MELT-PROCESSED NI3AL MATRIX COMPOSITES REINFORCED WITH TIC PARTICLES

TiC-reinforced Ni3Al metal matrix composites have been investigated. The composites were prepared by in situ precipitation of either 0.01, 0.05, or 0.1 vol fraction TiC in molten Ni3Al. These precipitates are thermodynamically stable in the Ni3Al at 1000 degrees C up to 50 hours. Although almost ideal precipitate distribution was achieved at low volume fraction of TIC, at higher volume fraction, there was a tendency toward agglomeration.;Room and high-temperature mechanical testing showed significant improvement in modulus, yield strength, and ultimate,tensile strength, while still maintaining a 2.5 pet elongation at 0.1 vol. fraction TiC and 500 degrees C. The density of precipitates (number/m(3)) is strongly dependent on the fraction of TiC, on temperature, and on the holding time at that temperature. The critical nucleation temperature for these precipitates was determined to be at 1475 degrees C. Experimentally evaluated growth rate constants indicate a diffusion-controlled coarsening mechanism along with coalescence and multiparticle interaction at higher volume fractions of TiC. This is in accordance with either the Lifshitz Slyozov Encounter Modified (LSEM) model or with the Voorhees and Glicksman (VG) model.