Three-dimensional printing of TiAl₃/Al₂O₃ composites

Intermetallic/ceramic composites were fabricated by reactive infiltration of an Al melt into a porous TiO₂ preform which was prepared by indirect three-dimensional printing. At 1450°C the highly negative Gibbs energy of reaction (ΔG_r = -279.950 kJ/mol) is the driving force for the redox reaction 13/2 Al + 3/2 TiO₂ → 3/2 TiAl ₃ + Al₂O₃ to take place. Wetting of molten Al on the preform surface was improved by adding a carbon-bearing binder ((C ₆H₁₀O₅)_n, dextrin) to the powder blend, which decomposed to amorphous carbon (carbon yield 25 wt.% of initial dextrin weight) after being heat-treated up to 800°C in an inert atmosphere. During annealing to 1400°C, carbon partially reduced TiO₂ at least on the surface of the grains to form Ti₃O₅ and Ti₂O₃, which exhibit a significantly lower wetting angle compared to TiO₂. In a low-oxygen-containing inert atmosphere and at 1200 °C, Al melt spontaneously penetrated into the printed preform via inter-agglomerate pores (mean size 8 μm) and intra-agglomerate pores (mean size 1 μm). A fine-grained TiAl₃/Al₂O₃ composite microstructure was produced with a residual porosity of 9 %.