controlled to some extent by the metallurgical structure of the material. Many commercially available superconducting materials contain filaments of Nb-Ti alloy of about 0.25 mm (0.01 in.) diameter, and a detailed examination of the structure of these fine filaments is therefore of considerable importance. Baker and Taylor¹ have pointed out the need for a three-dimensional study of the structure in order to correlate with critical current measurements. They also showed that test specimens should be in the same condition as for the superconductivity measurements and not undergo any further deformation prior to structural examination. Most of the ductile alloys with good superconducting properties have undergone a large degree of cold work, hence the structure is complex and there is a need for high resolution electron microscope examination of the specimen. Thin foils suitable for transmission electron microscopy have previously been prepared from longitudinal sections of fine wire but as Baker and Taylor¹ point out, it is necessary to examine the structure in the transverse plane in order to relate J_c to defect structure.