Effect of carbon addition on creep behavior of cast TiAl alloy with hard-oriented directional lamellar microstructure

Two TiAl alloys, Ti-47.5Al-3.7(Cr, V, Zr) and Ti-47.5Al-3.7(Cr, V, Zr)-0.1C (at.%), were prepared by cold crucible levitation melting to couple the hard-oriented directional lamellar microstructure with carbon microalloying strengthening. The creep behavior and mechanism for the improvement in creep properties by carbon addition were investigated by mechanical tests and electron microscopy characterizations. The results show that obvious improvements on the creep properties at 760 degrees C and 276 MPa are achieved by 0.1 at.% C addition into TiAl alloy with directional lamellar microstructure, which promotes the creep strain and minimum creep rate decreasing with a large content. The minimum creep rate is reduced from 4.37 x 10(-8)to 3.97 x 10(-9) s(-1), and the duration entering into creep acceleration is prolonged for more than 10 times. The mechanism for creep property improvement by 0.1% C addition is attributed to two aspects. The first one is that Ti2AlC is found to be strong obstacles of 1/2[110] dislocations when moving across the lamellar interface in the carbon containing alloy. The other one is that the interfacial dislocations are effectively impeded and the release process is hindered by dynamic precipitation of Ti3AlC, which is proposed to be the special mechanism for creep resistance improvement of this hard-oriented directional lamellar microstructure.