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

• Two types of aluminium solid solutions within the matrix of Al-MMCs. • Ti-enriched Al solid solution exhibits higher lattice parameter. • Additional strengthening mechanism Al-MMCs was discovered. • Linear increase of hardness and wear resistance with the TiC content. Structural heterogeneity is an inherent feature that occurs practically in all cast materials. In this work, we demonstrated that the chemical heterogeneity resulting from the SHS reaction of TiC formation in the aluminum A1000 alloy bath can enhance the strength by refining the matrix grains in in-situ cast TiC/A1000 composites. Using advanced characterization techniques including X-Ray synchrotron radiation diffraction, (S)TEM-HREM and SEM-EBSD studies, we identified two types of aluminum solid solutions within the dendritic grains of the A1000 matrix, distinguished by different lattice parameters. These differences result from the presence of unreacted titanium, which locally forms a supersaturated solid solution in the form of nanoprecipitates with a size of about 10 nm and a smaller lattice parameter compared to titanium-free regions. Another structural heterogeneity influencing the mechanical properties and fracture of composites is the agglomeration of TiC particles driven by the pushing and engulfment of particles at the crystallization front. Fractographic analysis revealed a correlation between mechanical properties and wear resistance in TiC/A1000 composites with TiC contents ranging from 5 to 15 vol%. In samples with more than 10 vol% TiC, particle agglomeration contributed to increased strength but reduced ductility, due to weakened interfacial bonding and non-uniform deformation under load.