Effects of cold compacting pressure on the expansion behavior of Ti-48Al during sintering

Abstract

Porous TiAl intermetallic samples are successfully fabricated via an elemental powder metallurgy route. Cylindrical green samples are prepared by cold pressing of Ti-48Al elemental powders under different pressures. They are subsequently sintered in a dilatometer or a tube furnace. In the sintering, chemical reactions happens through discrepant diffusions between Ti and Al caused by the Kirkendall effect, which forms pores in the material and makes it expand in the sintering. The expansion happens in an anisotropic way, in which the axial expansion is larger than the radial expansion, especially for samples pressed under low pressure. As the compacting pressure increasing, the difference between axial and radial expansions gradually diminishes. Moreover, increasing pressure also leads to higher green density and better bonding between Ti and Al particles, therefore facilitating the diffusion and reactions between Ti and Al. As a result, the samples compacted under higher pressures experience larger expansion compared to those compacted under lower pressures. However, in spite of the larger expansion, the samples compacted under higher pressures still exhibit higher sintering density and compressive strength than those compacted under lower pressures.