Isothermal transformation behavior of near-gamma TiAl alloys

Abstract

During the last few years near-gamma TiAl alloys have been considered as viable engineering materials for aerospace applications. A substantial amount of research effort has been directed towards the understanding of the microstructure-property relationship of these alloys. Similarly, fundamental studies have been conducted to understand the phase transformation mechanisms of single and two-phase titanium aluminides. The results of these studies have clearly established four types of microstructures: fully-lamellar, massive, equiaxed and duplex (lamellar + equiaxed). The two former types are developed through heating and cooling from the [alpha] phase region. Slow cooling produces the fully-lamellar structure and fast cooling leads to the massive microstructure. The two other types result from heating to and cooling from the ([alpha] + [gamma]) intercritical region. The development of the duplex or equiaxed structure depends on both the reheating temperature and holding time. The fully lamellar microstructure exhibits the best combination of mechanical properties at both room and high temperatures when compared to the other microstructures.