Phase transformation in Ti-48Al-6Nb porous alloys and its influence on pore properties

摘要

Ti-48Al-6Nb porous alloys were synthesized by the powder metallurgy (PM) method, and the associated phase transformation and pore parameter were investigated in order to reveal the pore-formation mechanism. The present results indicate that the Nb-Al and Ti-Al phase transformations contribute to the pore-formation. It was found that the five-step phase transformations for the Ti-48Al-6Nb porous alloys occur as follows: (1) Ti + Al → TiAl_3 at 600-700 ℃; (2) Nb + Al → NbAl_3 at 700-900 ℃; (3) TiAl_3 + Ti → TiAl at 900-1100 ℃; (4) TiAl + Ti → Ti_3Al/TiAl at 1100-1350 ℃; (5) NbAl_3 + Nb → Nb_2Al and the Ti_3Al turns to the major phase at 1350 ℃. These phase transformations made the pore-diameter increasing continuously from 1.71 μm to 12.10 μm and also made the pore volume distributing widely. At the second step of 700-900 ℃, the Nb-Al phase transformation leads to 5% more volume expansion compared to the Ti-Al based porous alloys. Meanwhile, the porosity and total pore area initially increase and then decrease at this step, but they increase intensely at the final step, which is needed as a catalytic carrier.