Fabrication of sintered titanium alloy with heat-resistance

Sintering behavior and microstructures of Ti-(5∼10)mass%Al-(1-10)mass%Mo alloy compacts prepared by the technique of mixing Ti, TiAl and Mo powders were investigated by means of optical microscopy. Mechanical properties of the sintered materials were also examined in connection with microstructures. Addition of (5∼10)mass%Al and (1∼10)mass%Mo contributes to sintering densification of titanium compact, since the particle size of TiAl and Mo powders are much finer than that of Ti powder. While, the diffusion of Al and Mo atoms into titanium matrix greatly depend on temperature, so that the powder compacts have to be sintered for 3.6ks at a temperature above 1573K to obtain homogeneous materials in the chemical composition. The structure of compacts is of β(bec) single-phase at 1573K, but α (hep) phase precipitates during cooling from the sintering tempereature, When Al content is more than 8mass%, Ti₃Al can also precipitate and this makes the sintered materials brittle. On the other hand, when Mo content is more than 6mass%, α phase preferentially precipitates along grain boundary and this results in a decrease of elongation attributed to intergranular fracture. As a result of alloy design, Ti-8mass%Al-4mass%Mo alloy with fine two-phase structure of (α+β) was selected to obtain optimal tensile properties at both temperature of room temperature and 873K.