État des recherches sur les matériaux composites à matrice intermetallique à base de Ti₃Al et de TiAl

Intermetallic matrix composite materials based on Ti₃Al and TiAl: a review

¹ IFI, Université de Marne-la-Vallée, Champs-sur-Marne, France
² Laboratoire des Multimatériaux et Interfaces, UMR CNRS 5615, Université Claude Bernard Lyon 1, Villeurbanne, France

Résumé

Abstract

This paper reviews developments on intermetallic matrix composites based on Ti₃Al and TiAl. By reinforcing intermetallic alloys with continuous long fibers such as SCS-6 and SM 1240, the objective is to leighten these materials and to improve the high temperature strength and stiffness beyond the monolithic levels. Compared to composites based on TiAl, composites using the Ti₃Al matrix have been more extensively investigated and the mechanical properties have been tested. Unidirectional composites exhibit outstanding longitudinal properties although properties transverse to the fiber direction are poor and generally lower than those of the corresponding monolithic matrices. This anisotropy results from the weak fibre/matrix interface. These composites are also submitted to environmental degradation. Concerning the TiAl/SCS-6 system, the plasma spraying process has been specifically developed to manufacture it. However, large tensile stresses, generated during cooling from the fabrication temperature or during thermal cycling, damage the matrix. In both composites, the major problem with continuous long SCS-6 fibres is the mismatch between the thermal expansion coefficient of the fibre and that of the matrix. If this mismatch can not be reduced due to the limited range of currently available fibres, an alternative approach might consist in using alumina fibres or in developing a new fibre. Efforts are in progress to solve some of the problems inherent to the choice of the fibre, matrix and interfacial characteristics. The successfull implementation of intermetallic matrix composites will provide substantial weight savings in aerospace systems.