Effects of Al-concentration and lamellar spacing on the room-temperature strength and ductility of PST crystals of TiAl

The tensile deformation behavior of PST crystals of TiAl with several different compositions (Ti–46–49.3 at.%Al) has been investigated in tension at room temperature as a function of crystal orientation (the angle φ between the lamellar boundaries and tensile axis) and crystal growth rate. The average thickness of TiAl (γ) lamellae as well as the average spacing of Ti3Al (α2) lamellae decreases with the decrease in Al-concentration and with the increase in growth rate. The yield stress for all orientations increases with decreasing Al concentration. While the value of tensile elongation for perpendicular (φ=90°) and intermediate (φ=31–68°) orientations does not significantly depend on Al concentration, the value for the parallel orientation (φ=0°) increases with decreasing Al concentration. The observed tensile behavior of these TiAl PST crystals are discussed in terms of microstructural features such as the thickness of both γ and α2 lamellae, the spacing of α2 lamellae, the volume fraction of the α2 phase and γ domain size.