Effect of microstructural heterogeneity on the strengthening and fracture mechanism in in-situ cast TiC/Al composites

Structural heterogeneity is an inherent feature that occurs practically in all cast materials. In this work, wedemonstrated that the chemical heterogeneity resulting from the SHS reaction of TiC formation in the aluminumAl1000 alloy bath can enhance the strength by refining the matrix grains in in-situ cast TiC/Al1000 composites.Using advanced characterization techniques including X-Ray synchrotron radiation diffraction, (S)TEM-HREMand SEM-EBSD studies, we identified two types of aluminum solid solutions within the dendritic grains of theAl1000 matrix, distinguished by different lattice parameters. These differences result from the presence ofunreacted titanium, which locally forms a supersaturated solid solution in the form of nanoprecipitates with asize of about 10 nm and a smaller lattice parameter compared to titanium-free regions. Another structuralheterogeneity influencing the mechanical properties and fracture of composites is the agglomeration of TiCparticles driven by the pushing and engulfment of particles at the crystallization front. Fractographic analysisrevealed a correlation between mechanical properties and wear resistance in TiC/Al1000 composites with TiCcontents ranging from 5 to 15 vol%. In samples with more than 10 vol% TiC, particle agglomeration contributedto increased strength but reduced ductility, due to weakened interfacial bonding and non-uniform deformationunder load.