LEDGE MECHANISM OF PRIMARY ALPHA(2) GAMMA LAMELLAE GROWING IN THE SUPERSATURATED ALPHA(2) MATRIX FOR GAMMA-TIAL-BASED (GAMMA+ALPHA(2)) ALLOY/

gamma-TiAl-based (gamma+alpha(2)) two-phase alloys have been considere d as potential structural materials for relatively high temperature us e because of their good high-temperature properties. The service life of the alloy materials can be determined by the stability of the alpha (2)/gamma lamellar structure at high temperature [1 similar to 3]. The refore, a substantial research effort has been focused on alpha(2)/gam ma lamellae formation to understand the lamellar microstructure-proper ty relationships for alloys in this system [2, 4, 5]. The results show that the formation of primary lamellae is through either alpha-->L(al pha/gamma)-->L(alpha 2/gamma) or alpha-->alpha(2)(ss)-->L(alpha(2)/gam ma) transformation, where L and alpha(2)/gamma represent lamellae and supersaturated alpha(2) phase, respectively. The structures of both al pha and alpha(2) phases are hexagonal and alpha(2)(ss)(alpha(2)) is si mply an ordered version of the a phase [4 similar to 5]. The alpha(2)/ gamma lamellar structure is characterized by the orientation relations hips (0001)(alpha 2) //(111)(gamma), (1120)(alpha 2) //(110)(gamma) [4 , 6]. However, up to date there is very limited understanding on the n ature of primary alpha(2)/gamma lamellae formation. This paper aims at examining the precipitation micromechanism of gamma lamella in supers aturated alpha(2) matrix, including its nucleation and growth, by opti cal microscopy and transmission electron microscopy (TEM). The ledge m echanism of primary alpha(2)/gamma lamellae growth has been proposed, and the alpha(2)/gamma interfacial energy has been evaluated.