Improvement of Microstructure and Mechanical Properties in TiB2-Doped TiAl Alloy by Direct Sheet Casting

Direct sheet casting of γTiAl with TiB 2 particle dispersion was made in order to improve the room temperature tensile ductility of the γTiAl sheets without decreasing their high-temperature strength. As a result, fine equiaxed grain microstructure was formed in the TiAl-1 at%TiB 2 sheet with the average grain size of 10 μm, the finest level among the current TiAl ingot specimens in the as-cast bulk condition. The room-temperature ductility was increased to 2.1% with the high-temperature tensile strength kept at the level of 200 MPa in the TiAl-1 at%TiB 2 sheet. This improvement of room-temperature ductility was attributable to the fact that the high oxygen content, i.e. 0.58 at%, of this material was not harmful to the tensile ductility when the oxygen existed in the solid solution of the α 2 fine lamellar phase or in finely distributed oxide particles, fine enough not to cause brittleness to the matrix. From these findings, it is determined that oxygen was not harmful to the ductility of γTiAl when its microstructure containing oxygen was fine enough.