Ti₂Al(C, N) Solid Solution Reinforcing TiAl-Based Composites: Evolution of a Core–Shell Structure, Interfaces, and Mechanical Properties

In this work, Ti2Al(C, N) solid solution with lamellar structure-enhanced TiAl matrix composites was synthesized by vacuum arc melting, using bulk g-C3N4, Ti, and Al powders as raw materials. The phases, microstructures, interfaces, and mechanical properties were investigated. MAX phase of Ti2Al(C, N) solid solution with lamellar structure was formed. During the melting process, first, C3N4 reacted with Ti to form Ti(C, N) by Ti + C3N4 → Ti(C, N). Then Ti2Al(C, N) was formed by a peritectic reaction of TiAl(l) + Ti(C, N)(s) → Ti2Al(C, N). C3N4 is the single reactant that provides C and N simultaneously to final product of Ti2Al(C, N). The interfaces of TiAl//Ti2Al(C, N) and Ti2Al(C, N)//Ti(C, N) display perfect orientation relationships with low misfit values. The microhardness, compressive strength, and strain of best-performing TiAl-10 mol % Ti2Al(C, N) composite were improved by 45%, 55.7%, and 50% compared with the TiAl alloy, respectively. Uniformly distributed Ti2Al(C, N) and unreacted Ti(C, N) particles contributed to the grain refinement and reinforcement of the TiAl matrix. Laminated tearing, particle pull-out, and the crack-arresting of Ti2Al(C, N) are crucial for the improvement in compressive strength and plasticity of the composites.