Interface instability in the drawing process of copper/tantalum conductors

Copper/tantalum test billets have been cold drawn, using the process develo ped for the elaboration of copper/niobium multifilamentary conductors, for the development of high strength and high conductivity conductors for high pulsed magnetic fields. After a section reduction of 60%, a macroscopic rou ghness of the tantalum surface has been observed: two sets of perpendicular undulations developed (pa;allel and perpendicular to the drawing axis), wi th wavelengths in the 100 mu m range. This phenomenon, observed for the fir st time on bulk materials, is interpreted in terms of the Grinfeld instabil ity: the associated wavelength, calculated in the case of a shear stress di scontinuity at the interface between b.c.c. tantalum and f.c.c. copper, is found in the right magnitude range. (C) 1999 Acta Metallurgica Inc. Publish ed by Elsevier Science Ltd. All rights reserved.