In-situ Al2O3 ceramic-reinforced low-density iron-based composites via reactive casting: Microstructure evolution, reaction mechanism, and mechanical properties

Understanding reaction-driven ceramic formation in metallic melts is essential for designing ceramic-reinforced metal matrix composites with stable interfaces and reliable mechanical performance. In this study, in-situ Al 2 O 3 -reinforced iron-based metal matrix composites (IMMCs) were fabricated via reactive casting in an Fe-Al-CuO system. The effects of precursor composition and melting temperature on Al 2 O 3 formation, microstructure evolution, and mechanical properties were systematically investigated. The results show that melting temperature regulates a nucleation-growth competition mechanism governing Al 2 O 3 evolution. At 1550 °C, the reaction proceeds in a nucleation-dominated regime, producing fine and uniformly distributed Al 2 O 3 particles, whereas increasing the temperature to 1600 °C promotes particle coarsening and interconnection. Transmission electron microscopy analysis demonstrates the formation of a reaction-induced graded Al 2 O 3 /matrix interface with strong metallurgical bonding. The optimally processed composite ( IMMC 1550 °C 60 % ${\text{IMMC}}_{1550°C}^{60\%}$ ) exhibits an average Al 2 O 3 particle diameter of approximately 1.97 μm, with an area fraction of approximately 17.68%. It also achieves a Young's modulus of 203 GPa, an ultimate tensile strength of 672 MPa, and an elongation of 6.2%, corresponding to increases of 31% and 36% in stiffness and strength, respectively, compared with the unreinforced material. Thermodynamic calculations combined with ab initio molecular dynamics simulations confirm that the oxygen released from CuO preferentially bonds with Al in the Fe-Al-CuO melt, providing atomic-scale mechanistic evidence for in-situ Al 2 O 3 formation.