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

Abstract

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 Ti 3 Al ( α 2 ) 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 α 2 lamellae, the spacing of α 2 lamellae, the volume fraction of the α 2 phase and γ domain size.