Effects of Aluminum Content on Microstructure and Compressive Properties of TiAll Alloy

The effects of aluminum content on microstructure and compressive properties of TiAl alloy were investigated, and the failure mechanism was also discussed. It is interesting to find that the content of aluminum remarkably influences the microstructure of TiAl alloys fabricated by Induction Skull Melting technique. The microstructure of Ti-44.1Al (at%, similarly hereinafter) alloy is fully lamellar, and the gamma/alpha(2) lamellar colonies exhibit the characteristics of columnar crystals. The microstructure of Ti-47.3Al alloy is duplex, which contains gamma/alpha(2) lamellar colonies and gamma phase with 3D net structure. The microstructure of Ti-47.3Al alloy is much finer than that of Ti-44.1Al alloy. Compared with Ti-47.3Al alloy, Ti-44.1Al alloy exhibits higher yield strength, lower ultimate compressive strength, and lower ductility under both quasi-static compression and dynamic compression. Failure analysis after quasi-static compression shows that in Ti-44.1Al alloy, micro-pores initiation occurs in alpha(2) phase of gamma/alpha(2) lamellar colonies. In Ti-47.3Al alloy, micro-pores initiation starts in both alpha(2) phase of gamma/alpha(2) lamellar colonies and gamma phase with 3D net structure. Thus, the failure mechanisms of both Ti-44.1Al alloy and Ti-47.3Al alloy are micro-porous coalescence fracture under quasi-static compression. Failure analysis after dynamic compression shows that in Ti-44.1Al alloy, micro-cracks originate in phase boundary between gamma phase and alpha(2) phase. In Ti-47.3Al alloy, micro-cracks originate in both phase boundary of gamma/alpha(2) lamellar colonies and gamma phase with 3D net structure. With the increasing strain, the micro-cracks propagate rapidly, and cause the failure of the alloys under dynamic compression.