An Experimental and Computational Study of High-Temperature Creep Behavior in Fully Lamellar Titanium Aluminide Alloys

Titanium aluminide alloys have seen increased aerospace applications in recent years, especially in aircraft jet engines. They can offer benefits such as improved high-temperature strength compared to titanium alloys and reduced density compared to nickel alloys. These alloys also can exhibit high creep resistance due to their fully lamellar microstructure. These mechanical properties are desirable for components like turbine blades, where tight tolerances must be maintained for optimal performance. This research examines the high-temperature creep behavior of a fully lamellar two-phase titanium aluminide alloy, TNM® (Ti-43.5Al-4Nb-1Mo-0.1B), through experimental and computational methods. Scanning electron microscopy studies reveal the presence of large grains containing lamellar colonies in the pristine alloy. These colonies, examined by transmission electron microscopy, present alternating layers of γ-TiAl and α2-Ti3Al with average layer thicknesses of 100 nm and 80 nm respectively. TNM® specimens were tested under uniaxial tensile creep loading conditions at 800 ◦C with applied loads of 120 MPa, 150 MPa, and 300 MPa. The minimum creep strain rate increases nonlinearly with loading from 1.27×10−8 s−1 to 6.32×10−8 s−1 to 4.09×10−7 s−1 respectively. Synchrotron high-energy X-ray diffraction was performed on the tested specimens to characterize the lattice microstrain, dislocation density evolution, and phase stability. The dislocation density does not increase significantly with loading except where local plastic deformation occurs and is otherwise constant along the gauge length. The phase fraction was consistent across all three specimens, indicating phase stability at 800 ◦C up to 300 MPa. A dislocation-density-based crystal plasticity finite element model is developed to predict the creep behavior and understand the impact of loading and lamellar thickness on the creep strain rate. This work provides new insights into high-temperature deformation of fully lamellar titanium aluminides, enabling design and synthesis of new creep-resistant alloys.