LAUSR

Abstract Herein we report on the phases and microstructures obtained when Ni and commercial Ti2AlC powder mixtures - with Ti2AlC molar fractions of 0.1, 0.5 and 0.64 – are hot pressed (HPed) at 1050 °C for 2 h at a stress of 36 MPa in a vacuum hot press and then further annealed either at 1200 °C for 16 h or at 1350 °C for 16 h under the protection of high purity argon, Ar. After HPing, the 0.1 Ti2AlC composite sample was comprised of a Ni-based solid-solution with some dissolved Ti, fine TiCx particles and γ′ precipitates (Ni3(Al,Ti)). Heat treating at 1200 °C for 16 h did not change the phase content. However, after annealing at 1350 °C for 16 h, the TiCx phase substantially coarsened and become the major phase. HPing of the 0.5 Ti2AlC mixture, resulted in the formation of sub-stoichiometric TiCx, NiAl, Ti3NiAl2C, Ni2AlTi, and a small amount of Ti3AlC2. After annealing at 1200 °C for 16 h, the Ti3AlC2 phase disappeared. After the 1350 °C anneal, the Ni2AlTi phase was no longer detected and the microstructure was comprised of coarsened TiCx particles dispersed in a Ti-solutioned NiAl matrix with a small fraction of Ti3NiAl2C. Lastly, after HPing, the 0.64 Ti2AlC mixture, the phases present were TiCx, Ti3NiAl2C, NiAl, small amounts of Ti3AlC2 and traces of unreacted Ti2AlC. After annealing at 1200 or 1350 °C for 16 h, the Ti3AlC2 and Ti2AlC phases disappear, and a new ternary Al-rich aluminide, Ti6Al16Ni7 phase emerges. The final microstructure was thus comprised mostly of Ti6Al16Ni7 and TiCx. The reactions resulting in these compositions are developed.