Effect of Ceramic Particle Additions on Foam Expansion and Stability in Compacted Al-TiH2 Powder Precursors



Al2O3, SiC and TiB2 particles have been added to Al-0.6 wt.% TiH2 powder mixtures. The resulting precursors were foamed and it was found that by adding as little as 3 vol. % of particles, the maximum foam expansion was increased from 350 % to 450 %. Microstructural investigations revealed that particles enhance foam expansion through a reduction in the critical cell wall thickness before rupture. The presence of oxide in the molten powder system tends to prevent good wetting, the ceramic phase is usually located at the cell walls, protruding into the cells and does not prevent drainage of liquid through the cell structure. An exception to this case was observed in the Al-SiC system where wetting is good and enhanced by reaction between the two phases. In this system the ceramic does not protrude into the cells and the rate of drainage is significantly reduced, giving improved foam stability.