Understanding metal–ceramic interfacial interactions in iron–carbide composites fabricated by laser-directed energy deposition

ABSTRACT Ensuring interface stability in metal matrix composites (MMCs) reinforced by ceramics is critical for achieving superior mechanical performance, particularly when processed via laser-directed energy deposition (LDED). In this study, iron (Fe)-based composites with 10 vol.% of titanium carbide (TiC), zirconium carbide (ZrC), and tungsten carbide (WC) were fabricated under identical volumetric energy density to understand interfacial effects. High-resolution microscopy revealed that all systems retained unmelted ceramic particles, though the extent of interfacial interaction varied significantly: TiC exhibited minimal dissolution with an interface width of ∼25 nm, ZrC showed partial dissolution and resolidified nanoscale precipitates (∼30 nm interface), while WC underwent substantial dissolution, forming a ∼4.5 μm thick Fe–W–C reaction zone. Nanoindentation mapping was employed to evaluate localized mechanical properties across the matrix, ceramic, and interfacial regions. The results revealed that the highest matrix hardness was for Fe–10TiC (6.3 GPa) and the lowest for Fe–10WC (4.6 GPa). The elastic modulus followed a different trend, with the highest value for Fe–10ZrC (213 GPa), then Fe–10TiC (201 GPa), and drastically lower for Fe–10WC (60.3 GPa). Interestingly, wear testing results contrasted with the hardness trend, with Fe–10WC showing the best wear resistance, likely due to strong interfacial bonding, ductile matrix accommodation, and spherical WC morphology. In contrast, Fe–10ZrC showed the highest wear rate, possibly due to particle pull-out and brittle fracture. The observed variation in interfacial and mechanical behavior is attributed to differences in thermodynamic stability, extent of particle dissolution, particle morphology, and the nature of bonding at the particle–matrix interface.