Microstructural characterization and mechanical properties of TiAl–Al2Ti4C2–Al2O3–TiC in situ composites by hot-press-aided reaction synthesis

A new in situ multi-phase composite based on intermetallic TiAl is successfully reaction-synthesized from elemental powder mixtures of Ti, Al, TiO2 and C using hot-pressing-aided reaction synthesis technique (HPRS). The microstructure, flexural strength as well as fracture toughness of the monolithic TiAl-based compound and in situ composites are investigated. The products are mainly composed of Al2Ti4C2, TiC, Al2O3, Ti3Al and TiAl whereas Al3Ti is formed in case the starting powder mixtures contain more excess amount of Al. It is found that the formed fine Al2O3 and TiC particles tend to disperse on the grain boundaries. Although all of the three materials exhibit a typical brittle fracture mode, the fracture toughness of the in situ composites is substantially higher than that of the monolithic TiAl-based alloy by about 40–60% increase due to the toughening effect arising from interaction between the crack tip and the microstructures. However, the existence of residual porosity in the in situ composite samples in case of low external pressure applied to compacts during the reaction synthesis process results in insuperior flexural strength to that of the TiAl-based monolithic.