Effects of Ti₂AlC-TiB₂ on the microstructure and mechanical properties of TiAl matrix composites

Ti₂AlC-TiB₂ reinforced TiAl matrix composites were synthesized by vacuum arc melting using Ti, Al and B₄C powders as the raw materials. The effects of Ti₂AlC-TiB₂ contents on the phases, microstructures and mechanical properties of Ti₂AlC-TiB₂/TiAl composites were analyzed. The results show that Ti₂AlC-TiB₂/TiAl composites are mainly composed of TiAl, Ti₃Al, TiB₂ and Ti₂AlC phases, among which TiAl and Ti₃Al present a kind of lamellar structure and constitute the matrix. With the increasing of B₄C contents in the raw materials, the amount of synthesized Ti₂AlC and TiB₂ particles increases, and TiAl grains are refined greatly. In addition, TiB₂and Ti₂AlC particles distribute along the grain boundaries or in the grains.And Ti₂AlC particles are in lamellar or lath-like shapes with an average particle size of about 5-15 μm. The morphology of the TiB₂is related toits content. When the contents of Ti₂AlC-TiB₂ ceramic phase are less than 20wt%, TiB₂ particles are in a needle-rod shapes with a size of 0.5-5 μm. With the content increases to 30wt%, TiB₂ particles grow into blocky faceted particles from 5-20 μm. The Ti₂AlC is considered to be synthesized from a peritectic reaction between TiC and Ti-Al melt. The average hardness, ductility and the compressive strength of Ti₂AlC-TiB₂/TiAl composites increase obviously, with the formation and increase of Ti₂AlC-TiB₂. The mechanical properties of composites with 10wt% ceramic phases show the highest compression strength of 1591 MPa, and its fracture strain is 14% higher than that of pure TiAl alloy. The reinforcing mechanisms of the Ti₂AlC and TiB₂ include crack deflection, pinning and pull-out, which is benefit for the strengthening and ductility of Ti₂AlC-TiB₂/TiAl composites.