Environmental effects on the room temperature elongation in thermo-mechanically treated gamma+alpha(2) type titanium aluminides

TiAl(gamma), a promising high temperature intermetallic compound, suffers from its low ductility at room temperature, which is, reportedly, partly due to environmental brittlement. In this work, the environmental effect on room temperature elongation was investigated in polycrystalline Ti-48.5 mol%Al and Ti-49.9 mol%Al with four different microstructures (equi-axed, duplex, nearly lamellar and fully lamellar) controlled by thermo-mechanical treatment. The environmental effect was not recognized in tensile properties. In the equiaxed and duplex structure, the tensile elongation between 4 and 7.5% is nearly equal in vaccum and in air, indicating that the environmental effect is negligible. In the nearly lamellar and fully lamellar structures, the environmental effect cannot be detected because of very little tensile elongation around 1% in both environments. All the specimens after tensile test showed brittle fracture surfaces and no difference was found between the specimens tested in vacuum and in air.