The sintering densification, microstructure and mechanical properties of gamma Ti-48Al-2Cr-2Nb alloy with a small addition of copper

Titanium aluminide based alloys are difficult to consolidate by pressureless sintering. A systematic study has been made of the effect of small additions of copper on the sintering densification, microstructure and mechanical properties of gamma Ti-48Al-2Cr-2Nb (in at% throughout). The density of the Ti-48Al-2Cr-2Nb alloy sintered at 1375 °C for 120 min increased consistently from 74% theoretical density (TD) without Cu to >98%TD with an addition of up to 2 at%Cu. The enabling effect of a small addition of Cu is due to the formation of a wetting liquid, supported by dilatometry, differential scanning calorimetry (DSC) and Thermal-Calc analyses. Rapid sintering shrinkage occurred around 1251 °C and 1370 °C corresponding to liquid formation. Transmission electron microscopy (TEM) identified the formation of a Cu- and Cr-enriched hexagonal close-packed Ti(Al, Cr, Cu, Nb) phase with a=0.520 Å and c=0.803 Å. Its presence increased with increasing Cu content. The compressive, tensile and flexure properties of the as-sintered Ti-48Al-2Cr-2Nb-2Cu alloy were assessed. The tensile properties are similar or superior to those of the Ti-48Al-2Cr-2Nb alloy fabricated by metal injection moulding and sintering while the compression strength is about twice that of the as-cast Ti-48Al-2Cr-2Nb.