DIFFUSION PATHS AND REACTION-MECHANISMS IN THE HIGH-TEMPERATURE CHEMICAL INTERACTION BETWEEN CARBON AND TITANIUM ALUMINIDES

After recalling the thermodynamic principles governing the high-temper ature chemical interactions in the Al-C-Ti system, an experimental stu dy has been undertaken in order to characterize the phases formed betw een graphite and titanium aluminides in powder mixtures heated at 1000 degrees C for increasing times and at the interface of semi-infinite diffusion couples hot-pressed at 1000-1150 degrees C under 100 MPa. Th e results are interpreted in terms of surface reaction and multiphase volume diffusion. More especially, relations between the reported phas e equilibria and the layer sequences observed at the interfaces of dif fusion couples are established and the key principles on the basis of which formation and growth of the reaction zones can be understood are pointed out.