HIGH TEMPERATURE MECHANICAL BEHAVIOUR OF CAST IN-SITU TiAl-BASED MATRIX COMPOSITE REINFORCED WITH Ti2AlC PARTICLES

Samples of in-situ TiAl-based matrix composite reinforced with Ti2AlC particles were prepared by vacuum induction melting of a charge with a nominal composition Ti-47Al-5Nb-1C-0.2B ( at%) in graphite crucibles and centrifugal casting into a graphite mould. The as-cast samples were subjected to hot isostatic pressing ( HIP) and multi-step heat treatments. High temperature compression tests at 1000 degrees C were carried out on the heattreated in-situ composite with an optimised microstructure. During compressive deformation, the work hardening is the predominant mechanism at small strains due to an increment of dislocation density in the insitu composite. At higher strains, dynamic recovery and recrystallization act as main softening mechanisms and exceed the work hardening, which leads to a decrease of the compressive flow stress with increasing strain. The creep deformation curves exhibit a primary creep stage, which is followed by a tertiary creep stage at temperatures ranging from 800 to 900 degrees C and applied stresses ranging from 150 to 250 MPa. The high temperature creep resistance of the studied in-situ composite is superior compared with that of some TiAlbased alloys with fully lamellar, nearly lamellar, convoluted and pseudo-duplex microstructures at a temperature of 800 degrees C and applied stress of 200 MPa.