Ultrafine-grained porous titanium and porous titanium/magnesium composites fabricated by space holder-enabled severe plastic deformation.

Compaction of powders by equal channel angular pressing (ECAP) using a novel space holder method was employed to fabricate metallic scaffolds with tuneable porosity. Porous Ti and Ti/Mg composites with 60% and 50% percolating porosity were fabricated using powder blends with two kinds of sacrificial space holders. The high compressive strength and good ductility of porous Ti and porous Ti/Mg obtained in this way are believed to be associated with the ultrafine grain structure of the pore walls. To understand this, a detailed electron microscopy investigation was employed to analyse the interface between Ti/Ti and Ti/Mg particles, the grain structures in Ti particles and the topography of pore surfaces. It was found that using the proposed compaction method, high quality bonding between particles was obtained. Comparing with other powder metallurgy methods to fabricate Ti with an open porous structure, where thermal energy supplied by a laser beam or high temperature sintering is essential, the ECAP process conducted at a relatively low temperature of 400°C was shown to produce unique properties.