Cu-Nb alloys prepared by mechanical alloying and subsequent heat treatment

Nanostructured Cu-Nb composites are prepared by mechanical alloying and a subsequent heat treatment. Up to 10 at.% Nb can be brought into solid solution by milling for 30 h at liquid nitrogen temperature. Subsequent to mechanical alloying a heat treatment was applied to precipitate the nobium from the solid solution in order to enhance both strength and conductivity of the material. The atmosphere present during the milling process strongly influences the phase formation. A high oxygen content within the powder leads to the formation of niobium oxide during the late state of milling and, later, prevents the formation of nobium precipitates by heat treatment. This occurs only in powder with a low oxygen content. A temperature of 400degreesC proves to be the optimum for strength, but too low to enhance the conductivity by complete precipitation of the Nb atoms. Almost all the nobium precipitates from the solid solution at 900 degreesC, but recrystallisation takes place at this temperature. Thus, the optimum heat treatment produces a balance between the mechanical and electrical properties and should be in the range of 600-700degreesC. (C) 2003 Elsevier B.V. All rights reserved.