Solid state infiltration of porous steel with aluminium by the forcefill process

We report first results on producing a metal - metal composite by forcing solid aluminium to fill a porous steel preform. This process is akin to forcefill used for filling of vias when producing metallic interconnects inmicroelectronics. Using scanning electron microscopy with energy-dispersive X-ray spectroscopy, it was shown that for nominal pore size as small as 100 um, the pores could be filled with aluminium throughout the entire preform used, thus demonstrating the viability of the process. An interesting aspect of this solid state 'infiltration' is that the tortuous random paths taken by the plastically flowing Al involve numerous kinks. Some of them may induce large localised shear deformation similar to that produced by equal channel angular pressing, which is used to fabricate bulk ultra-fine-grained materials. It is, therefore, conjectured that towards the exit end of the channels the infiltrating material may develop an ultra-fine grain structure and exhibit enhanced strength. It is suggested that the process described can be used to produce metal-metal (or ceramic-metal) composites with unusual mechanical properties. Thin fibres of the material that has percolated through the porous preform can be expected to have a sub-micron grain structure and to possess improved mechanical properties.