Hierarchically heterogeneous strategy for Ti2AlC/TiAl composite with superior mechanical properties

TiAl alloys have the merit of high specific strength, but usually suffer from poor room-temperature plasticity and inadequate high-temperature strength, limiting their practical applications in next-generation aerospace engines. Here we report a hierarchically heterogeneous strategy that endows Ti2AlC/TiAl composite with a sustained room-temperature strain-hardening capability and superior high-temperature strengthening effect. The exceptional mechanical properties are derived from hierarchically heterogeneous microstructure design with grain boundary distribution of continuous micro-Ti2AlC network and intragranular dispersion of high-density Ti2AlC nanoprecipitations. It is demonstrated that the micro-Ti2AlC network not only could delocalize plastic strains at ambient temperature via the activation of multiple dislocations, the formation of dislocations cells and the obstruction of crack, but also could enhance high-temperature strengthening effect via suppressing grain boundary softening in TiAl alloys. In addition, a novel finding is reported for the first time that the Ti2AlC nanoprecipitations could not only provide auxiliary slip systems in γ-TiAl matrix via inducing the formation of primary nanotwins (NTs) and the subsequent secondary NTs at ambient temperature, but also could tilt the propagation path of deformation twin, refine grain and twin width to accommodate high-temperature softening of composite. Our findings open up a new path for designing TiAl matrix composite with exceptional overall performance.