Microstructure determined fracture behavior of a high Nb containing TiAl alloy

Static tensile and fatigue fracture behavior of a high Nb-containing TiAl alloy with the composition of Ti-45Al-8.5 Nb-(W, B, Y) fabricated by the plasma arc melting (PAM) have been investigated and correlated with microstructure in this work. The results show that the as-obtained alloy preserves near lamellar microstructure with homogeneous and relatively fine lamellar colonies. Meanwhile, minor β phase is observed on colony boundaries or within lamellar colonies. The existence of the random distributed borides is one of the main reasons for the refinement of the experimental alloy. The ultimate tensile strength of the experimental alloy is 710 MPa and the fatigue limit with the 50% survival rate is 309.6 MPa. The fracture mechanism has been proposed and correlated with the microstructure of the experimental TiAl alloy. It is found that fine lamellar microstructure accounts for the high fracture strength and moderate fatigue performance of the experimental high Nb-containing TiAl alloy. Fractography analysis indicates the alloy exhibits a predominant transgranular and occasional interlamellar fracture mode. The deformation incompatibilities occur at the boride/matrix and β phase/matrix interfaces lead to the crack initiation and propagation in these positions, which are detrimental to the ductility of the alloy.