TWI Industrial Member Report Summary 633/1998
L S Smith and P L Threadgill
The titanium aluminide intermetallic compounds have many properties which are desirable for high-temperature structural materials, such as high specific strength and good creep resistance.
Background
In a previous review by one of the present authors, it was noted that these alloys had not progressed into structural applications, and that, before this could occur, the minimal knowledge available on joining methods must be increased substantially. At the time of this previous review, 1992, the Ti 3Al alloys were closer to industrial application than any of the other titanium aluminides. In the past few years, however, dramatic advances have been made in the understanding and alloy development of gamma-TiAl alloys and new orthorhombic alloys. Indeed, these have now surpassed the potential of Ti 3Al alloys.
Gamma-TiAl alloys are beginning to find application for aeroengine and automotive applications. Interest in other titanium aluminides, such as those based on the orthorhombic phase or TiAl 3, has grown recently. In this paper, the microstructure, properties and current status of the various titanium aluminides are reviewed and compared. Undoubtedly, the ?-TiAl alloys are currently the most important of the titanium aluminides and this review concentrates on these materials.
Welding technologies have advanced significantly over the past four years, for ?-TiAl, to the point where a critical review of the state-of-the-art may be beneficial in determining priorities for future research work. This present work has concentrated on metallurgical aspects of the joints, since a thorough understanding of these concepts is required before welding processes may be optimised.
Objective
To review critically the metallurgy and welding of titanium aluminide alloys, highlighting potential problems and areas where further work is necessary.