Defect Detection in Wire Manufacturing

Abstract

In the sequential drawing of metallic wires from an initial diameter of 196 mils (4.9 mm) to a final diameter just under 1 mil (25 μm), the wires sometimes break. Subsequent examination via TEM of broken Al wires [1] revealed that breaks occurred most often due to inclusions of Si almost as large as the wire diameter. The challenge is to devise a technique that can detect inclusions well before the wire is drawn to about the diameter of the inclusions. For example, if there is a larger diameter wire that has commercial use, and some inclusions are detected at that diameter, then the drawing-down process could be stopped at that point, and only the wires without inclusions will be drawn to smaller diameters. A different problem occurs in the manufacture of composite superconducting wires, most typically multifilament NbTi in a Cu matrix. Here the sausaging of NbTi filaments causes a reduced critical current. For this case the challenge is to devise a ]nondestructive method at room temperature for determining the integrity and quality of the NbTi filaments during or immediately after the fabrication process.