Effects of heat treatment on dual phase structure carbides in Ti-34Al matrix composite

Ti-34Al matrix composite fabricated by melt-casting process was annealed at different temperatures. The constitution and morphology of carbides in composite were investigated using X-ray diffraction, scanning electron microscopy and electron probe microscope analysis. The results reveal that the as cast Ti-34Al composite is composed of Ti₃Al, TiAl, TiC and Ti ₃AlC in which carbides distributing at grain boundaries are TiC+Ti₃AlC dual phase structure. The core particle is TiC and the interfacial transition zone is Ti₃ AlC existing between TiC particle and α + γ matrix. Ti₃AlC is in equilibrium with α₂-Ti₃Al and γ-TiAl when the alloy was annealed at 900°C , while Ti₃AlC reaches equilibrium with α-Ti and γ-TiAl at 1 250°C. In α₂ + γ phase field, TiC+Ti₃AlC dual phase structure particles in as cast alloy change into thin elongated plate Ti₃AlC. When the composite was annealed in α + γ phase field, the dual phase structure particles change into single phase blocky and lath-like Ti₃AlC particles, and TiC in dual phase structure particles dissolved leading Ti to precipitate within Ti₃AlC particles. The volume fraction of Ti precipitates within the blocky particles is much higher than within lath-like particles.