Comparative Study of Microstructure and Mechanical Properties of Two TiAl-Based Alloys Reinforced with Carbide...

Microstructure and mechanical properties of two TiAl-based alloys with nominal composition Ti-42.6Al-8.7Nb-0.3Ta-2.0C and Ti-41.0Al-8.7Nb-0.3Ta-3.6C (in at.%) were investigated and compared. The alloys were prepared by vacuum induction melting, followed by centrifugal casting. The as-cast samples were subjected to hot isostatic pressing and heat treatment consisting of solution annealing in β (Ti-based solid solution) phase field, cooling at a constant rate and stabilization annealing. The microstructure of the alloys consists of α₂ (Ti₃Al) + γ (TiAl) lamellar grains, single γ phase, coarse Ti₂AlC particles, and irregular shaped α₂ phase. The increase in the content of C at the expense of decreasing Al in the studied alloys affects solid-state phase transformation temperatures and leads to a decrease in size of grains and primary Ti₂AlC particles, increase in the volume fraction of reinforcing carbide particles, decrease in the volume fraction of lamellar colonies, and widening of the grain boundaries. Long-term ageing at 800 °C has no effect on the grain size but leads to the formation of Ti₄Al₃Nb particles and increase in interlamellar spacing. The Vickers hardness, microhardness of lamellar grains, indentation nanohardness, and elastic modulus of the boundary γ phase decrease during ageing. The Ti-42.6Al-8.7Nb-0.3Ta-2.0C alloy shows improved creep resistance compared to that of Ti-41.0Al-8.7Nb-0.3Ta-3.6C and some reference TiAl-based alloys at a temperature of 800 °C and applied stress of 200 MPa.