Microstructural evolution, phase constitution and mechanical behaviour of Ni/TiCN reinforced TiAl matrix composites consolidated by spark plasma sintering

Fully densified TiAl composites reinforced with Ni and TiCN nanoparticles were successfully fabricated via the spark plasma sintering technique. The interrelationship between the phase constitution, microstructural evolution, and mechanical behaviour was systematically evaluated. SEM analyses of the sintered composites revealed a progressive refinement of the γ-TiAl and α₂-Ti₃Al grains in the matrix and the in-situ formation of Ti₂Ni and Ti₃AlC₂-strengthened networks at a 1 wt% TiCN content (TNi1TiCN). However, higher TiCN reinforcements resulted in particle clustering and heterogeneous microstructural regions, which impaired the mechanical performance of the materials. The hardness of the TNiTiCN composites increased steadily, with the TNi6TiCN composite exhibiting the highest hardness of about 434 ± 15.5 HV_1.0 compared to that of unreinforced TiAl alloy, sample T (311 ± 3.1 HV_1.0), due to dispersion strengthening, load transfer and MAX-phase contributions. In contrast, a peak compressive strength of 1960.95 ± 13.23 MPa and moderate ductility of 30.61 ± 0.77 % were observed in TNi1TiCN composite before declining due to reinforcement agglomeration at higher TiCN contents. Fractography revealed that fracture mechanisms evolved from cleavage-dominated behaviour in sample T to crack deflection and quasi-brittle fracture in the TNi and TNi1TiCN samples, and finally to agglomeration-driven brittle failure in the TNi6TiCN composite. Consequently, TNi1TiCN composite demonstrated the most favourable combination of strength, hardness and damage tolerance, highlighting the critical role of controlled reinforcement dispersion in achieving balanced mechanical performance in TiAl-based hybrid composites.