Reaction behavior and pore formation mechanism of TiAl–Nb porous alloys prepared by elemental powder metallurgy

• TiAl–Nb porous alloys are successfully fabricated by elemental powder metallurgy.
• Due to exothermal reaction, expansion of gas results in expansion of the compact.
• Volume expansion is restricted owing to vacancy migration and atomic diffusion.
• Phase transformation and atomic diffusion promote coalescence of pores.

Ti–48Al–6Nb (at.%) porous alloys are fabricated by elemental powder metallurgy to study the pore formation and propagation mechanism. Reactive diffusion, pore formation process, and pore characteristics of the porous TiAl–Nb alloys are investigated at different temperatures. It is found that the porous alloys exhibit a uniform, maze-like network skeleton, viz., a typical α2-TiAl3/γ-TiAl fully lamellar microstructure. The reactive diffusivities between Ti and Al powders are dominant during the Ti–Al–Nb powder sintering. Gas release during sintering also plays an important role in the pore propagation and the compact expanding process. In addition, a pore-formation model is proposed to interpret the growth mechanism of pores and skeletons.