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

Highlights: • Porous skeletons with different phases can be synthesized at different temperatures. • The 5-step phase transformations are identified in the preparation of porous alloys. • Each phase transformation contributes to pore formation and volume changes. • Ti–48Al–6Nb porous alloys sintered at 1350 °C have the largest total pore area. - Abstract: 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 → TiAl₃ at 600–700 °C; (2) Nb + Al → NbAl₃ at 700–900 °C; (3) TiAl₃ + Ti → TiAl at 900–1100 °C; (4) TiAl + Ti → Ti₃Al/TiAl at 1100–1350 °C; (5) NbAl₃ + Nb → Nb₂Al and the Ti₃Al turns to the major phase at 1350 °C. 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 °C, 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.