Effects of V and B, Y additions on the microstructure and creep behaviour of high-Nb TiAl alloys

The influence of the addition of V and B, Y on the microstructure, microsegregation and creep behaviour of the Ti-44Al-6Nb-1Cr (at.%) alloy is investigated. The creep tests performed at 800 °C and 150 MPa show that the Ti-44Al-6Nb-1Cr alloy with a small blocky microsegregation region and smooth colony boundary exhibits the poorest creep resistance. The addition of 2.0 V at.% promotes the formation of a γ phase in the microsegregation region and leads to a large blocky microsegregation area in the matrix. The large blocky microsegregation region with a low specific surface area provides colony boundary strengthening and improves creep resistance. The addition of B and Y affords an obvious refinement in the lamellar colony, provides an increasing opportunity for cavity nucleation at the colony boundary, and thus reduces the creep resistance. The creep failure mechanisms of the three alloys are compared and analysed.