The Metal Matrix composites (MMC) with aluminium matrix are today rather largely widespread in the mechanical engineering industry and in particular in the aeronautic field for parts subjected to loadings and moderate temperatures. Compared to traditional materials, these components MMC carried out by powder metallurgy present very attractive properties, because of addition of fine ceramic particles (generally SiCp < 5µm) : very high Young modulus, very good fatigue behaviour and fretting-fatigue, very good wear resistance. The stake is to extend their aeronautical application for more strongly loaded structure and/or exposed to high temperatures with a weight saving target (energy saving). In other words, the aim is to replace parts currently made of steel by these new materials. For that the solution consists in developing MMC with titanium matrix. The titanium alloys have the advantage of being much lighter than steels and especially much more resistant with respect to corrosion. On the other hand, they present weaker stiffness and thus induce larger deformations, potentially detrimental to designing. Various research is already running to solve this problem by introducing particles of reinforcements (carbides, borides) which increase the bulk properties (Young modulus) of theses materials while keeping a sufficient ductility. A second problem, quite as important, is that the titanium alloys, contrary to steels, present very bad tribological properties and in particular a very bad response with respect to fretting-cracking or fretting-fatigue. That results in a catastrophic reduction of the fretting-fatigue life time. Compared to a conventional fatigue, fretting loading induces a very fast activation of microscopic cracks on the surface resulting in a significant reduction of the life time and very severe drop of endurance going up to 1000%. The objective of COMETTi is to solve this problem by optimizing the composition of alloys and by carrying out suitable surface treatments in order to increase resistance to fretting-fatigue crack propagation. This optimization should preserve obviously the volumic properties what implies necessarily synergized research. Having solved these two hard points 'volumic properties' and 'fretting-fatigue', the MMC with titanium matrix thus optimized could be in particular considered for mechanical rotor and suspension of the large helicopters (8 with 12t), such as very highly loaded hugs and sleeves. The stake of the project Ti MMC COMETTi is thus to make it possible to reduce the causes and consequences of the fretting thanks to three targeted properties of this new materials : increased Young modulus, initiation cracks of the splits improved thanks to the hard particles contained in material which must improve the yield range, reduced crack propagation (stop effect of propagation related to the presence of the particles). The most promising way to obtain Ti MMC is powder metallurgy technology. Different reinforcements and matrix will be investigated and the relationship between elaboration conditions/microstructure/mechanical properties will be analysed. The main challenge will be to transfer material development at an industrial scale. The wear resistance of these materials will be reinforced by surface treatments development compatible with MMC (by reactive chemical plating starting from a gas phase or by PVD : OAS, nitride or HVOF coating). The fatigue-fretting behaviour will be characterized through fretting-fatigue, simple fretting, and fatigue tests on elementary specimen but also technological components. In order to rationalize the analysis of a contact in fretting-fatigue, one will introduce the concept of chart of Fretting-Fatigue. In addition an aspect modelling multi-scale of the CMM is envisaged in order to adapt the models of fretting-fatigue to a heterogeneous material. COMETTi will allow ? to support the emergence of MECACHROME as a French source of advanced materials what could create 5 fulltime employments - to propose an alternative solution to steels allowing a concept of more compact rotor, lighter of around 15 %, and increase inspection intervals (major reduction in the costs of maintenance). At the scientific level, COMETTi will make it possible to develop a national competence on the damage mechanisms and models associated of fatigue-fretting, in heterogeneous materials.