Processing and microstructure of functionally graded W/Cu composites fabricated by multi-billet extrusion using mechanically alloyed powders

A novel process – multi-billet extrusion was employed to produce a three-layer W/Cu functionally graded material, which is comprised of superfine W–15%Cu, W–25%Cu and W–35%Cu composite powders fabricated by mechanical alloying. An aqueous solution of water-soluble hydroxypropyl methylcellulose was used as binder. The effect of the content of binder on the quality of extrusion products is discussed. The extrusion behavior for W–Cu extrudates is analyzed. W/Cu green products were pressureless sintered at temperatures in the range of 1150–1300 °C for 1 h in hydrogen atmosphere. Three-layer W/Cu samples with a high density and a highly homogeneous microstructure were attained after sintering at 1250 °C for 1 h in hydrogen atmosphere. The mechanisms for enhancement of sinterability and improvement of density of the mechanically alloyed W–Cu powder products have been discussed. X-ray diffraction and scanning electron microscope respectively were used to identify and observe phase constitution and microstructure.