Improved weld strength of P/M bimetallic tubes and transition joints by means of nano interlayer particles

The joint strength between steel-Cu and Cu-Al tubes, produced by co-extrusion of sintered P/M preforms at room temperature, has been shown to increase by using nano-sized particles of nickel as an interlayer. The latter was applied in the form of powder to the contact area before cold extrusion and then heat treated under carefully controlled conditions. High strength joints were obtained as revealed by shear tests. The heat treatment temperatures were up to 150 °C lower than the temperature required for the interlayer powder of conventional size (several μm). The joints obtained had the additional advantage of preserving the quality of the dissimilar metal joints (steel-Cu and Cu-Al) in terms of similar physical, chemical and mechanical properties across the interface, i.e., very thin diffusion zone.