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 te nsion at room temperature as a function of crystal orientation (the an gle phi between the lamellar boundaries and tensile axis) and crystal growth rate. The average thickness of TiAl (gamma) lamellae as well as the average spacing of Ti3Al (alpha(2)) lamellae decreases with the d ecrease in Al-concentration and with the increase in growth rate. The yield stress for all orientations increases with decreasing Al concent ration. While the value of tensile elongation for perpendicular (phi = 90 degrees) and intermediate (phi = 31-68 degrees) orientations does not significantly depend on Al concentration, the value for the parall el orientation (phi = 0 degrees) increases with decreasing Al concentr ation. The observed tensile behavior of these TiAl PST crystals are di scussed in terms of microstructural features such as the thickness of both gamma and alpha(2) lamellae, the spacing of a, lamellae, the volu me fraction of the alpha(2) phase and gamma domain size. (C) 1997 Else vier Science S.A.