Fabrication of composite pipes by multi-billet extrusion technique

A processing technique named multi-billet extrusion (MBE) has been developed to fabricate clad composites. The MBE process is characterized by co-extruding several solid billets made of the same materials or of different ones, joining them in welding chambers and finally obtaining a desired extrudate by means of a die. It is capable of fabricating bimetallic, metal–ceramic, and ceramic–ceramic composite pipes. An extruded Al alloy/pure Al bimetallic pipe is bonded metallurgically due to the diffusion of Cu atoms across the interface during hot extrusion. In order to fabricate metal–ceramic composite pipes, a powder MBE method based on the plastic flow forming of pastes was used. It is shown that sound extrudates can be obtained no matter what mixing ratios of zirconia and stainless steel powders are used. It is possible to join inner and outer layers well after sintering, as long as the combinations of powder composition and binder content are adequate in the inner and outer layers. Moreover, the preparation of metal–ceramic three-layer pipes and ceramic–ceramic two-layer pipes by a similar powder MBE process is established as feasible.