Effect of Mn content on the microstructure and mechanical properties of cast high Nb containing TiAl alloys

The microstructure and mechanical properties of two high Nb containing TiAI alloys with different Mn contents, Ti46Al8Nb2Mn0.2B and Ti46Al8Nb1.3Mn0.2B, were studied. XRD and SEM results show that the Ti46Al8Nb2Mn0.2B alloy obtains duplex microstrueture with a few brittle 13 phases after hot isostatic pressing (HIP) and cyclic heat treatment. By thermostatic treatment in two-phase area for long time after HIP, no β phases were found in the microstructure of the Ti46Al8Nb1.3Mn0.2B alloy. Tensile test shows that the mechanical properties improve with decreasing Mn content, and the elongation, yield strength and breaking strength of the Ti46Al8Nb1.3Mn0.2B alloy are 2.4%, 548 MPa and 660 MPa, respectively. The fracture morphologies indicate that the fracture of the two alloys at room temperature belongs to brittle cleavage fracture.