Effects of refractory metals on microstructure and mechanical properties of directionally-solidified TiAl alloys

By using an appropriately oriented seed from the TiAl–Si system, the TiAl/Ti 3 Al lamellar structure was aligned parallel to the growth direction for ingots having composition of Ti–46Al–0.5Si–0.5X (X=Re, W and Mo) and Ti–47.5Al–0.5Re (at.%). The seeded and directionally solidified quaternary alloys containing either Re, W or Mo exhibit a nice balance of low- and high-temperature mechanical properties. Tensile elongation more than 20% is noted for the W- and Mo-containing alloys. The creep resistance for the three quaternary alloys is more than an order of magnitude better than other relevant TiAl alloys produced by conventional ingot metallurgy methods, with the best creep properties being obtained for the Re-containing alloy. The method to predict alloy compositions appropriate for aligning the lamellar structure of two-phase TiAl alloys of multi-component by directional solidification is proposed based on the assignment of ‘Al-equivalent’ for each of the alloying elements.